DotNETFrameworkNotesForProfessionals

DotNETFrameworkNotesForProfessionals

Notes for Professionals
.NET
.NET Framework
Framework
Notes for Professionals
100+ pages
of professional hints and tricks
GoalKicker.com Free Programming Books
Disclaimer This is an unocial free book created for educational purposes and is not aliated with ocial .NET Framework group(s) or company(s). All trademarks and registered trademarks are the property of their respective owners
Chapter 2: Strings
Chapter 3: DateTime parsing
Section 3.1: ParseExact Section 3.2: TryParse Section 3.3: TryParseExact Chapter 4: Dictionaries
Contents
About Chapter 1: Getting started with .NET Framework
Section 2.1: Count characters Section 2.2: Count distinct characters Section 2.3: Convert string to/from another encoding Section 2.4: Comparing strings Section 2.5: Count occurrences of a character Section 2.6: Split string into fixed length blocks Section 2.7: Object.ToString() virtual method Section 2.8: Immutability of strings
Section 1.1: Hello World in C# Section 1.2: Hello World in F# Section 1.3: Hello World in Visual Basic .NET Section 1.4: Hello World in C++/CLI Section 1.5: Hello World in IL Section 1.6: Hello World in PowerShell Section 1.7: Hello World in Nemerle Section 1.8: Hello World in Python (IronPython) Section 1.9: Hello World in Oxygene Section 1.10: Hello World in Boo
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Section 4.1: Initializing a Dictionary with a Collection Initializer Section 4.2: Adding to a Dictionary Section 4.3: Getting a value from a dictionary Section 4.4: Make a Dictionary with Case-Insensivitve keys Section 4.5: IEnumerable to Dictionary (≥ .NET 3.5) Section 4.6: Enumerating a Dictionary Section 4.7: ConcurrentDictionary (from .NET 4.0) Section 4.8: Dictionary to List Section 4.9: Removing from a Dictionary Section 4.10: ContainsKey(TKey) Section 4.11: ConcurrentDictionary augmented with Lazy’1 reduces duplicated computation
Section 6.1: Creating a ReadOnlyCollection Section 6.2: Updating a ReadOnlyCollection Section 6.3: Warning: Elements in a ReadOnlyCollection are not inherently read-only
Chapter 5: Collections
Section 5.1: Using collection initializers Section 5.2: Stack Section 5.3: Creating an initialized List with Custom Types Section 5.4: Queue
Chapter 6: ReadOnlyCollections
Chapter 7: Stack and Heap Section 7.1: Value types in use Section 7.2: Reference types in use
Chapter 8: LINQ
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Section 8.1: SelectMany (flat map) Section 8.2: Where (filter) Section 8.3: Any Section 8.4: GroupJoin Section 8.5: Except Section 8.6: Zip Section 8.7: Aggregate (fold) Section 8.8: ToLookup Section 8.9: Intersect Section 8.10: Concat Section 8.11: All Section 8.12: Sum Section 8.13: SequenceEqual Section 8.14: Min Section 8.15: Distinct Section 8.16: Count Section 8.17: Cast Section 8.18: Range Section 8.19: ThenBy Section 8.20: Repeat Section 8.21: Empty Section 8.22: Select (map) Section 8.23: OrderBy Section 8.24: OrderByDescending Section 8.25: Contains Section 8.26: First (find) Section 8.27: Single Section 8.28: Last Section 8.29: LastOrDefault Section 8.30: SingleOrDefault Section 8.31: FirstOrDefault Section 8.32: Skip Section 8.33: Take Section 8.34: Reverse Section 8.35: OfType Section 8.36: Max Section 8.37: Average Section 8.38: GroupBy Section 8.39: ToDictionary Section 8.40: Union Section 8.41: ToArray Section 8.42: ToList Section 8.43: ElementAt Section 8.44: ElementAtOrDefault Section 8.45: SkipWhile Section 8.46: TakeWhile
26 26 26 28 28 29 29 30 31 31 31 32 32 32 32 33 33 33 34 34 34 34 35 35 35 35 36 36 36 36 37 37 37 38 38 38 39 39 39 39 39 40 40 41 42 42 42 42 42 43
Section 8.47: DefaultIfEmpty Section 8.48: Join Section 8.49: Left Outer Join
Chapter 9: ForEach
Section 9.1: Extension method for IEnumerable Section 9.2: Calling a method on an object in a list
Chapter 10: Reflection
Chapter 12: Custom Types Section 12.1: Struct Definition Section 12.2: Class Definition Chapter 13: Code Contracts
Section 10.1: What is an Assembly? Section 10.2: Compare two objects with reflection Section 10.3: Creating Object and setting properties using reflection Section 10.4: How to create an object of T using Reflection Section 10.5: Getting an attribute of an enum with reflection (and caching it)
Chapter 11: Expression Trees
Section 11.1: building a predicate of form field == value Section 11.2: Simple Expression Tree Generated by the C# Compiler Section 11.3: Expression for retrieving a static field Section 11.4: InvocationExpression Class
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Section 13.1: Contracts for Interfaces Section 13.2: Installing and Enabling Code Contracts Section 13.3: Preconditions Section 13.4: Postconditions
Chapter 14: Settings
Section 14.1: AppSettings from ConfigurationSettings in .NET 1.x Section 14.2: Reading AppSettings from ConfigurationManager in .NET 2.0 and later Section 14.3: Introduction to strongly-typed application and user settings support from Visual Studio
Chapter 16: File Input/Output
Section 14.4: Reading strongly-typed settings from custom section of configuration file
Chapter 15: Regular Expressions (System.Text.RegularExpressions)
Section 15.1: Check if pattern matches input Section 15.2: Remove non alphanumeric characters from string Section 15.3: Passing Options Section 15.4: Match into groups Section 15.5: Find all matches Section 15.6: Simple match and replace
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Section 17.1: Reading a text file using StreamReader Section 17.2: Serial Ports using System.IO.SerialPorts Section 17.3: Reading/Writing Data Using System.IO.File
Section 16.1: C# File.Exists() Section 16.2: VB WriteAllText Section 16.3: VB StreamWriter Section 16.4: C# StreamWriter Section 16.5: C# WriteAllText()
Chapter 18: System.IO.File class
Chapter 17: System.IO
43 43 44 46 46 46 47 47 47 48 48 48 50 50 50 51 51 54 54 54 56 56 56 58 59 60 60 60
61 62 65 65 65 65 65 65 66 67 67 67 67 67 68 69 69 69 70 72
Chapter 19: Reading and writing Zip files
Section 19.1: Listing ZIP contents Section 19.2: Extracting files from ZIP files Section 19.3: Updating a ZIP file
Chapter 20: Managed Extensibility Framework
Section 20.1: Connecting (Basic) Section 20.2: Exporting a Type (Basic) Section 20.3: Importing (Basic)
Chapter 21: SpeechRecognitionEngine class to recognize speech
Chapter 24: .NET Core
Section 24.1: Basic Console App
Chapter 25: ADO.NET
Section 22.1: Adding Item to Cache (Set) Section 22.2: System.Runtime.Caching.MemoryCache (ObjectCache)
Chapter 23: System.Reflection.Emit namespace
Section 23.1: Creating an assembly dynamically
Section 21.1: Asynchronously recognizing speech based on a restricted set of phrases Section 21.2: Asynchronously recognizing speech for free text dictation
Chapter 22: System.Runtime.Caching.MemoryCache (ObjectCache)
Section 18.1: Delete a file Section 18.2: Strip unwanted lines from a text file Section 18.3: Convert text file encoding Section 18.4: Enumerate files older than a specified amount Section 18.5: Move a File from one location to another
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Section 28.1: Uninstalling a package from one project in a solution Section 28.2: Installing a specific version of a package Section 28.3: Adding a package source feed (MyGet, Klondike, ect) Section 28.4: Installing the NuGet Package Manager Section 28.5: Managing Packages through the UI Section 28.6: Managing Packages through the console Section 28.7: Updating a package Section 28.8: Uninstalling a package Section 28.9: Uninstall a specific version of package
Chapter 27: Platform Invoke Section 27.1: Marshaling structs Section 27.2: Marshaling unions Section 27.3: Calling a Win32 dll function Section 27.4: Using Windows API Section 27.5: Marshalling arrays
Section 25.1: Best Practices – Executing Sql Statements Section 25.2: Executing SQL statements as a command Section 25.3: Using common interfaces to abstract away vendor specific classes
Section 26.1: How Dependency Injection Makes Unit Testing Easier Section 26.2: Dependency Injection – Simple example Section 26.3: Why We Use Dependency Injection Containers (IoC Containers)
72 73 73 74 74 76 76 76 76 78 78 78 79 80 80 80 81 81 81 83 83 86 86 87 87 88 89 90 90 90 91 94 94 95 96 97 97 98 98 98 98 98 99 99 99 100 100
101
Chapter 26: Dependency Injection
Chapter 28: NuGet packaging system
Section 32.1: Deserialization using System.Web.Script.Serialization.JavaScriptSerializer Section 32.2: Serialization using Json.NET Section 32.3: Serialization-Deserialization using Newtonsoft.Json Section 32.4: Deserialization using Json.NET Section 32.5: Dynamic binding Section 32.6: Serialization using Json.NET with JsonSerializerSettings
Chapter 33: JSON in .NET with Newtonsoft.Json
Section 33.1: Deserialize an object from JSON text Section 33.2: Serialize object into JSON
Chapter 34: XmlSerializer
Section 34.1: Formatting: Custom DateTime format Section 34.2: Serialize object Section 34.3: Deserialize object Section 34.4: Behaviour: Map array name to property (XmlArray) Section 34.5: Behaviour: Map Element name to Property Section 34.6: Eciently building multiple serializers with derived types specified dynamically
Chapter 35: VB Forms
Section 35.1: Hello World in VB.NET Forms Section 35.2: For Beginners Section 35.3: Forms Timer Chapter 36: JIT compiler
Section 36.1: IL compilation sample
Chapter 37: CLR
Section 29.1: Basic configuration and setup
Chapter 30: System.Net.Mail
Section 30.1: MailMessage Section 30.2: Mail with Attachment
Chapter 31: Using Progress and IProgress
Section 31.1: Simple Progress reporting Section 31.2: Using IProgress
Chapter 32: JSON Serialization
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101 103 103 104 105 105 105 107 107 107 108 108 108 109 110 110 110 111 111 111 111 111 112 112 115 115 115 115 118 118 121 121 122 122 122 122 123 125 125 127 127 127 129 129 130 130 130 131
Section 37.1: An introduction to Common Language Runtime
Chapter 38: TPL Dataflow
Section 38.1: Asynchronous Producer Consumer With A Bounded BuerBlock Section 38.2: Posting to an ActionBlock and waiting for completion Section 38.3: Linking blocks to create a pipeline Section 38.4: Synchronous Producer/Consumer with BuerBlock
Chapter 39: Threading
Section 39.1: Accessing form controls from other threads Chapter 40: Process and Thread anity setting
Section 40.1: Get process anity mask Section 40.2: Set process anity mask
Chapter 41: Parallel processing using .Net framework
Section 41.1: Parallel Extensions
Chapter 42: Task Parallel Library (TPL)
Section 42.1: Basic producer-consumer loop (BlockingCollection) Section 42.2: Parallel.Invoke Section 42.3: Task: Returning a value
Section 42.4: Parallel.ForEach Section 42.5: Parallel.For Section 42.6: Task: basic instantiation and Wait Section 42.7: Task.WhenAll Section 42.8: Flowing execution context with AsyncLocal Section 42.9: Parallel.ForEach in VB.NET Section 42.10: Task: WaitAll and variable capturing Section 42.11: Task: WaitAny Section 42.12: Task: handling exceptions (using Wait) Section 42.13: Task: handling exceptions (without using Wait) Section 42.14: Task: cancelling using CancellationToken Section 42.15: Task.WhenAny
Chapter 43: Task Parallel Library (TPL) API Overviews
Section 43.1: Perform work in response to a button click and update the UI
Chapter 44: Synchronization Contexts
Section 44.1: Execute code on the UI thread after performing background work
Chapter 45: Memory management
Section 45.1: Use SafeHandle when wrapping unmanaged resources Section 45.2: Unmanaged Resources Chapter 46: Garbage Collection
Section 46.1: A basic example of (garbage) collection Section 46.2: Live objects and dead objects – the basics Section 46.3: Multiple dead objects Section 46.4: Weak References Section 46.5: Dispose() vs. finalizers Section 46.6: Proper disposal and finalization of objects
Chapter 47: Exceptions
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131 131 132 132 132 133 133 134 134 134 135 136 137 137 138 138 139 139 139 141 141 141 142 142 143 144 146 146 147 147 148 148 149 150 150 150 152 153 153 154 155 158 161 161 161 162 162 162 163
Section 47.1: Catching and rethrowing caught exceptions Section 47.2: Using a finally block Section 47.3: Exception Filters Section 47.4: Rethrowing an exception within a catch block Section 47.5: Throwing an exception from a dierent method while preserving its information Section 47.6: Catching an exception Chapter 48: System.Diagnostics
Section 48.1: Run shell commands Section 48.2: Send Command to CMD and Receive Output Section 48.3: Stopwatch
Chapter 49: Encryption / Cryptography
Section 49.1: Encryption and Decryption using Cryptography (AES) Section 49.2: RijndaelManaged Section 49.3: Encrypt and decrypt data using AES (in C#) Section 49.4: Create a Key from a Password / Random SALT (in C#)
Chapter 50: Work with SHA1 in C#
Section 50.1: #Generate SHA1 checksum of a file Section 50.2: #Generate hash of a text
Chapter 51: Unit testing
Section 51.1: Adding MSTest unit testing project to an existing solution Section 51.2: Creating a sample test method
Chapter 52: Write to and read from StdErr stream
Chapter 55: HTTP servers
Chapter 56: HTTP clients
Chapter 57: Serial Ports
Section 52.1: Write to standard error output using Console Section 52.2: Read from standard error of child process
Chapter 53: Upload file and POST data to webserver
Section 53.1: Upload file with WebRequest
Chapter 54: Networking
Section 55.1: Basic read-only HTTP file server (ASP.NET Core) Section 55.2: Basic read-only HTTP file server (HttpListener)
Section 54.1: Basic TCP chat (TcpListener, TcpClient, NetworkStream) Section 54.2: Basic SNTP client (UdpClient)
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Section 56.1: Reading GET response as string using System.Net.HttpClient Section 56.2: Basic HTTP downloader using System.Net.Http.HttpClient Section 56.3: Reading GET response as string using System.Net.HttpWebRequest Section 56.4: Reading GET response as string using System.Net.WebClient Section 56.5: Sending a POST request with a string payload using System.Net.HttpWebRequest Section 56.6: Sending a POST request with a string payload using System.Net.WebClient Section 56.7: Sending a POST request with a string payload using System.Net.HttpClient
Section 57.1: Basic operation Section 57.2: List available port names Section 57.3: Asynchronous read Section 57.4: Synchronous text echo service Section 57.5: Asynchronous message receiver
Appendix A: Acronym Glossary Section A.1: .Net Related Acronyms
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1
Chapter 1: Getting started with .NET Framework
.NET Version Release Date 2002-02-13 1.0 2003-04-24 1.1 2005-11-07 2.0 2006-11-06 3.0 3.5 2007-11-19 3.5 SP1 2008-08-11 4.0 2010-04-12 2012-08-15 4.5 2013-10-17 4.5.1 4.5.2 2014-05-05 2015-07-20 4.6 2015-11-17 4.6.1 4.6.2 2016-08-02 2017-04-05 4.7 4.7.1 2017-10-17 Compact Framework Version Release Date 2000-01-01 1.0 2005-10-01 2.0 2007-11-19 3.5 2009-01-01 3.7 2013-06-01 3.9 Micro Framework Version Release Date 4.2 4.3 4.4
2011-10-04 2012-12-04 2015-10-20
Section 1.1: Hello World in C#
using System;
class Program { // The Main() function is the first function to be executed in a program static void Main() { // Write the string “Hello World to the standard out Console.WriteLine(“Hello World”); } }
Console.WriteLine has several overloads. In this case, the string “Hello World” is the parameter, and it will output the “Hello World” to the standard out stream during execution. Other overloads may call the .ToString of the
GoalKicker.com – .NET Framework Notes for Professionals
2
argument before writing to the stream. See the .NET Framework Documentation for more information.
Live Demo in Action at .NET Fiddle
Introduction to C#
Section 1.2: Hello World in F#
open System
[] let main argv = printfn “Hello World” 0
Live Demo in Action at .NET Fiddle
Introduction to F#
Section 1.3: Hello World in Visual Basic .NET
Imports System
Module Program Public Sub Main() Console.WriteLine(“Hello World”) End Sub End Module
Live Demo in Action at .NET Fiddle
Introduction to Visual Basic .NET
Section 1.4: Hello World in C++/CLI
using namespace System;
int main(array^ args) { Console::WriteLine(“Hello World”); }
Section 1.5: Hello World in IL
.class public auto ansi beforefieldinit Program extends [mscorlib]System.Object { .method public hidebysig static void Main() cil managed { .maxstack 8 IL_0000: nop IL_0001: ldstr “Hello World” IL_0006: call void [mscorlib]System.Console::WriteLine(string) IL_000b: nop IL_000c: ret }
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.method public hidebysig specialname rtspecialname instance void .ctor() cil managed { .maxstack 8 IL_0000: ldarg.0 IL_0001: call instance void [mscorlib]System.Object::.ctor() IL_0006: ret }
}
Section 1.6: Hello World in PowerShell
Write-Host “Hello World”
Introduction to PowerShell
Section 1.7: Hello World in Nemerle
System.Console.WriteLine(“Hello World”);
Section 1.8: Hello World in Python (IronPython)
print “Hello World”
import clr from System import Console Console.WriteLine(“Hello World”)
Section 1.9: Hello World in Oxygene
namespace HelloWorld;
interface
type App = class public class method Main(args: array of String); end;
implementation
class method App.Main(args: array of String); begin Console.WriteLine(‘Hello World’); end;
end.
Section 1.10: Hello World in Boo
print “Hello World”
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Chapter 2: Strings Section 2.1: Count characters
If you need to count characters then, for the reasons explained in Remarks section, you can’t simply use Length property because it’s the length of the array of System.Char which are not characters but code-units (not Unicode code-points nor graphemes). Correct code is then:
int length = text.EnumerateCharacters().Count();
A small optimization may rewrite EnumerateCharacters() extension method specifically for this purpose:
public static class StringExtensions { public static int CountCharacters(this string text) { if (String.IsNullOrEmpty(text)) return 0;
int count = 0; var enumerator = StringInfo.GetTextElementEnumerator(text); while (enumerator.MoveNext()) ++count;
return count; } }
Section 2.2: Count distinct characters
If you need to count distinct characters then, for the reasons explained in Remarks section, you can’t simply use Length property because it’s the length of the array of System.Char which are not characters but code-units (not Unicode code-points nor graphemes). If, for example, you simply write text.Distinct().Count() you will get incorrect results, correct code:
int distinctCharactersCount = text.EnumerateCharacters().Count();
One step further is to count occurrences of each character, if performance aren’t an issue you may simply do it like this (in this example regardless of case):
var frequencies = text.EnumerateCharacters() .GroupBy(x => x, StringComparer.CurrentCultureIgnoreCase) .Select(x => new { Character = x.Key, Count = x.Count() };
Section 2.3: Convert string to/from another encoding
.NET strings contain System.Char (UTF-16 code-units). If you want to save (or manage) text with another encoding you have to work with an array of System.Byte.
Conversions are performed by classes derived from System.Text.Encoder and System.Text.Decoder which, together, can convert to/from another encoding (from a byte X encoded array byte[] to an UTF-16 encoded System.String and vice-versa).
Because the encoder/decoder usually works very close to each other they’re grouped together in a class derived
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from System.Text.Encoding, derived classes offer conversions to/from popular encodings (UTF-8, UTF-16 and so on).
Examples: Convert a string to UTF-8 byte[] data = Encoding.UTF8.GetBytes(“This is my text”);
Convert UTF-8 data to a string var text = Encoding.UTF8.GetString(data);
Change encoding of an existing text file
This code will read content of an UTF-8 encoded text file and save it back encoded as UTF-16. Note that this code is not optimal if file is big because it will read all its content into memory:
var content = File.ReadAllText(path, Encoding.UTF8); File.WriteAllText(content, Encoding.UTF16);
Section 2.4: Comparing strings
Despite String is a reference type == operator compares string values rather than references.
As you may know string is just an array of characters. But if you think that strings equality check and comparison is made character by character, you are mistaken. This operation is culture specific (see Remarks below): some character sequences can be treated as equal depending on the culture.
Think twice before short circuiting equality check by comparing Length properties of two strings!
Use overloads of String.Equals method which accept additional StringComparison enumeration value, if you need to change default behavior.
Section 2.5: Count occurrences of a character
Because of the reasons explained in Remarks section you can’t simply do this (unless you want to count occurrences of a specific code-unit):
int count = text.Count(x => x == ch);
You need a more complex function:
public static int CountOccurrencesOf(this string text, string character) { return text.EnumerateCharacters() .Count(x => String.Equals(x, character, StringComparer.CurrentCulture)); }
Note that string comparison (in contrast to character comparison which is culture invariant) must always be performed according to rules to a specific culture.
Section 2.6: Split string into fixed length blocks
We cannot break a string into arbitrary points (because a System.Char may not be valid alone because it’s a combining character or part of a surrogate) then code must take that into account (note that with length I mean the
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number of graphemes not the number of code-units):
public static IEnumerable Split(this string value, int desiredLength) { var characters = StringInfo.GetTextElementEnumerator(value); while (characters.MoveNext()) yield return String.Concat(Take(characters, desiredLength)); }
private static IEnumerable Take(TextElementEnumerator enumerator, int count) { for (int i = 0; i < count; ++i) { yield return (string)enumerator.Current;
if (!enumerator.MoveNext()) yield break; } }
Section 2.7: Object.ToString() virtual method
Everything in .NET is an object, hence every type has ToString() method defined in Object class which can be overridden. Default implementation of this method just returns the name of the type:
public class Foo { }
var foo = new Foo(); Console.WriteLine(foo); // outputs Foo
ToString() is implicitly called when concatinating value with a string:
public class Foo { public override string ToString() { return "I am Foo"; } }
var foo = new Foo(); Console.WriteLine("I am bar and "+foo);// outputs I am bar and I am Foo
The result of this method is also extensively used by debugging tools. If, for some reason, you do not want to override this method, but want to customize how debugger shows the value of your type, use DebuggerDisplay Attribute (MSDN):
// [DebuggerDisplay("Person = FN {FirstName}, LN {LastName}")] [DebuggerDisplay("Person = FN {"+nameof(Person.FirstName)+"}, LN {"+nameof(Person.LastName)+"}")] public class Person { public string FirstName { get; set; } public string LastName { get; set;} // … }
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Section 2.8: Immutability of strings
Strings are immutable. You just cannot change existing string. Any operation on the string crates a new instance of the string having new value. It means that if you need to replace a single character in a very long string, memory will be allocated for a new value.
string veryLongString = … // memory is allocated string newString = veryLongString.Remove(0,1); // removes first character of the string.
If you need to perform many operations with string value, use StringBuilder class which is designed for efficient strings manipulation:
var sb = new StringBuilder(someInitialString); foreach(var str in manyManyStrings) { sb.Append(str); } var finalString = sb.ToString();
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Chapter 3: DateTime parsing Section 3.1: ParseExact
var dateString = "2015-11-24";
var date = DateTime.ParseExact(dateString, "yyyy-MM-dd", null); Console.WriteLine(date);
11/24/2015 12:00:00 AM
Note that passing CultureInfo.CurrentCulture as the third parameter is identical to passing null. Or, you can pass a specific culture.
Format Strings
Input string can be in any format that matches the format string
var date = DateTime.ParseExact("24|201511", "dd|yyyyMM", null); Console.WriteLine(date);
11/24/2015 12:00:00 AM
Any characters that are not format specifiers are treated as literals
var date = DateTime.ParseExact("2015|11|24", "yyyy|MM|dd", null); Console.WriteLine(date);
11/24/2015 12:00:00 AM
Case matters for format specifiers
var date = DateTime.ParseExact("2015-01-24 11:11:30", "yyyy-mm-dd hh:MM:ss", null); Console.WriteLine(date);
11/24/2015 11:01:30 AM
Note that the month and minute values were parsed into the wrong destinations.
Single-character format strings must be one of the standard formats
var date = DateTime.ParseExact("11/24/2015", "d", new CultureInfo("en-US")); var date = DateTime.ParseExact("2015-11-24T10:15:45", "s", null); var date = DateTime.ParseExact("2015-11-24 10:15:45Z", "u", null);
Exceptions
ArgumentNullException
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var date = DateTime.ParseExact(null, "yyyy-MM-dd", null); var date = DateTime.ParseExact("2015-11-24", null, null);
FormatException
var date = DateTime.ParseExact("", "yyyy-MM-dd", null); var date = DateTime.ParseExact("2015-11-24", "", null); var date = DateTime.ParseExact("2015-0C-24", "yyyy-MM-dd", null); var date = DateTime.ParseExact("2015-11-24", "yyyy-QQ-dd", null);
// Single-character format strings must be one of the standard formats var date = DateTime.ParseExact("2015-11-24", "q", null);
// Format strings must match the input exactly* (see next section) var date = DateTime.ParseExact("2015-11-24", "d", null); // Expects 11/24/2015 or 24/11/2015 for most cultures
Handling multiple possible formats
var date = DateTime.ParseExact("2015-11-24T10:15:45", new [] { "s", "t", "u", "yyyy-MM-dd" }, // Will succeed as long as input matches one of these CultureInfo.CurrentCulture, DateTimeStyles.None);
Handling culture differences
var dateString = "10/11/2015"; var date = DateTime.ParseExact(dateString, "d", new CultureInfo("en-US")); Console.WriteLine("Day: {0}; Month: {1}", date.Day, date.Month);
Day: 11; Month: 10
date = DateTime.ParseExact(dateString, "d", new CultureInfo("en-GB")); Console.WriteLine("Day: {0}; Month: {1}", date.Day, date.Month);
Day: 10; Month: 11
Section 3.2: TryParse
This method accepts a string as input, attempts to parse it into a DateTime, and returns a Boolean result indicating success or failure. If the call succeeds, the variable passed as the out parameter is populated with the parsed result.
If the parse fails, the variable passed as the out parameter is set to the default value, DateTime.MinValue.
TryParse(string, out DateTime)
DateTime parsedValue;
if (DateTime.TryParse("monkey", out parsedValue)) { Console.WriteLine("Apparently, 'monkey' is a date/time value. Who knew?"); }
This method attempts to parse the input string based on the system regional settings and known formats such as
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ISO 8601 and other common formats.
DateTime.TryParse("11/24/2015 14:28:42", out parsedValue); // true DateTime.TryParse("2015-11-24 14:28:42", out parsedValue); // true DateTime.TryParse("2015-11-24T14:28:42", out parsedValue); // true DateTime.TryParse("Sat, 24 Nov 2015 14:28:42", out parsedValue); // true
Since this method does not accept culture info, it uses the system locale. This can lead to unexpected results.
// System set to en-US culture bool result = DateTime.TryParse("24/11/2015", out parsedValue); Console.WriteLine(result);
False
// System set to en-GB culture bool result = DateTime.TryParse("11/24/2015", out parsedValue); Console.WriteLine(result);
False
// System set to en-GB culture bool result = DateTime.TryParse("10/11/2015", out parsedValue); Console.WriteLine(result);
True
Note that if you are in the US, you might be surprised that the parsed result is November 10, not October 11.
TryParse(string, IFormatProvider, DateTimeStyles, out DateTime)
if (DateTime.TryParse(" monkey ", new CultureInfo("en-GB"), DateTimeStyles.AllowLeadingWhite | DateTimeStyles.AllowTrailingWhite, out parsedValue) { Console.WriteLine("Apparently, ' monkey ' is a date/time value. Who knew?"); }
Unlike its sibling method, this overload allows a specific culture and style(s) to be specified. Passing null for the IFormatProvider parameter uses the system culture.
Exceptions
Note that it is possible for this method to throw an exception under certain conditions. These relate to the parameters introduced for this overload: IFormatProvider and DateTimeStyles.
NotSupportedException: IFormatProvider specifies a neutral culture ArgumentException: DateTimeStyles is not a valid option, or contains incompatible flags such as AssumeLocal and AssumeUniversal.
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Section 3.3: TryParseExact
This method behaves as a combination of TryParse and ParseExact: It allows custom format(s) to be specified, and returns a Boolean result indicating success or failure rather than throwing an exception if the parse fails.
TryParseExact(string, string, IFormatProvider, DateTimeStyles, out DateTime)
This overload attempts to parse the input string against a specific format. The input string must match that format in order to be parsed.
DateTime.TryParseExact("11242015", "MMddyyyy", null, DateTimeStyles.None, out parsedValue); // true
TryParseExact(string, string[], IFormatProvider, DateTimeStyles, out DateTime)
This overload attempts to parse the input string against an array of formats. The input string must match at least one format in order to be parsed.
DateTime.TryParseExact("11242015", new [] { "yyyy-MM-dd", "MMddyyyy" }, null, DateTimeStyles.None, out parsedValue); // true
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Chapter 4: Dictionaries Section 4.1: Initializing a Dictionary with a Collection Initializer
// Translates to `dict.Add(1, "First")` etc. var dict = new Dictionary() { { 1, “First” }, { 2, “Second” }, { 3, “Third” } };
// Translates to `dict[1] = “First”` etc. // Works in C# 6.0. var dict = new Dictionary() { [1] = “First”, [2] = “Second”, [3] = “Third” };
Section 4.2: Adding to a Dictionary
Dictionary dict = new Dictionary(); dict.Add(1, “First”); dict.Add(2, “Second”);
// To safely add items (check to ensure item does not already exist – would throw) if(!dict.ContainsKey(3)) { dict.Add(3, “Third”); }
Alternatively they can be added/set via the an indexer. (An indexer internally looks like a property, having a get and set, but takes a parameter of any type which is specified between the brackets) :
Dictionary dict = new Dictionary(); dict[1] = “First”; dict[2] = “Second”; dict[3] = “Third”;
Unlike the Add method which throws an exception, if a key is already contained in the dictionary, the indexer just replaces the existing value.
For thread-safe dictionary use ConcurrentDictionary:
var dict = new ConcurrentDictionary(); dict.AddOrUpdate(1, “First”, (oldKey, oldValue) => “First”);
Section 4.3: Getting a value from a dictionary
Given this setup code:
var dict = new Dictionary() { { 1, “First” },
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{ 2, “Second” }, { 3, “Third” } };
You may want to read the value for the entry with key 1. If key doesn’t exist getting a value will throw KeyNotFoundException, so you may want to first check for that with ContainsKey:
if (dict.ContainsKey(1)) Console.WriteLine(dict[1]);
This has one disadvantage: you will search through your dictionary twice (once to check for existence and one to read the value). For a large dictionary this can impact performance. Fortunately both operations can be performed together:
string value; if (dict.TryGetValue(1, out value)) Console.WriteLine(value);
Section 4.4: Make a Dictionary with Case- Insensivitve keys
var MyDict = new Dictionary(StringComparison.InvariantCultureIgnoreCase)
Section 4.5: IEnumerable to Dictionary (≥ .NET 3.5)
Create a Dictionary from an IEnumerable:
using System; using System.Collections.Generic; using System.Linq;
public class Fruits { public int Id { get; set; } public string Name { get; set; } }
var fruits = new[] { new Fruits { Id = 8 , Name = “Apple” }, new Fruits { Id = 3 , Name = “Banana” }, new Fruits { Id = 7 , Name = “Mango” }, };
// Dictionary key value var dictionary = fruits.ToDictionary(x => x.Id, x => x.Name);
Section 4.6: Enumerating a Dictionary
You can enumerate through a Dictionary in one of 3 ways:
Using KeyValue pairs
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Dictionary dict = new Dictionary(); foreach(KeyValuePair kvp in dict) { Console.WriteLine(“Key : ” + kvp.Key.ToString() + “, Value : ” + kvp.Value); }
Using Keys
Dictionary dict = new Dictionary(); foreach(int key in dict.Keys) { Console.WriteLine(“Key : ” + key.ToString() + “, Value : ” + dict[key]); }
Using Values
Dictionary dict = new Dictionary(); foreach(string s in dict.Values) { Console.WriteLine(“Value : ” + s); }
Section 4.7: ConcurrentDictionary (from .NET 4.0)
Represents a thread-safe collection of key/value pairs that can be accessed by multiple threads concurrently.
Creating an instance
Creating an instance works pretty much the same way as with Dictionary, e.g.:
var dict = new ConcurrentDictionary();
Adding or Updating
You might be surprised, that there is no Add method, but instead there is AddOrUpdate with 2 overloads:
(1) AddOrUpdate(TKey key, TValue, Func addValue) – Adds a key/value pair if the key does not already exist, or updates a key/value pair by using the specified function if the key already exists.
(2) AddOrUpdate(TKey key, Func addValue, Func updateValueFactory) – Uses the specified functions to add a key/value pair to the if the key does not already exist, or to update a key/value pair if the key already exists.
Adding or updating a value, no matter what was the value if it was already present for given key (1):
string addedValue = dict.AddOrUpdate(1, “First”, (updateKey, valueOld) => “First”);
Adding or updating a value, but now altering the value in update, based on the previous value (1):
string addedValue2 = dict.AddOrUpdate(1, “First”, (updateKey, valueOld) => $”{valueOld} Updated”);
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Using the overload (2) we can also add new value using a factory:
string addedValue3 = dict.AddOrUpdate(1, (key) => key == 1 ? “First” : “Not First”, (updateKey, valueOld) => $”{valueOld} Updated”);
Getting value
Getting a value is the same as with the Dictionary:
string value = null; bool success = dict.TryGetValue(1, out value);
Getting or Adding a value
There are two mehod overloads, that will get or add a value in a thread-safe manner.
Get value with key 2, or add value “Second” if the key is not present:
string theValue = dict.GetOrAdd(2, “Second”);
Using a factory for adding a value, if value is not present:
string theValue2 = dict.GetOrAdd(2, (key) => key == 2 ? “Second” : “Not Second.” );
Section 4.8: Dictionary to List
Creating a list of KeyValuePair:
Dictionary dictionary = new Dictionary(); List<KeyValuePair> list = new List<KeyValuePair>(); list.AddRange(dictionary);
Creating a list of keys:
Dictionary dictionary = new Dictionary(); List list = new List(); list.AddRange(dictionary.Keys);
Creating a list of values:
Dictionary dictionary = new Dictionary(); List list = new List(); list.AddRange(dictionary.Values);
Section 4.9: Removing from a Dictionary
Given this setup code:
var dict = new Dictionary() { { 1, “First” }, { 2, “Second” }, { 3, “Third” } };
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Use the Remove method to remove a key and its associated value.
bool wasRemoved = dict.Remove(2);
Executing this code removes the key 2 and it’s value from the dictionary. Remove returns a boolean value indicating whether the specified key was found and removed from the dictionary. If the key does not exist in the dictionary, nothing is removed from the dictionary, and false is returned (no exception is thrown).
It’s incorrect to try and remove a key by setting the value for the key to null.
dict[2] = null; // WRONG WAY TO REMOVE!
This will not remove the key. It will just replace the previous value with a value of null.
To remove all keys and values from a dictionary, use the Clear method.
dict.Clear();
After executing Clear the dictionary’s Count will be 0, but the internal capacity remains unchanged.
Section 4.10: ContainsKey(TKey)
To check if a Dictionary has an specifique key, you can call the method ContainsKey(TKey) and provide the key of TKey type. The method returns a bool value when the key exists on the dictionary. For sample:
var dictionary = new Dictionary() { {“F1”, new Customer() { FirstName = “Felipe”, … } }, {“C2”, new Customer() { FirstName = “Carl”, … } }, {“J7”, new Customer() { FirstName = “John”, … } }, {“M5”, new Customer() { FirstName = “Mary”, … } }, };
And check if a C2 exists on the Dictionary:
if (dictionary.ContainsKey(“C2”)) { // exists }
The ContainsKey method is available on the generic version Dictionary.
Section 4.11: ConcurrentDictionary augmented with Lazy’1 reduces duplicated computation Problem
ConcurrentDictionary shines when it comes to instantly returning of existing keys from cache, mostly lock free, and contending on a granular level. But what if the object creation is really expensive, outweighing the cost of context switching, and some cache misses occur?
If the same key is requested from multiple threads, one of the objects resulting from colliding operations will be eventually added to the collection, and the others will be thrown away, wasting the CPU resource to create the object and memory resource to store the object temporarily. Other resources could be wasted as well. This is really bad.
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Solution
We can combine ConcurrentDictionary with Lazy. The idea is that ConcurrentDictionary GetOrAdd method can only return the value which was actually added to the collection. The loosing Lazy objects could be wasted in this case too, but that’s not much problem, as the Lazy object itself is relatively unexpensive. The Value property of the losing Lazy is never requested, because we are smart to only request the Value property of the one actually added to the collection – the one returned from the GetOrAdd method:
public static class ConcurrentDictionaryExtensions { public static TValue GetOrCreateLazy( this ConcurrentDictionary<TKey, Lazy> d, TKey key, Func factory) { return d.GetOrAdd( key, key1 => new Lazy(() => factory(key1), LazyThreadSafetyMode.ExecutionAndPublication)).Value; } }
Caching of XmlSerializer objects can be particularly expensive, and there is a lot of contention at the application startup too. And there is more to this: if those are custom serializers, there will be a memory leak too for the rest of the process lifecycle. The only benefit of the ConcurrentDictionary in this case is that for the rest of the process lifecycle there will be no locks, but application startup and memory usage would be inacceptable. This is a job for our ConcurrentDictionary, augmented with Lazy:
private ConcurrentDictionary<Type, Lazy> _serializers = new ConcurrentDictionary<Type, Lazy>();
public XmlSerializer GetSerialier(Type t) { return _serializers.GetOrCreateLazy(t, BuildSerializer); }
private XmlSerializer BuildSerializer(Type t) { throw new NotImplementedException(“and this is a homework”); }
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Chapter 5: Collections Section 5.1: Using collection initializers
Some collection types can be initialized at the declaration time. For example, the following statement creates and initializes the numbers with some integers:
List numbers = new List(){10, 9, 8, 7, 7, 6, 5, 10, 4, 3, 2, 1};
Internally, the C# compiler actually converts this initialization to a series of calls to the Add method. Consequently, you can use this syntax only for collections that actually support the Add method.
The Stack and Queue classes do not support it.
For complex collections such as the Dictionary class, that take key/value pairs, you can specify each key/value pair as an anonymous type in the initializer list.
Dictionary employee = new Dictionary() {{44, “John”}, {45, “Bob”}, {47, “James”}, {48, “Franklin”}};
The first item in each pair is the key, and the second is the value.
Section 5.2: Stack
There is a collection in .Net used to manage values in a Stack that uses the LIFO (last-in first-out) concept. The basics of stacks is the method Push(T item) which is used to add elements in the stack and Pop() which is used to get the last element added and remove it from the stack. The generic version can be used like the following code for a queue of strings.
First, add the namespace:
using System.Collections.Generic;
and use it:
Stack stack = new Stack(); stack.Push(“John”); stack.Push(“Paul”); stack.Push(“George”); stack.Push(“Ringo”);
string value; value = stack.Pop(); // return Ringo value = stack.Pop(); // return George value = stack.Pop(); // return Paul value = stack.Pop(); // return John
There is a non generic version of the type, which works with objects.
The namespace is:
using System.Collections;
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And a code sample of non generic stack:
Stack stack = new Stack(); stack.Push(“Hello World”); // string stack.Push(5); // int stack.Push(1d); // double stack.Push(true); // bool stack.Push(new Product()); // Product object
object value; value = stack.Pop(); // return Product (Product type) value = stack.Pop(); // return true (bool) value = stack.Pop(); // return 1d (double) value = stack.Pop(); // return 5 (int) value = stack.Pop(); // return Hello World (string)
There is also a method called Peek() which returns the last element added but without removing it from the Stack.
Stack stack = new Stack(); stack.Push(10); stack.Push(20);
var lastValueAdded = stack.Peek(); // 20
It is possible to iterate on the elements on the stack and it will respect the order of the stack (LIFO).
Stack stack = new Stack(); stack.Push(10); stack.Push(20); stack.Push(30); stack.Push(40); stack.Push(50);
foreach (int element in stack) { Console.WriteLine(element); }
The output (without removing):
50 40 30 20 10
Section 5.3: Creating an initialized List with Custom Types
public class Model { public string Name { get; set; } public bool? Selected { get; set; } }
Here we have a Class with no constructor with two properties: Name and a nullable boolean property Selected. If we wanted to initialize a List, there are a few different ways to execute this.
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var SelectedEmployees = new List { new Model() {Name = “Item1”, Selected = true}, new Model() {Name = “Item2”, Selected = false}, new Model() {Name = “Item3”, Selected = false}, new Model() {Name = “Item4”} };
Here, we are creating several new instances of our Model class, and initializing them with data. What if we added a constructor?
public class Model {
public Model(string name, bool? selected = false) { Name = name; selected = Selected; } public string Name { get; set; } public bool? Selected { get; set; } }
This allows us to initialize our List a little differently.
var SelectedEmployees = new List { new Model(“Mark”, true), new Model(“Alexis”), new Model(“”) };
What about a Class where one of the properties is a class itself?
public class Model { public string Name { get; set; } public bool? Selected { get; set; } }
public class ExtendedModel : Model { public ExtendedModel() { BaseModel = new Model(); }
public Model BaseModel { get; set; } public DateTime BirthDate { get; set; } }
Notice we reverted the constructor on the Model class to simplify the example a little bit.
var SelectedWithBirthDate = new List { new ExtendedModel() { BaseModel = new Model { Name = “Mark”, Selected = true}, BirthDate = new DateTime(2015, 11, 23)
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}, new ExtendedModel() { BaseModel = new Model { Name = “Random”}, BirthDate = new DateTime(2015, 11, 23) } };
Note that we can interchange our List with Collection, ExtendedModel[], object[], or even simply [].
Section 5.4: Queue
There is a collection in .Net used to manage values in a Queue that uses the FIFO (first-in first-out) concept. The basics of queues is the method Enqueue(T item) which is used to add elements in the queue and Dequeue() which is used to get the first element and remove it from the queue. The generic version can be used like the following code for a queue of strings.
First, add the namespace:
using System.Collections.Generic;
and use it:
Queue queue = new Queue(); queue.Enqueue(“John”); queue.Enqueue(“Paul”); queue.Enqueue(“George”); queue.Enqueue(“Ringo”);
string dequeueValue; dequeueValue = queue.Dequeue(); // return John dequeueValue = queue.Dequeue(); // return Paul dequeueValue = queue.Dequeue(); // return George dequeueValue = queue.Dequeue(); // return Ringo
There is a non generic version of the type, which works with objects.
The namespace is:
using System.Collections;
Adn a code sample fo non generic queue:
Queue queue = new Queue(); queue.Enqueue(“Hello World”); // string queue.Enqueue(5); // int queue.Enqueue(1d); // double queue.Enqueue(true); // bool queue.Enqueue(new Product()); // Product object
object dequeueValue; dequeueValue = queue.Dequeue(); // return Hello World (string) dequeueValue = queue.Dequeue(); // return 5 (int) dequeueValue = queue.Dequeue(); // return 1d (double) dequeueValue = queue.Dequeue(); // return true (bool) dequeueValue = queue.Dequeue(); // return Product (Product type)
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There is also a method called Peek() which returns the object at the beginning of the queue without removing it the elements.
Queue queue = new Queue(); queue.Enqueue(10); queue.Enqueue(20); queue.Enqueue(30); queue.Enqueue(40); queue.Enqueue(50);
foreach (int element in queue) { Console.WriteLine(i); }
The output (without removing):
10 20 30 40 50
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Chapter 6: ReadOnlyCollections Section 6.1: Creating a ReadOnlyCollection Using the Constructor
A ReadOnlyCollection is created by passing an existing IList object into the constructor:
var groceryList = new List { “Apple”, “Banana” }; var readOnlyGroceryList = new ReadOnlyCollection(groceryList);
Using LINQ
Additionaly, LINQ provides an AsReadOnly() extension method for IList objects:
var readOnlyVersion = groceryList.AsReadOnly();
Note
Typically, you want to maintain the source collection privately and allow public access to the ReadOnlyCollection. While you could create a ReadOnlyCollection from an in-line list, you would be unable to modify the collection after you created it.
var readOnlyGroceryList = new List {“Apple”, “Banana”}.AsReadOnly(); // Great, but you will not be able to update the grocery list because // you do not have a reference to the source list anymore!
If you find yourself doing this, you may want to consider using another data structure, such as an ImmutableCollection.
Section 6.2: Updating a ReadOnlyCollection
A ReadOnlyCollection cannot be edited directly. Instead, the source collection is updated and the ReadOnlyCollection will reflect these changes. This is the key feature of the ReadOnlyCollection.
var groceryList = new List { “Apple”, “Banana” };
var readOnlyGroceryList = new ReadOnlyCollection(groceryList);
var itemCount = readOnlyGroceryList.Count; // There are currently 2 items
//readOnlyGroceryList.Add(“Candy”); // Compiler Error – Items cannot be added to a ReadOnlyCollection object groceryList.Add(“Vitamins”); // ..but they can be added to the original collection
itemCount = readOnlyGroceryList.Count; // Now there are 3 items var lastItem = readOnlyGroceryList.Last(); // The last item on the read only list is now “Vitamins”
View Demo
Section 6.3: Warning: Elements in a ReadOnlyCollection are not inherently read-only
If the source collection is of a type that is not immutable, elements accessed through a ReadOnlyCollection can be
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modified.
public class Item { public string Name { get; set; } public decimal Price { get; set; } }
public static void FillOrder() { // An order is generated var order = new List { new Item { Name = “Apple”, Price = 0.50m }, new Item { Name = “Banana”, Price = 0.75m }, new Item { Name = “Vitamins”, Price = 5.50m } };
// The current sub total is $6.75 var subTotal = order.Sum(item => item.Price);
// Let the customer preview their order var customerPreview = new ReadOnlyCollection(order);
// The customer can’t add or remove items, but they can change // the price of an item, even though it is a ReadOnlyCollection customerPreview.Last().Price = 0.25m;
// The sub total is now only $1.50! subTotal = order.Sum(item => item.Price); }
View Demo
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Chapter 7: Stack and Heap Section 7.1: Value types in use Value types simply contain a value.
All value types are derived from the System.ValueType class, and this includes most of the built in types.
When creating a new value type, the an area of memory called the stack is used. The stack will grow accordingly, by the size the declared type. So for example, an int will always be allocated 32 bits of memory on the stack. When the value type is no longer in scope, the space on the stack will be deallocated.
The code below demonstrates a value type being assigned to a new variable. A struct is being used as a convenient way to create a custom value type (the System.ValueType class cannot be otherwise extended).
The important thing to understand is that when assigning a value type, the value itself copied to the new variable, meaning we have two distinct instances of the object, that cannot affect each other.
struct PersonAsValueType { public string Name; }
class Program { static void Main() { PersonAsValueType personA;
personA.Name = “Bob”;
var personB = personA;
personA.Name = “Linda”;
Console.WriteLine( // Outputs ‘False’ – because object.ReferenceEquals( // personA and personB are referencing personA, // different areas of memory personB));
Console.WriteLine(personA.Name); // Outputs ‘Linda’ Console.WriteLine(personB.Name); // Outputs ‘Bob’ } }
Section 7.2: Reference types in use Reference types are comprised of both a reference to a memory area, and a value stored within that area. This is analogous to pointers in C/C++.
All reference types are stored on what is known as the heap. The heap is simply a managed area of memory where objects are stored. When a new object is instantiated, a part of the heap will be allocated for use by that object, and a reference to that location of the heap will be returned. The heap is managed and maintained by the garbage collector, and does not allow for manual intervention.
In addition to the memory space required for the instance itself, additional space is required to store the reference
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itself, along with additional temporary information required by the .NET CLR.
The code below demonstrates a reference type being assigned to a new variable. In this instance, we are using a class, all classes are reference types (even if static).
When a reference type is assigned to another variable, it is the reference to the object that is copied over, not the value itself. This is an important distinction between value types and reference types.
The implications of this are that we now have two references to the same object. Any changes to the values within that object will be reflected by both variables.
class PersonAsReferenceType { public string Name; }
class Program { static void Main() { PersonAsReferenceType personA;
personA = new PersonAsReferenceType { Name = “Bob” };
var personB = personA;
personA.Name = “Linda”;
Console.WriteLine( // Outputs ‘True’ – because object.ReferenceEquals( // personA and personB are referencing personA, // the *same* memory location personB));
Console.WriteLine(personA.Name); // Outputs ‘Linda’ Console.WriteLine(personB.Name); // Outputs ‘Linda’ }
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Chapter 8: LINQ
LINQ (Language Integrated Query) is an expression that retrieves data from a data source. LINQ simplifies this situation by offering a consistent model for working with data across various kinds of data sources and formats. In a LINQ query, you are always working with objects. You use the same basic coding patterns to query and transform data in XML documents, SQL databases, ADO.NET Datasets, .NET collections, and any other format for which a provider is available. LINQ can be used in C# and VB.
Section 8.1: SelectMany (flat map)
Enumerable.Select returns an output element for every input element. Whereas Enumerable.SelectMany produces a variable number of output elements for each input element. This means that the output sequence may contain more or fewer elements than were in the input sequence.
Lambda expressions passed to Enumerable.Select must return a single item. Lambda expressions passed to Enumerable.SelectMany must produce a child sequence. This child sequence may contain a varying number of elements for each element in the input sequence.
Example
class Invoice { public int Id { get; set; } }
class Customer { public Invoice[] Invoices {get;set;} }
var customers = new[] { new Customer { Invoices = new[] { new Invoice {Id=1}, new Invoice {Id=2}, } }, new Customer { Invoices = new[] { new Invoice {Id=3}, new Invoice {Id=4}, } }, new Customer { Invoices = new[] { new Invoice {Id=5}, new Invoice {Id=6}, } } };
var allInvoicesFromAllCustomers = customers.SelectMany(c => c.Invoices);
Console.WriteLine( string.Join(“,”, allInvoicesFromAllCustomers.Select(i => i.Id).ToArray()));
Output:
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1,2,3,4,5,6
View Demo
Enumerable.SelectMany can also be achieved with a syntax-based query using two consecutive from clauses:
var allInvoicesFromAllCustomers = from customer in customers from invoice in customer.Invoices select invoice;
Section 8.2: Where (filter)
This method returns an IEnumerable with all the elements that meets the lambda expression
Example
var personNames = new[] { “Foo”, “Bar”, “Fizz”, “Buzz” };
var namesStartingWithF = personNames.Where(p => p.StartsWith(“F”)); Console.WriteLine(string.Join(“,”, namesStartingWithF));
Output:
Foo,Fizz
View Demo
Section 8.3: Any
Returns true if the collection has any elements that meets the condition in the lambda expression:
var numbers = new[] {1,2,3,4,5};
var isNotEmpty = numbers.Any(); Console.WriteLine(isNotEmpty); //True
var anyNumberIsOne = numbers.Any(n => n == 1); Console.WriteLine(anyNumberIsOne); //True
var anyNumberIsSix = numbers.Any(n => n == 6); Console.WriteLine(anyNumberIsSix); //False
var anyNumberIsOdd = numbers.Any(n => (n & 1) == 1); Console.WriteLine(anyNumberIsOdd); //True
var anyNumberIsNegative = numbers.Any(n => n dev.Id, innerKeySelector: proj => proj.DeveloperId, resultSelector: (dev, projs) => new { DeveloperName = dev.Name, ProjectNames = projs.Select(p => p.Name).ToArray()}); foreach(var item in grouped) { Console.WriteLine( “{0}’s projects: {1}”, item.DeveloperName, string.Join(“, “, item.ProjectNames)); }
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//Foobuzz’s projects: Hello World 3D, Super Fizzbuzz Maker //Barfizz’s projects: Citizen Kane – The action game, Pro Pong 2016
Section 8.5: Except
var numbers = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; var evenNumbersBetweenSixAndFourteen = new[] { 6, 8, 10, 12 };
var result = numbers.Except(evenNumbersBetweenSixAndFourteen);
Console.WriteLine(string.Join(“,”, result));
//1, 2, 3, 4, 5, 7, 9
Section 8.6: Zip
.NET Version ≥ 4.0 var tens = new[] {10,20,30,40,50}; var units = new[] {1,2,3,4,5};
var sums = tens.Zip(units, (first, second) => first + second);
Console.WriteLine(string.Join(“,”, sums));
//11,22,33,44,55
Section 8.7: Aggregate (fold)
Generating a new object in each step:
var elements = new[] {1,2,3,4,5};
var commaSeparatedElements = elements.Aggregate( seed: “”, func: (aggregate, element) => $”{aggregate}{element},”); Console.WriteLine(commaSeparatedElements); //1,2,3,4,5,
Using the same object in all steps:
var commaSeparatedElements2 = elements.Aggregate( seed: new StringBuilder(), func: (seed, element) => seed.Append($”{element},”)); Console.WriteLine(commaSeparatedElements2.ToString()); //1,2,3,4,5,
Using a result selector:
var commaSeparatedElements3 = elements.Aggregate( seed: new StringBuilder(), func: (seed, element) => seed.Append($”{element},”), resultSelector: (seed) => seed.ToString()); Console.WriteLine(commaSeparatedElements3); //1,2,3,4,5,
If a seed is omitted, the first element becomes the seed:
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var seedAndElements = elements.Select(n=>n.ToString()); var commaSeparatedElements4 = seedAndElements.Aggregate( func: (aggregate, element) => $”{aggregate}{element},”);
Console.WriteLine(commaSeparatedElements4); //12,3,4,5,
Section 8.8: ToLookup
var persons = new[] { new { Name=”Fizz”, Job=”Developer”}, new { Name=”Buzz”, Job=”Developer”}, new { Name=”Foo”, Job=”Astronaut”}, new { Name=”Bar”, Job=”Astronaut”}, };
var groupedByJob = persons.ToLookup(p => p.Job);
foreach(var theGroup in groupedByJob) { Console.WriteLine( “{0} are {1}s”, string.Join(“,”, theGroup.Select(g => g.Name).ToArray()), theGroup.Key); }
//Fizz,Buzz are Developers //Foo,Bar are Astronauts
Section 8.9: Intersect
var numbers1to10 = new[] {1,2,3,4,5,6,7,8,9,10}; var numbers5to15 = new[] {5,6,7,8,9,10,11,12,13,14,15};
var numbers5to10 = numbers1to10.Intersect(numbers5to15);
Console.WriteLine(string.Join(“,”, numbers5to10));
//5,6,7,8,9,10
Section 8.10: Concat
var numbers1to5 = new[] {1, 2, 3, 4, 5}; var numbers4to8 = new[] {4, 5, 6, 7, 8};
var numbers1to8 = numbers1to5.Concat(numbers4to8);
Console.WriteLine(string.Join(“,”, numbers1to8));
//1,2,3,4,5,4,5,6,7,8
Note that duplicates are kept in the result. If this is undesirable, use Union instead.
Section 8.11: All
var numbers = new[] {1,2,3,4,5};
var allNumbersAreOdd = numbers.All(n => (n & 1) == 1);
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Console.WriteLine(allNumbersAreOdd); //False
var allNumbersArePositive = numbers.All(n => n > 0); Console.WriteLine(allNumbersArePositive); //True
Note that the All method functions by checking for the first element to evaluate as false according to the predicate. Therefore, the method will return true for any predicate in the case that the set is empty:
var numbers = new int[0]; var allNumbersArePositive = numbers.All(n => n > 0); Console.WriteLine(allNumbersArePositive); //True
Section 8.12: Sum
var numbers = new[] {1,2,3,4};
var sumOfAllNumbers = numbers.Sum(); Console.WriteLine(sumOfAllNumbers); //10
var cities = new[] { new {Population = 1000}, new {Population = 2500}, new {Population = 4000} };
var totalPopulation = cities.Sum(c => c.Population); Console.WriteLine(totalPopulation); //7500
Section 8.13: SequenceEqual
var numbers = new[] {1,2,3,4,5}; var sameNumbers = new[] {1,2,3,4,5}; var sameNumbersInDifferentOrder = new[] {5,1,4,2,3};
var equalIfSameOrder = numbers.SequenceEqual(sameNumbers); Console.WriteLine(equalIfSameOrder); //True
var equalIfDifferentOrder = numbers.SequenceEqual(sameNumbersInDifferentOrder); Console.WriteLine(equalIfDifferentOrder); //False
Section 8.14: Min
var numbers = new[] {1,2,3,4};
var minNumber = numbers.Min(); Console.WriteLine(minNumber); //1
var cities = new[] { new {Population = 1000}, new {Population = 2500}, new {Population = 4000} };
var minPopulation = cities.Min(c => c.Population); Console.WriteLine(minPopulation); //1000
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Section 8.15: Distinct
var numbers = new[] {1, 1, 2, 2, 3, 3, 4, 4, 5, 5}; var distinctNumbers = numbers.Distinct();
Console.WriteLine(string.Join(“,”, distinctNumbers));
//1,2,3,4,5
Section 8.16: Count
IEnumerable numbers = new[] {1,2,3,4,5,6,7,8,9,10};
var numbersCount = numbers.Count(); Console.WriteLine(numbersCount); //10
var evenNumbersCount = numbers.Count(n => (n & 1) == 0); Console.WriteLine(evenNumbersCount); //5
Section 8.17: Cast
Cast is different from the other methods of Enumerable in that it is an extension method for IEnumerable, not for IEnumerable. Thus it can be used to convert instances of the former into instances of the later.
This does not compile since ArrayList does not implement IEnumerable:
var numbers = new ArrayList() {1,2,3,4,5}; Console.WriteLine(numbers.First());
This works as expected:
var numbers = new ArrayList() {1,2,3,4,5}; Console.WriteLine(numbers.Cast().First()); //1
Cast does not perform conversion casts. The following compiles but throws InvalidCastException at runtime:
var numbers = new int[] {1,2,3,4,5}; decimal[] numbersAsDecimal = numbers.Cast().ToArray();
The proper way to perform a converting cast to a collection is as follows:
var numbers= new int[] {1,2,3,4,5}; decimal[] numbersAsDecimal = numbers.Select(n => (decimal)n).ToArray();
Section 8.18: Range
The two parameters to Range are the first number and the count of elements to produce (not the last number).
// prints 1,2,3,4,5,6,7,8,9,10 Console.WriteLine(string.Join(“,”, Enumerable.Range(1, 10)));
// prints 10,11,12,13,14 Console.WriteLine(string.Join(“,”, Enumerable.Range(10, 5)));
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Section 8.19: ThenBy
ThenBy can only be used after a OrderBy clause allowing to order using multiple criteria
var persons = new[] { new {Id = 1, Name = “Foo”, Order = 1}, new {Id = 1, Name = “FooTwo”, Order = 2}, new {Id = 2, Name = “Bar”, Order = 2}, new {Id = 2, Name = “BarTwo”, Order = 1}, new {Id = 3, Name = “Fizz”, Order = 2}, new {Id = 3, Name = “FizzTwo”, Order = 1}, };
var personsSortedByName = persons.OrderBy(p => p.Id).ThenBy(p => p.Order);
Console.WriteLine(string.Join(“,”, personsSortedByName.Select(p => p.Name))); //This will display : //Foo,FooTwo,BarTwo,Bar,FizzTwo,Fizz
Section 8.20: Repeat
Enumerable.Repeat generates a sequence of a repeated value. In this example it generates “Hello” 4 times.
var repeats = Enumerable.Repeat(“Hello”, 4); foreach (var item in repeats) { Console.WriteLine(item); }
/* output: Hello Hello Hello Hello */
Section 8.21: Empty
To create an empty IEnumerable of int:
IEnumerable emptyList = Enumerable.Empty();
This empty IEnumerable is cached for each Type T, so that:
Enumerable.Empty() == Enumerable.Empty(); // This is True Enumerable.Empty() == Enumerable.Empty(); // This is False
Section 8.22: Select (map)
var persons = new[] { new {Id = 1, Name = “Foo”}, new {Id = 2, Name = “Bar”}, new {Id = 3, Name = “Fizz”}, new {Id = 4, Name = “Buzz”}
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};
var names = persons.Select(p => p.Name); Console.WriteLine(string.Join(“,”, names.ToArray()));
//Foo,Bar,Fizz,Buzz
This type of function is usually called map in functional programming languages.
Section 8.23: OrderBy
var persons = new[] { new {Id = 1, Name = “Foo”}, new {Id = 2, Name = “Bar”}, new {Id = 3, Name = “Fizz”}, new {Id = 4, Name = “Buzz”} };
var personsSortedByName = persons.OrderBy(p => p.Name);
Console.WriteLine(string.Join(“,”, personsSortedByName.Select(p => p.Id).ToArray()));
//2,4,3,1
Section 8.24: OrderByDescending
var persons = new[] { new {Id = 1, Name = “Foo”}, new {Id = 2, Name = “Bar”}, new {Id = 3, Name = “Fizz”}, new {Id = 4, Name = “Buzz”} };
var personsSortedByNameDescending = persons.OrderByDescending(p => p.Name);
Console.WriteLine(string.Join(“,”, personsSortedByNameDescending.Select(p => p.Id).ToArray()));
//1,3,4,2
Section 8.25: Contains
var numbers = new[] {1,2,3,4,5}; Console.WriteLine(numbers.Contains(3)); //True Console.WriteLine(numbers.Contains(34)); //False
Section 8.26: First (find)
var numbers = new[] {1,2,3,4,5};
var firstNumber = numbers.First(); Console.WriteLine(firstNumber); //1
var firstEvenNumber = numbers.First(n => (n & 1) == 0); Console.WriteLine(firstEvenNumber); //2
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The following throws InvalidOperationException with message “Sequence contains no matching element”:
var firstNegativeNumber = numbers.First(n => n n n (n & 1) == 0); Console.WriteLine(lastEvenNumber); //4
The following throws InvalidOperationException:
var lastNegativeNumber = numbers.Last(n => n (n & 1) == 0); Console.WriteLine(lastEvenNumber); //4
var lastNegativeNumber = numbers.LastOrDefault(n => n w.Length > 4); Console.WriteLine(lastLongWord); // three
var lastMissingWord = words.LastOrDefault(w => w.Length > 5);
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Console.WriteLine(lastMissingWord); // null
Section 8.30: SingleOrDefault
var oneNumber = new[] {5}; var theOnlyNumber = oneNumber.SingleOrDefault(); Console.WriteLine(theOnlyNumber); //5
var numbers = new[] {1,2,3,4,5};
var theOnlyNumberSmallerThanTwo = numbers.SingleOrDefault(n => n n (n & 1) == 0); Console.WriteLine(firstEvenNumber); //2
var firstNegativeNumber = numbers.FirstOrDefault(n => n w.Length > 3); Console.WriteLine(firstLongWord); // three
var firstMissingWord = words.FirstOrDefault(w => w.Length > 5); Console.WriteLine(firstMissingWord); // null
Section 8.32: Skip
Skip will enumerate the first N items without returning them. Once item number N+1 is reached, Skip starts returning every enumerated item:
var numbers = new[] {1,2,3,4,5};
var allNumbersExceptFirstTwo = numbers.Skip(2); Console.WriteLine(string.Join(“,”, allNumbersExceptFirstTwo.ToArray()));
//3,4,5
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Section 8.33: Take
This method takes the first n elements from an enumerable.
var numbers = new[] {1,2,3,4,5};
var threeFirstNumbers = numbers.Take(3); Console.WriteLine(string.Join(“,”, threeFirstNumbers.ToArray()));
//1,2,3
Section 8.34: Reverse
var numbers = new[] {1,2,3,4,5}; var reversed = numbers.Reverse();
Console.WriteLine(string.Join(“,”, reversed.ToArray()));
//5,4,3,2,1
Section 8.35: OfType
var mixed = new object[] {1,”Foo”,2,”Bar”,3,”Fizz”,4,”Buzz”}; var numbers = mixed.OfType();
Console.WriteLine(string.Join(“,”, numbers.ToArray()));
//1,2,3,4
Section 8.36: Max
var numbers = new[] {1,2,3,4};
var maxNumber = numbers.Max(); Console.WriteLine(maxNumber); //4
var cities = new[] { new {Population = 1000}, new {Population = 2500}, new {Population = 4000} };
var maxPopulation = cities.Max(c => c.Population); Console.WriteLine(maxPopulation); //4000
Section 8.37: Average
var numbers = new[] {1,2,3,4};
var averageNumber = numbers.Average(); Console.WriteLine(averageNumber); // 2,5
This method calculates the average of enumerable of numbers.
var cities = new[] {
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new {Population = 1000}, new {Population = 2000}, new {Population = 4000} };
var averagePopulation = cities.Average(c => c.Population); Console.WriteLine(averagePopulation); // 2333,33
This method calculates the average of enumerable using delegated function.
Section 8.38: GroupBy
var persons = new[] { new { Name=”Fizz”, Job=”Developer”}, new { Name=”Buzz”, Job=”Developer”}, new { Name=”Foo”, Job=”Astronaut”}, new { Name=”Bar”, Job=”Astronaut”}, };
var groupedByJob = persons.GroupBy(p => p.Job);
foreach(var theGroup in groupedByJob) { Console.WriteLine( “{0} are {1}s”, string.Join(“,”, theGroup.Select(g => g.Name).ToArray()), theGroup.Key); }
//Fizz,Buzz are Developers //Foo,Bar are Astronauts
Group invoices by country, generating a new object with the number of record, total paid, and average paid
var a = db.Invoices.GroupBy(i => i.Country) .Select(g => new { Country = g.Key, Count = g.Count(), Total = g.Sum(i => i.Paid), Average = g.Average(i => i.Paid) });
If we want only the totals, no group
var a = db.Invoices.GroupBy(i => 1) .Select(g => new { Count = g.Count(), Total = g.Sum(i => i.Paid), Average = g.Average(i => i.Paid) });
If we need several counts
var a = db.Invoices.GroupBy(g => 1) .Select(g => new { High = g.Count(i => i.Paid >= 1000), Low = g.Count(i => i.Paid i.Paid) });
Section 8.39: ToDictionary
Returns a new dictionary from the source IEnumerable using the provided keySelector function to determine keys.
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Will throw an ArgumentException if keySelector is not injective(returns a unique value for each member of the source collection.) There are overloads which allow one to specify the value to be stored as well as the key.
var persons = new[] { new { Name=”Fizz”, Id=1}, new { Name=”Buzz”, Id=2}, new { Name=”Foo”, Id=3}, new { Name=”Bar”, Id=4}, };
Specifying just a key selector function will create a Dictionary with TKey the return Type of the key selector, TVal the original object Type, and the original object as the stored value.
var personsById = persons.ToDictionary(p => p.Id); // personsById is a Dictionary
Console.WriteLine(personsById[1].Name); //Fizz Console.WriteLine(personsById[2].Name); //Buzz
Specifying a value selector function as well will create a Dictionary with TKey still the return type of the key selector, but TVal now the return type of the value selector function, and the returned value as the stored value.
var namesById = persons.ToDictionary(p => p.Id, p => p.Name); //namesById is a Dictionary
Console.WriteLine(namesById[3]); //Foo Console.WriteLine(namesById[4]); //Bar
As stated above, the keys returned by the key selector must be unique. The following will throw an exception.
var persons = new[] { new { Name=”Fizz”, Id=1}, new { Name=”Buzz”, Id=2}, new { Name=”Foo”, Id=3}, new { Name=”Bar”, Id=4}, new { Name=”Oops”, Id=4} };
var willThrowException = persons.ToDictionary(p => p.Id)
If a unique key can not be given for the source collection, consider using ToLookup instead. On the surface, ToLookup behaves similarly to ToDictionary, however, in the resulting Lookup each key is paired with a collection of values with matching keys.
Section 8.40: Union
var numbers1to5 = new[] {1,2,3,4,5}; var numbers4to8 = new[] {4,5,6,7,8};
var numbers1to8 = numbers1to5.Union(numbers4to8);
Console.WriteLine(string.Join(“,”, numbers1to8));
//1,2,3,4,5,6,7,8
Note that duplicates are removed from the result. If this is undesirable, use Concat instead.
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Section 8.41: ToArray
var numbers = new[] {1,2,3,4,5,6,7,8,9,10}; var someNumbers = numbers.Where(n => n n (n & 1) == 0);
Console.WriteLine(string.Join(“,”, oddNumbers.ToArray()));
//1,3,5,7
Section 8.46: TakeWhile
var numbers = new[] {2,4,6,1,3,5,7,8};
var evenNumbers = numbers.TakeWhile(n => (n & 1) == 0);
Console.WriteLine(string.Join(“,”, evenNumbers.ToArray()));
//2,4,6
Section 8.47: DefaultIfEmpty
var numbers = new[] {2,4,6,8,1,3,5,7};
var numbersOrDefault = numbers.DefaultIfEmpty(); Console.WriteLine(numbers.SequenceEqual(numbersOrDefault)); //True
var noNumbers = new int[0];
var noNumbersOrDefault = noNumbers.DefaultIfEmpty(); Console.WriteLine(noNumbersOrDefault.Count()); //1 Console.WriteLine(noNumbersOrDefault.Single()); //0
var noNumbersOrExplicitDefault = noNumbers.DefaultIfEmpty(34); Console.WriteLine(noNumbersOrExplicitDefault.Count()); //1 Console.WriteLine(noNumbersOrExplicitDefault.Single()); //34
Section 8.48: Join
class Developer { public int Id { get; set; } public string Name { get; set; } }
class Project { public int DeveloperId { get; set; } public string Name { get; set; } }
var developers = new[] { new Developer { Id = 1, Name = “Foobuzz” }, new Developer { Id = 2, Name = “Barfizz” } };
var projects = new[] {
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new Project { DeveloperId = 1, Name = “Hello World 3D” }, new Project { DeveloperId = 1, Name = “Super Fizzbuzz Maker” }, new Project { DeveloperId = 2, Name = “Citizen Kane – The action game” }, new Project { DeveloperId = 2, Name = “Pro Pong 2016” } };
var denormalized = developers.Join( inner: projects, outerKeySelector: dev => dev.Id, innerKeySelector: proj => proj.DeveloperId, resultSelector: (dev, proj) => new { ProjectName = proj.Name, DeveloperName = dev.Name}); foreach(var item in denormalized) { Console.WriteLine(“{0} by {1}”, item.ProjectName, item.DeveloperName); }
//Hello World 3D by Foobuzz //Super Fizzbuzz Maker by Foobuzz //Citizen Kane – The action game by Barfizz //Pro Pong 2016 by Barfizz
Section 8.49: Left Outer Join
class Person { public string FirstName { get; set; } public string LastName { get; set; } }
class Pet { public string Name { get; set; } public Person Owner { get; set; } }
public static void Main(string[] args) { var magnus = new Person { FirstName = “Magnus”, LastName = “Hedlund” }; var terry = new Person { FirstName = “Terry”, LastName = “Adams” };
var barley = new Pet { Name = “Barley”, Owner = terry };
var people = new[] { magnus, terry }; var pets = new[] { barley };
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var query = from person in people join pet in pets on person equals pet.Owner into gj from subpet in gj.DefaultIfEmpty() select new { person.FirstName, PetName = subpet?.Name ?? “-” // Use – if he has no pet };
foreach (var p in query) Console.WriteLine($”{p.FirstName}: {p.PetName}”); }
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Chapter 9: ForEach Section 9.1: Extension method for IEnumerable
ForEach() is defined on the List class, but not on IQueryable or IEnumerable. You have two choices in those cases:
ToList first
The enumeration (or query) will be evaluated, copying the results into a new list or calling the database. The method is then called on each item.
IEnumerable customers = new List();
customers.ToList().ForEach(c => c.SendEmail());
This method has obvious memory usage overhead, as an intermediate list is created.
Extension method
Write an extension method:
public static void ForEach(this IEnumerable enumeration, Action action) { foreach(T item in enumeration) { action(item); } }
Use:
IEnumerable customers = new List();
customers.ForEach(c => c.SendEmail());
Caution: The Framework’s LINQ methods have been designed with the intention of being pure, which means they do not produce side effects. The ForEach method’s only purpose is to produce side effects, and deviates from the other methods in this aspect. You may consider just using a plain foreach loop instead.
Section 9.2: Calling a method on an object in a list
public class Customer { public void SendEmail() { // Sending email code here } }
List customers = new List();
customers.Add(new Customer()); customers.Add(new Customer());
customers.ForEach(c => c.SendEmail());
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Chapter 10: Reflection Section 10.1: What is an Assembly?
Assemblies are the building block of any Common Language Runtime (CLR) application. Every type you define, together with its methods, properties and their bytecode, is compiled and packaged inside an Assembly.
using System.Reflection;
Assembly assembly = this.GetType().Assembly;
Assemblies are self-documenting: they do not only contain types, methods and their IL code, but also the Metadata necessary to inspect and consume them, both at compile and runtime:
Assembly assembly = Assembly.GetExecutingAssembly();
foreach (var type in assembly.GetTypes()) { Console.WriteLine(type.FullName); }
Assemblies have names which describes their full, unique identity:
Console.WriteLine(typeof(int).Assembly.FullName); // Will print: “mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089”
If this name includes a PublicKeyToken, it is called a strong name. Strong-naming an assembly is the process of creating a signature by using the private key that corresponds to the public key distributed with the assembly. This signature is added to the Assembly manifest, which contains the names and hashes of all the files that make up the assembly, and its PublicKeyToken becomes part of the name. Assemblies that have the same strong name should be identical; strong names are used in versioning and to prevent assembly conflicts.
Section 10.2: Compare two objects with reflection
public class Equatable { public string field1;
public override bool Equals(object obj) { if (ReferenceEquals(null, obj)) return false; if (ReferenceEquals(this, obj)) return true;
var type = obj.GetType(); if (GetType() != type) return false;
var fields = type.GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public); foreach (var field in fields) if (field.GetValue(this) != field.GetValue(obj)) return false;
return true; }
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public override int GetHashCode() { var accumulator = 0; var fields = GetType().GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public); foreach (var field in fields) accumulator = unchecked ((accumulator * 937) ^ field.GetValue(this).GetHashCode());
return accumulator; } }
Note: this example do a field based comparasion (ignore static fields and properties) for simplicity Section 10.3: Creating Object and setting properties using reflection
Lets say we have a class Classy that has property Propertua
public class Classy { public string Propertua {get; set;} }
to set Propertua using reflection:
var typeOfClassy = typeof (Classy); var classy = new Classy(); var prop = typeOfClassy.GetProperty(“Propertua”); prop.SetValue(classy, “Value”);
Section 10.4: How to create an object of T using Reflection
Using the default constructor
T variable = Activator.CreateInstance(typeof(T));
Using parameterized constructor
T variable = Activator.CreateInstance(typeof(T), arg1, arg2);
Section 10.5: Getting an attribute of an enum with reflection (and caching it)
Attributes can be useful for denoting metadata on enums. Getting the value of this can be slow, so it is important to cache results.
private static Dictionary attributeCache = new Dictionary();
public static T GetAttribute(this V value) where T : Attribute where V : struct { object temp;
// Try to get the value from the static cache.
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if (attributeCache.TryGetValue(value, out temp)) { return (T) temp; } else { // Get the type of the struct passed in. Type type = value.GetType(); FieldInfo fieldInfo = type.GetField(value.ToString());
// Get the custom attributes of the type desired found on the struct. T[] attribs = (T[])fieldInfo.GetCustomAttributes(typeof(T), false);
// Return the first if there was a match. var result = attribs.Length > 0 ? attribs[0] : null;
// Cache the result so future checks won’t need reflection. attributeCache.Add(value, result);
return result; } }
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Chapter 11: Expression Trees Section 11.1: building a predicate of form field == value
To build up an expression like _ => _.Field == “VALUE” at runtime.
Given a predicate _ => _.Field and a string value “VALUE”, create an expression that tests whether or not the predicate is true.
The expression is suitable for:
IQueryable, IEnumerable to test the predicate. entity framework or Linq to SQL to create a Where clause that tests the predicate.
This method will build an appropriate Equal expression that tests whether or not Field equals “VALUE”.
public static Expression<Func> BuildEqualPredicate( Expression<Func> memberAccessor, string term) { var toString = Expression.Convert(Expression.Constant(term), typeof(string)); Expression expression = Expression.Equal(memberAccessor.Body, toString); var predicate = Expression.Lambda<Func>( expression, memberAccessor.Parameters); return predicate; }
The predicate can be used by including the predicate in a Where extension method.
var predicate = PredicateExtensions.BuildEqualPredicate( _ => _.Field, “VALUE”); var results = context.Entity.Where(predicate).ToList();
Section 11.2: Simple Expression Tree Generated by the C# Compiler
Consider the following C# code
Expression<Func> expression = a => a + 1;
Because the C# compiler sees that the lambda expression is assigned to an Expression type rather than a delegate type it generates an expression tree roughly equivalent to this code
ParameterExpression parameterA = Expression.Parameter(typeof(int), “a”); var expression = (Expression<Func>)Expression.Lambda( Expression.Add( parameterA, Expression.Constant(1)), parameterA);
The root of the tree is the lambda expression which contains a body and a list of parameters. The lambda has 1 parameter called “a”. The body is a single expression of CLR type BinaryExpression and NodeType of Add. This expression represents addition. It has two subexpressions denoted as Left and Right. Left is the
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ParameterExpression for the parameter “a” and Right is a ConstantExpression with the value 1.
The simplest usage of this expression is printing it:
Console.WriteLine(expression); //prints a => (a + 1)
Which prints the equivalent C# code.
The expression tree can be compiled into a C# delegate and executed by the CLR
Func lambda = expression.Compile(); Console.WriteLine(lambda(2)); //prints 3
Usually expressions are translated to other languages like SQL, but can be also used to invoke private, protected and internal members of public or non-public types as alternative to Reflection.
Section 11.3: Expression for retrieving a static field
Having example type like this:
public TestClass { public static string StaticPublicField = “StaticPublicFieldValue”; }
We can retrieve value of StaticPublicField:
var fieldExpr = Expression.Field(null, typeof(TestClass), “StaticPublicField”); var labmda = Expression.Lambda<Func>(fieldExpr);
It can be then i.e. compiled into a delegate for retrieving field value.
Func retriever = lambda.Compile(); var fieldValue = retriever();
//fieldValue result is StaticPublicFieldValue
Section 11.4: InvocationExpression Class
InvocationExpression class allows invocation of other lambda expressions that are parts of the same Expression tree.
You create them with static Expression.Invoke method.
Problem We want to get on the items which have “car” in their description. We need to check it for null before searching for a string inside but we don’t want it to be called excessively, as the computation could be expensive.
using System; using System.Linq; using System.Linq.Expressions; public class Program { public static void Main() { var elements = new[] {
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new Element { Description = “car” }, new Element { Description = “cargo” }, new Element { Description = “wheel” }, new Element { Description = null }, new Element { Description = “Madagascar” }, }; var elementIsInterestingExpression = CreateSearchPredicate( searchTerm: “car”, whereToSearch: (Element e) => e.Description); Console.WriteLine(elementIsInterestingExpression.ToString()); var elementIsInteresting = elementIsInterestingExpression.Compile(); var interestingElements = elements.Where(elementIsInteresting); foreach (var e in interestingElements) { Console.WriteLine(e.Description); } var countExpensiveComputations = 0; Action incCount = () => countExpensiveComputations++; elements .Where( CreateSearchPredicate( “car”, (Element e) => ExpensivelyComputed( e, incCount ) ).Compile() ) .Count(); Console.WriteLine(“Property extractor is called {0} times.”, countExpensiveComputations); } private class Element { public string Description { get; set; } } private static string ExpensivelyComputed(Element source, Action count) { count(); return source.Description; } private static Expression<Func> CreateSearchPredicate( string searchTerm, Expression<Func> whereToSearch) { var extracted = Expression.Parameter(typeof(string), “extracted”); Expression<Func> coalesceNullCheckWithSearch = Expression.Lambda<Func>( Expression.AndAlso( Expression.Not( Expression.Call(typeof(string), “IsNullOrEmpty”, null, extracted) ), Expression.Call(extracted, “Contains”, null, Expression.Constant(searchTerm)) ), extracted);
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var elementParameter = Expression.Parameter(typeof(T), “element”); return Expression.Lambda<Func>( Expression.Invoke( coalesceNullCheckWithSearch, Expression.Invoke(whereToSearch, elementParameter) ), elementParameter ); } }
Output
element => Invoke(extracted => (Not(IsNullOrEmpty(extracted)) AndAlso extracted.Contains(“car”)), Invoke(e => e.Description, element)) car cargo Madagascar Predicate is called 5 times.
First thing to note is how the actual propery access, wrapped in an Invoke:
Invoke(e => e.Description, element)
, and this is the only part that touches e.Description, and in place of it, extracted parameter of type string is passed to the next one:
(Not(IsNullOrEmpty(extracted)) AndAlso extracted.Contains(“car”))
Another important thing to note here is AndAlso. It computes only the left part, if the first part returns ‘false’. It’s a common mistake to use the bitwise operator ‘And’ instead of it, which always computes both parts, and would fail with a NullReferenceException in this example.
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Chapter 12: Custom Types Section 12.1: Struct Definition Structs inherit from System.ValueType, are value types, and live on the stack. When value types are passed as a parameter, they are passed by value. Struct MyStruct { public int x; public int y; }
Passed by value means that the value of the parameter is copied for the method, and any changes made to the parameter in the method are not reflected outside of the method. For instance, consider the following code, which calls a method named AddNumbers, passing in the variables a and b, which are of type int, which is a Value type.
int a = 5; int b = 6;
AddNumbers(a,b);
public AddNumbers(int x, int y) { int z = x + y; // z becomes 11 x = x + 5; // now we changed x to be 10 z = x + y; // now z becomes 16 }
Even though we added 5 to x inside the method, the value of a remains unchanged, because it’s a Value type, and that means x was a copy of a’s value, but not actually a.
Remember, Value types live on the stack, and are passed by value.
Section 12.2: Class Definition Classes inherit from System.Object, are reference types, and live on the heap. When reference types are passed as a parameter, they are passed by reference. public Class MyClass { public int a; public int b; }
Passed by reference means that a reference to the parameter is passed to the method, and any changes to the parameter will be reflected outside of the method when it returns, because the reference is to the exact same object in memory. Let’s use the same example as before, but we’ll “wrap” the ints in a class first.
MyClass instanceOfMyClass = new MyClass(); instanceOfMyClass.a = 5; instanceOfMyClass.b = 6;
AddNumbers(instanceOfMyClass);
public AddNumbers(MyClass sample) {
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int z = sample.a + sample.b; // z becomes 11 sample.a = sample.a + 5; // now we changed a to be 10 z = sample.a + sample.b; // now z becomes 16 }
This time, when we changed sample.a to 10, the value of instanceOfMyClass.a also changes, because it was passed by reference. Passed by reference means that a reference (also sometimes called a pointer) to the object was passed into the method, instead of a copy of the object itself.
Remember, Reference types live on the heap, and are passed by reference.
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Chapter 13: Code Contracts Section 13.1: Contracts for Interfaces
Using Code Contracts it is possible to apply a contract to an interface. This is done by declaring an abstract class that implments the interfaces. The interface should be tagged with the ContractClassAttribute and the contract definition (the abstract class) should be tagged with the ContractClassForAttribute
C# Example…
[ContractClass(typeof(MyInterfaceContract))] public interface IMyInterface { string DoWork(string input); } //Never inherit from this contract defintion class [ContractClassFor(typeof(IMyInterface))] internal abstract class MyInterfaceContract : IMyInterface { private MyInterfaceContract() { }
public string DoWork(string input) { Contract.Requires(!string.IsNullOrEmpty(input)); Contract.Ensures(!string.IsNullOrEmpty(Contract.Result())); throw new NotSupportedException(); } } public class MyInterfaceImplmentation : IMyInterface { public string DoWork(string input) { return input; } }
Static Analysis Result…
Section 13.2: Installing and Enabling Code Contracts
While System.Diagnostics.Contracts is included within the .Net Framework. To use Code Contracts you must install the Visual Studio extensions.
Under Extensions and Updates search for Code Contracts then install the Code Contracts Tools
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After the tools are installed you must enable Code Contracts within your Project solution. At the minimum you probably want to enable the Static Checking (check after build). If you are implementing a library that will be used by other solutions you may want to consider also enabling Runtime Checking.
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Section 13.3: Preconditions
Preconditions allows methods to provide minimum required values for input parameters
Example…
void DoWork(string input) { Contract.Requires(!string.IsNullOrEmpty(input));
//do work }
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Static Analysis Result…
Section 13.4: Postconditions
Postconditions ensure that the returned results from a method will match the provided definition. This provides the caller with a definition of the expected result. Postconditions may allowed for simplied implmentations as some possible outcomes can be provided by the static analyizer.
Example…
string GetValue() { Contract.Ensures(Contract.Result() != null);
return null; }
Static Analyis Result…
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Chapter 14: Settings Section 14.1: AppSettings from ConfigurationSettings in .NET 1.x Deprecated usage
The ConfigurationSettings class was the original way to retrieve settings for an assembly in .NET 1.0 and 1.1. It has been superseded by the ConfigurationManager class and the WebConfigurationManager class.
If you have two keys with the same name in the appSettings section of the configuration file, the last one is used.
app.config

Program.cs
using System; using System.Configuration; using System.Diagnostics;
namespace ConsoleApplication1 { class Program { static void Main() { string keyValue = ConfigurationSettings.AppSettings[“keyName”]; Debug.Assert(“anything, as a string”.Equals(keyValue));
string twoKeys = ConfigurationSettings.AppSettings[“keyNames”]; Debug.Assert(“234”.Equals(twoKeys));
Console.ReadKey(); } } }
Section 14.2: Reading AppSettings from ConfigurationManager in .NET 2.0 and later
The ConfigurationManager class supports the AppSettings property, which allows you to continue reading settings from the appSettings section of a configuration file the same way as .NET 1.x supported.
app.config

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Program.cs
using System; using System.Configuration; using System.Diagnostics;
namespace ConsoleApplication1 { class Program { static void Main() { string keyValue = ConfigurationManager.AppSettings[“keyName”]; Debug.Assert(“anything, as a string”.Equals(keyValue));
var twoKeys = ConfigurationManager.AppSettings[“keyNames”]; Debug.Assert(“234”.Equals(twoKeys));
Console.ReadKey(); } } }
Section 14.3: Introduction to strongly-typed application and user settings support from Visual Studio
Visual Studio helps manage user and application settings. Using this approach has these benefits over using the appSettings section of the configuration file.
1.
Settings can be made strongly typed. Any type which can be serialized can be used for a settings value.
2.
Application settings can be easily separated from user settings. Application settings are stored in a single configuration file: web.config for Web sites and Web applications, and app.config, renamed as assembly.exe.config, where assembly is the name of the executable. User settings (not used by Web projects) are stored in a user.config file in the user’s Application Data folder (which varies with the operating system version).
3.
Application settings from class libraries can be combined into a single configuration file without risk of name collisions, since each class library can have its own custom settings section.
In most project types, the Project Properties Designer has a Settings tab which is the starting point for creating custom application and user settings. Initially, the Settings tab will be blank, with a single link to create a default settings file. Clicking the link results in these changes:
1.
If a configuration file (app.config or web.config) does not exist for the project, one will be created.
2.
The Settings tab will be replaced with a grid control which enables you to create, edit, and delete individual settings entries.
3.
In Solution Explorer, a Settings.settings item is added under the Properties special folder. Opening this
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item will open the Settings tab.
4.
A new file with a new partial class is added under the Properties folder in the project folder. This new file is named Settings.Designer.__ (.cs, .vb, etc.), and the class is named Settings. The class is code-generated, so it should not be edited, but the class is a partial class, so you can extend the class by putting additional members in a separate file. Furthermore, the class is implemented using the Singleton Pattern, exposing the singleton instance with the property named Default.
As you add each new entry to the Settings tab, Visual Studio does these two things:
1.
2.
Saves the setting in the configuration file, in a custom configuration section designed to be managed by the Settings class.
Creates a new member in the Settings class to read, write, and present the setting in the specific type selected from the Settings tab.
Section 14.4: Reading strongly-typed settings from custom section of configuration file
Starting from a new Settings class and custom configuration section:
Add an application setting named ExampleTimeout, using the time System.Timespan, and set the value to 1 minute:
Save the Project Properties, which saves the Settings tab entries, as well as re-generates the custom Settings class and updates the project configuration file.
Use the setting from code (C#):
Program.cs
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using System; using System.Diagnostics; using ConsoleApplication1.Properties;
namespace ConsoleApplication1 { class Program { static void Main() { TimeSpan exampleTimeout = Settings.Default.ExampleTimeout; Debug.Assert(TimeSpan.FromMinutes(1).Equals(exampleTimeout));
Console.ReadKey(); } } }
Under the covers
Look in the project configuration file to see how the application setting entry has been created:
app.config (Visual Studio updates this automatically)

00:01:00
Notice that the appSettings section is not used. The applicationSettings section contains a custom namespace- qualified section that has a setting element for each entry. The type of the value is not stored in the configuration file; it is only known by the Settings class.
Look in the Settings class to see how it uses the ConfigurationManager class to read this custom section.
Settings.designer.cs (for C# projects)
… [global::System.Configuration.ApplicationScopedSettingAttribute()] [global::System.Diagnostics.DebuggerNonUserCodeAttribute()] [global::System.Configuration.DefaultSettingValueAttribute(“00:01:00”)] public global::System.TimeSpan ExampleTimeout { get { return ((global::System.TimeSpan)(this[“ExampleTimeout”]));
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} } …
Notice that a DefaultSettingValueAttribute was created to stored the value entered in the Settings tab of the Project Properties Designer. If the entry is missing from the configuration file, this default value is used instead.
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Chapter 15: Regular Expressions (System.Text.RegularExpressions) Section 15.1: Check if pattern matches input
public bool Check() { string input = “Hello World!”; string pattern = @”H.ll. W.rld!”;
// true return Regex.IsMatch(input, pattern); }
Section 15.2: Remove non alphanumeric characters from string
public string Remove() { string input = “Hello./!”; return Regex.Replace(input, “[^a-zA-Z0-9]”, “”); }
Section 15.3: Passing Options
public bool Check() { string input = “Hello World!”; string pattern = @”H.ll. W.rld!”;
// true return Regex.IsMatch(input, pattern, RegexOptions.IgnoreCase | RegexOptions.Singleline); }
Section 15.4: Match into groups
public string Check() { string input = “Hello World!”; string pattern = @”H.ll. (?W.rld)!”;
Match match = Regex.Match(input, pattern);
// World return match.Groups[“Subject”].Value; }
Section 15.5: Find all matches Using using System.Text.RegularExpressions; Code
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static void Main(string[] args) { string input = “Carrot Banana Apple Cherry Clementine Grape”; // Find words that start with uppercase ‘C’ string pattern = @”bCw*b”;
MatchCollection matches = Regex.Matches(input, pattern); foreach (Match m in matches) Console.WriteLine(m.Value); } Output Carrot Cherry Clementine
Section 15.6: Simple match and replace
public string Check() { string input = “Hello World!”; string pattern = @”W.rld”;
// Hello Stack Overflow! return Regex.Replace(input, pattern, “Stack Overflow”); }
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Chapter 16: File Input/Output
Parameter string path Path of the file to check. (relative or fully qualified)
Details
Section 16.1: C# File.Exists()
using System; using System.IO; public class Program { public static void Main() { string filePath = “somePath”; if(File.Exists(filePath)) { Console.WriteLine(“Exists”); } else { Console.WriteLine(“Does not exist”); } } }
Can also be used in a ternary operator.
Console.WriteLine(File.Exists(pathToFile) ? “Exists” : “Does not exist”);
Section 16.2: VB WriteAllText
Imports System.IO
Dim filename As String = “c:pathtofile.txt” File.WriteAllText(filename, “Text to write” & vbCrLf)
Section 16.3: VB StreamWriter
Dim filename As String = “c:pathtofile.txt” If System.IO.File.Exists(filename) Then Dim writer As New System.IO.StreamWriter(filename) writer.Write(“Text to write” & vbCrLf) ‘Add a newline writer.close() End If
Section 16.4: C# StreamWriter
using System.Text; using System.IO;
string filename = “c:pathtofile.txt”; //’using’ structure allows for proper disposal of stream. using (StreamWriter writer = new StreamWriter(filename”))
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{ writer.WriteLine(“Text to Writen”); }
Section 16.5: C# WriteAllText()
using System.IO; using System.Text;
string filename = “c:pathtofile.txt”; File.writeAllText(filename, “Text to writen”);
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Chapter 17: System.IO Section 17.1: Reading a text file using StreamReader
string fullOrRelativePath = “testfile.txt”;
string fileData;
using (var reader = new StreamReader(fullOrRelativePath)) { fileData = reader.ReadToEnd(); }
Note that this StreamReader constructor overload does some auto encoding detection, which may or may not conform to the actual encoding used in the file.
Please note that there are some convenience methods that read all text from file available on the System.IO.File class, namely File.ReadAllText(path) and File.ReadAllLines(path).
Section 17.2: Serial Ports using System.IO.SerialPorts Iterating over connected serial ports using System.IO.Ports; string[] ports = SerialPort.GetPortNames(); for (int i = 0; i !String.IsNullOrWhiteSpace(x)));
If file is too big to load it in memory and output path is different from input path:
File.WriteAllLines(outputPath, File.ReadLines(inputPath).Where(x => !String.IsNullOrWhiteSpace(x)));
Section 18.3: Convert text file encoding
Text is saved encoded (see also Strings topic) then sometimes you may need to change its encoding, this example assumes (for simplicity) that file is not too big and it can be entirely read in memory:
public static void ConvertEncoding(string path, Encoding from, Encoding to) { File.WriteAllText(path, File.ReadAllText(path, from), to); }
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When performing conversions do not forget that file may contain BOM (Byte Order Mark), to better understand how it’s managed refer to Encoding.UTF8.GetString doesn’t take into account the Preamble/BOM.
Section 18.4: Enumerate files older than a specified amount
This snippet is an helper function to enumerate all files older than a specified age, it’s useful – for example – when you have to delete old log files or old cached data.
static IEnumerable EnumerateAllFilesOlderThan( TimeSpan maximumAge, string path, string searchPattern = “*.*”, SearchOption options = SearchOption.TopDirectoryOnly) { DateTime oldestWriteTime = DateTime.Now – maximumAge;
return Directory.EnumerateFiles(path, searchPattern, options) .Where(x => Directory.GetLastWriteTime(x) < oldestWriteTime); }
Used like this:
var oldFiles = EnumerateAllFilesOlderThan(TimeSpan.FromDays(7), @"c:log", "*.log");
Few things to note:
Search is performed using Directory.EnumerateFiles() instead of Directory.GetFiles(). Enumeration is alive then you won't need to wait until all file system entries have been fetched. We're checking for last write time but you may use creation time or last access time (for example to delete unused cached files, note that access time may be disabled). Granularity isn't uniform for all those properties (write time, access time, creation time), check MSDN for details about this.
Section 18.5: Move a File from one location to another File.Move In order to move a file from one location to another, one simple line of code can achieve this:
File.Move(@"C:TemporaryFile.txt", @"C:TemporaryFilesTemporaryFile.txt");
However, there are many things that could go wrong with this simple operation. For instance, what if the user running your program does not have a Drive that is labelled 'C'? What if they did – but they decided to rename it to 'B', or 'M'?
What if the Source file (the file in which you would like to move) has been moved without your knowing – or what if it simply doesn't exist.
This can be circumvented by first checking to see whether the source file does exist:
string source = @"C:TemporaryFile.txt", destination = @"C:TemporaryFilesTemporaryFile.txt"; if(File.Exists("C:TemporaryFile.txt")) { File.Move(source, destination); }
This will ensure that at that very moment, the file does exist, and can be moved to another location. There may be
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times where a simple call to File.Exists won't be enough. If it isn't, check again, convey to the user that the operation failed – or handle the exception.
A FileNotFoundException is not the only exception you are likely to encounter.
See below for possible exceptions:
Exception Type
IOException ArgumentNullException
ArgumentException
Description
The file already exists or the source file could not be found. The value of the Source and/or Destination parameters is null. The value of the Source and/or Destination parameters are empty, or contain invalid characters.
UnauthorizedAccessException You do not have the required permissions in order to perform this action.
PathTooLongException
The Source, Destination or specified path(s) exceed the maximum length. On Windows, a Path's length must be less than 248 characters, while File names must be less than 260 characters.
DirectoryNotFoundException The specified directory could not be found. NotSupportedException
The Source or Destination paths or file names are in an invalid format.
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Chapter 19: Reading and writing Zip files
The ZipFile class lives in the System.IO.Compression namespace. It can be used to read from, and write to Zip files.
Section 19.1: Listing ZIP contents
This snippet will list all the filenames of a zip archive. The filenames are relative to the zip root.
using (FileStream fs = new FileStream("archive.zip", FileMode.Open)) using (ZipArchive archive = new ZipArchive(fs, ZipArchiveMode.Read)) { for (int i = 0; i f.Name == “test.txt”)?.ExtractToFile(“test_extracted_linq.txt”, true);
// This will throw a System.ArgumentNullException because the file cannot be found archive.GetEntry(“nonexistingfile.txt”).ExtractToFile(“fail.txt”, true); }
Any of these methods will produce the same result.
Section 19.3: Updating a ZIP file
To update a ZIP file, the file has to be opened with ZipArchiveMode.Update instead.
using (FileStream fs = new FileStream(“archive.zip”, FileMode.Open))
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using (ZipArchive archive = new ZipArchive(fs, ZipArchiveMode.Update)) { // Add file to root archive.CreateEntryFromFile(“test.txt”, “test.txt”);
// Add file to subfolder archive.CreateEntryFromFile(“test.txt”, “symbols/test.txt”); }
There is also the option to write directly to a file within the archive:
var entry = archive.CreateEntry(“createentry.txt”); using(var writer = new StreamWriter(entry.Open())) { writer.WriteLine(“Test line”); }
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Chapter 20: Managed Extensibility Framework Section 20.1: Connecting (Basic)
See the other (Basic) examples above.
using System.ComponentModel.Composition; using System.ComponentModel.Composition.Hosting;
namespace Demo { public static class Program { public static void Main() { using (var catalog = new ApplicationCatalog()) using (var exportProvider = new CatalogExportProvider(catalog)) using (var container = new CompositionContainer(exportProvider)) { exportProvider.SourceProvider = container;
UserWriter writer = new UserWriter();
// at this point, writer’s userProvider field is null container.ComposeParts(writer);
// now, it should be non-null (or an exception will be thrown). writer.PrintAllUsers(); } } } }
As long as something in the application’s assembly search path has [Export(typeof(IUserProvider))], UserWriter’s corresponding import will be satisfied and the users will be printed.
Other types of catalogs (e.g., DirectoryCatalog) can be used instead of (or in addition to) ApplicationCatalog, to look in other places for exports that satisfy the imports.
Section 20.2: Exporting a Type (Basic)
using System.Collections.Generic; using System.Collections.ObjectModel; using System.ComponentModel.Composition;
namespace Demo { [Export(typeof(IUserProvider))] public sealed class UserProvider : IUserProvider { public ReadOnlyCollection GetAllUsers() { return new List { new User(0, “admin”), new User(1, “Dennis”),
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new User(2, “Samantha”), }.AsReadOnly(); } } }
This could be defined virtually anywhere; all that matters is that the application knows where to look for it (via the ComposablePartCatalogs it creates).
Section 20.3: Importing (Basic)
using System; using System.ComponentModel.Composition;
namespace Demo { public sealed class UserWriter { [Import(typeof(IUserProvider))] private IUserProvider userProvider;
public void PrintAllUsers() { foreach (User user in this.userProvider.GetAllUsers()) { Console.WriteLine(user); } } } }
This is a type that has a dependency on an IUserProvider, which could be defined anywhere. Like the previous example, all that matters is that the application knows where to look for the matching export (via the ComposablePartCatalogs it creates).
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Chapter 21: SpeechRecognitionEngine class to recognize speech
LoadGrammar: Parameters
grammar
RecognizeAsync: Parameters
mode
Details
The grammar to load. For example, a DictationGrammar object to allow free text dictation. Details The RecognizeMode for the current recognition: Single for just one recognition, Multiple to allow multiple.
GrammarBuilder.Append: Parameters Details
choices
Choices constructor: Parameters choices Grammar constructor: Parameter builder
Appends some choices to the grammar builder. This means that, when the user inputs speech, the recognizer can follow different “branches” from a grammar. Details An array of choices for the grammar builder. See GrammarBuilder.Append. Details The GrammarBuilder to construct a Grammar from.
Section 21.1: Asynchronously recognizing speech based on a restricted set of phrases
SpeechRecognitionEngine recognitionEngine = new SpeechRecognitionEngine(); GrammarBuilder builder = new GrammarBuilder(); builder.Append(new Choices(“I am”, “You are”, “He is”, “She is”, “We are”, “They are”)); builder.Append(new Choices(“friendly”, “unfriendly”)); recognitionEngine.LoadGrammar(new Grammar(builder)); recognitionEngine.SpeechRecognized += delegate(object sender, SpeechRecognizedEventArgs e) { Console.WriteLine(“You said: {0}”, e.Result.Text); }; recognitionEngine.SetInputToDefaultAudioDevice(); recognitionEngine.RecognizeAsync(RecognizeMode.Multiple);
Section 21.2: Asynchronously recognizing speech for free text dictation
using System.Speech.Recognition;
// …
SpeechRecognitionEngine recognitionEngine = new SpeechRecognitionEngine(); recognitionEngine.LoadGrammar(new DictationGrammar()); recognitionEngine.SpeechRecognized += delegate(object sender, SpeechRecognizedEventArgs e) { Console.WriteLine(“You said: {0}”, e.Result.Text); }; recognitionEngine.SetInputToDefaultAudioDevice(); recognitionEngine.RecognizeAsync(RecognizeMode.Multiple);
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Chapter 22: System.Runtime.Caching.MemoryCache (ObjectCache) Section 22.1: Adding Item to Cache (Set)
Set function inserts a cache entry into the cache by using a CacheItem instance to supply the key and value for the cache entry.
This function Overrides ObjectCache.Set(CacheItem, CacheItemPolicy)
private static bool SetToCache() { string key = “Cache_Key”; string value = “Cache_Value”;
//Get a reference to the default MemoryCache instance. var cacheContainer = MemoryCache.Default;
var policy = new CacheItemPolicy() { AbsoluteExpiration = DateTimeOffset.Now.AddMinutes(DEFAULT_CACHE_EXPIRATION_MINUTES) }; var itemToCache = new CacheItem(key, value); //Value is of type object. cacheContainer.Set(itemToCache, policy); }
Section 22.2: System.Runtime.Caching.MemoryCache (ObjectCache)
This function gets existing item form cache, and if the item don’t exist in cache, it will fetch item based on the valueFetchFactory function.
public static TValue GetExistingOrAdd(string key, double minutesForExpiration, Func valueFetchFactory) { try { //The Lazy class provides Lazy initialization which will evaluate //the valueFetchFactory only if item is not in the cache. var newValue = new Lazy(valueFetchFactory);
//Setup the cache policy if item will be saved back to cache. CacheItemPolicy policy = new CacheItemPolicy() { AbsoluteExpiration = DateTimeOffset.Now.AddMinutes(minutesForExpiration) };
//returns existing item form cache or add the new value if it does not exist. var cachedItem = _cacheContainer.AddOrGetExisting(key, newValue, policy) as Lazy;
return (cachedItem ?? newValue).Value; } catch (Exception excep) {
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return default(TValue); } }
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Chapter 23: System.Reflection.Emit namespace Section 23.1: Creating an assembly dynamically
using System; using System.Reflection; using System.Reflection.Emit;
class DemoAssemblyBuilder { public static void Main() { // An assembly consists of one or more modules, each of which // contains zero or more types. This code creates a single-module // assembly, the most common case. The module contains one type, // named “MyDynamicType”, that has a private field, a property // that gets and sets the private field, constructors that // initialize the private field, and a method that multiplies // a user-supplied number by the private field value and returns // the result. In C# the type might look like this: /* public class MyDynamicType { private int m_number;
public MyDynamicType() : this(42) {} public MyDynamicType(int initNumber) { m_number = initNumber; }
public int Number { get { return m_number; } set { m_number = value; } }
public int MyMethod(int multiplier) { return m_number * multiplier; } } */
AssemblyName aName = new AssemblyName(“DynamicAssemblyExample”); AssemblyBuilder ab = AppDomain.CurrentDomain.DefineDynamicAssembly( aName, AssemblyBuilderAccess.RunAndSave);
// For a single-module assembly, the module name is usually // the assembly name plus an extension. ModuleBuilder mb = ab.DefineDynamicModule(aName.Name, aName.Name + “.dll”);
TypeBuilder tb = mb.DefineType( “MyDynamicType”, TypeAttributes.Public);
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// Add a private field of type int (Int32). FieldBuilder fbNumber = tb.DefineField( “m_number”, typeof(int), FieldAttributes.Private);
// Next, we make a simple sealed method. MethodBuilder mbMyMethod = tb.DefineMethod( “MyMethod”, MethodAttributes.Public, typeof(int), new[] { typeof(int) });
ILGenerator il = mbMyMethod.GetILGenerator(); il.Emit(OpCodes.Ldarg_0); // Load this – always the first argument of any instance method il.Emit(OpCodes.Ldfld, fbNumber); il.Emit(OpCodes.Ldarg_1); // Load the integer argument il.Emit(OpCodes.Mul); // Multiply the two numbers with no overflow checking il.Emit(OpCodes.Ret); // Return
// Next, we build the property. This involves building the property itself, as well as the // getter and setter methods. PropertyBuilder pbNumber = tb.DefineProperty( “Number”, // Name PropertyAttributes.None, typeof(int), // Type of the property new Type[0]); // Types of indices, if any
MethodBuilder mbSetNumber = tb.DefineMethod( “set_Number”, // Name – setters are set_Property by convention // Setter is a special method and we don’t want it to appear to callers from C# MethodAttributes.PrivateScope | MethodAttributes.HideBySig | MethodAttributes.Public | MethodAttributes.SpecialName, typeof(void), // Setters don’t return a value new[] { typeof(int) }); // We have a single argument of type System.Int32
// To generate the body of the method, we’ll need an IL generator il = mbSetNumber.GetILGenerator(); il.Emit(OpCodes.Ldarg_0); // Load this il.Emit(OpCodes.Ldarg_1); // Load the new value il.Emit(OpCodes.Stfld, fbNumber); // Save the new value to this.m_number il.Emit(OpCodes.Ret); // Return
// Finally, link the method to the setter of our property pbNumber.SetSetMethod(mbSetNumber);
MethodBuilder mbGetNumber = tb.DefineMethod( “get_Number”, MethodAttributes.PrivateScope | MethodAttributes.HideBySig | MethodAttributes.Public | MethodAttributes.SpecialName, typeof(int), new Type[0]);
il = mbGetNumber.GetILGenerator(); il.Emit(OpCodes.Ldarg_0); // Load this il.Emit(OpCodes.Ldfld, fbNumber); // Load the value of this.m_number il.Emit(OpCodes.Ret); // Return the value
pbNumber.SetGetMethod(mbGetNumber); // Finally, we add the two constructors. // Constructor needs to call the constructor of the parent class, or another constructor in
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the same class ConstructorBuilder intConstructor = tb.DefineConstructor( MethodAttributes.Public, CallingConventions.Standard | CallingConventions.HasThis, new[] { typeof(int) }); il = intConstructor.GetILGenerator(); il.Emit(OpCodes.Ldarg_0); // this il.Emit(OpCodes.Call, typeof(object).GetConstructor(new Type[0])); // call parent’s constructor il.Emit(OpCodes.Ldarg_0); // this il.Emit(OpCodes.Ldarg_1); // our int argument il.Emit(OpCodes.Stfld, fbNumber); // store argument in this.m_number il.Emit(OpCodes.Ret);
var parameterlessConstructor = tb.DefineConstructor( MethodAttributes.Public, CallingConventions.Standard | CallingConventions.HasThis, new Type[0]); il = parameterlessConstructor.GetILGenerator(); il.Emit(OpCodes.Ldarg_0); // this il.Emit(OpCodes.Ldc_I4_S, (byte)42); // load 42 as an integer constant il.Emit(OpCodes.Call, intConstructor); // call this(42) il.Emit(OpCodes.Ret);
// And make sure the type is created Type ourType = tb.CreateType();
// The types from the assembly can be used directly using reflection, or we can save the assembly to use as a reference object ourInstance = Activator.CreateInstance(ourType); Console.WriteLine(ourType.GetProperty(“Number”).GetValue(ourInstance)); // 42 // Save the assembly for use elsewhere. This is very useful for debugging – you can use e.g. ILSpy to look at the equivalent IL/C# code. ab.Save(@”DynamicAssemblyExample.dll”); // Using newly created type var myDynamicType = tb.CreateType(); var myDynamicTypeInstance = Activator.CreateInstance(myDynamicType);
Console.WriteLine(myDynamicTypeInstance.GetType()); // MyDynamicType
var numberField = myDynamicType.GetField(“m_number”, BindingFlags.NonPublic | BindingFlags.Instance); numberField.SetValue (myDynamicTypeInstance, 10);
Console.WriteLine(numberField.GetValue(myDynamicTypeInstance)); // 10 } }
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Chapter 24: .NET Core
.NET Core is a general purpose development platform maintained by Microsoft and the .NET community on GitHub. It is cross-platform, supporting Windows, macOS and Linux, and can be used in device, cloud, and embedded/IoT scenarios.
When you think of .NET Core the following should come to mind (flexible deployment, cross-platform, command- line tools, open source).
Another great thing is that even if it’s open source Microsoft is actively supporting it.
Section 24.1: Basic Console App
public class Program { public static void Main(string[] args) { Console.WriteLine(“nWhat is your name? “); var name = Console.ReadLine(); var date = DateTime.Now; Console.WriteLine(“nHello, {0}, on {1:d} at {1:t}”, name, date); Console.Write(“nPress any key to exit…”); Console.ReadKey(true); } }
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Chapter 25: ADO.NET
ADO(ActiveX Data Objects).Net is a tool provided by Microsoft which provides access to data sources such as SQL Server, Oracle, and XML through its components. .Net front-end applications can retrieve, create, and manipulate data, once they are connected to a data source through ADO.Net with appropriate privileges.
ADO.Net provides a connection-less architecture. It is a secure approach to interact with a database, since, the connection doesn’t have to be maintained during the entire session.
Section 25.1: Best Practices – Executing Sql Statements
public void SaveNewEmployee(Employee newEmployee) { // best practice – wrap all database connections in a using block so they are always closed & disposed even in the event of an Exception // best practice – retrieve the connection string by name from the app.config or web.config (depending on the application type) (note, this requires an assembly reference to System.configuration) using(SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings[“MyConnectionName”].Conne ctionString)) { // best practice – use column names in your INSERT statement so you are not dependent on the sql schema column order // best practice – always use parameters to avoid sql injection attacks and errors if malformed text is used like including a single quote which is the sql equivalent of escaping or starting a string (varchar/nvarchar) // best practice – give your parameters meaningful names just like you do variables in your code using(SqlCommand sc = new SqlCommand(“INSERT INTO employee (FirstName, LastName, DateOfBirth /*etc*/) VALUES (@firstName, @lastName, @dateOfBirth /*etc*/)”, con)) { // best practice – always specify the database data type of the column you are using // best practice – check for valid values in your code and/or use a database constraint, if inserting NULL then use System.DbNull.Value sc.Parameters.Add(new SqlParameter(“@firstName”, SqlDbType.VarChar, 200){Value = newEmployee.FirstName ?? (object) System.DBNull.Value}); sc.Parameters.Add(new SqlParameter(“@lastName”, SqlDbType.VarChar, 200){Value = newEmployee.LastName ?? (object) System.DBNull.Value});
// best practice – always use the correct types when specifying your parameters, Value is assigned to a DateTime instance and not a string representation of a Date sc.Parameters.Add(new SqlParameter(“@dateOfBirth”, SqlDbType.Date){ Value = newEmployee.DateOfBirth });
// best practice – open your connection as late as possible unless you need to verify that the database connection is valid and won’t fail and the proceeding code execution takes a long time (not the case here) con.Open(); sc.ExecuteNonQuery(); }
// the end of the using block will close and dispose the SqlConnection // best practice – end the using block as soon as possible to release the database connection } }
// supporting class used as parameter for example public class Employee
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{ public string FirstName { get; set; } public string LastName { get; set; } public DateTime DateOfBirth { get; set; } }
Best practice for working with ADO.NET
Rule of thumb is to open connection for minimal time. Close the connection explicitly once your procedure execution is over this will return the connection object back to connection pool. Default connection pool max size = 100. As connection pooling enhances the performance of physical connection to SQL Server.Connection Pooling in SQL Server Wrap all database connections in a using block so they are always closed & disposed even in the event of an Exception. See using Statement (C# Reference) for more information on using statements Retrieve the connection strings by name from the app.config or web.config (depending on the application type)
This requires an assembly reference to System.configuration See Connection Strings and Configuration Files for additional information on how to structure your configuration file
Always use parameters for incoming values to
Avoid sql injection attacks Avoid errors if malformed text is used like including a single quote which is the sql equivalent of escaping or starting a string (varchar/nvarchar) Letting the database provider reuse query plans (not supported by all database providers) which increases efficiency
When working with parameters
Sql parameters type and size mismatch is a common cause of insert/ updated/ select failure Give your Sql parameters meaningful names just like you do variables in your code Specify the database data type of the column you are using, this ensures the wrong parameter types is not used which could lead to unexpected results Validate your incoming parameters before you pass them into the command (as the saying goes, “garbage in, garbage out”). Validate incoming values as early as possible in the stack Use the correct types when assigning your parameter values, example: do not assign the string value of a DateTime, instead assign an actual DateTime instance to the value of the parameter Specify the size of string-type parameters. This is because SQL Server can re-use execution plans if the parameters match in type and size. Use -1 for MAX Do not use the method AddWithValue, the main reason is it is very easy to forget to specify the parameter type or the precision/scale when needed. For additional information see Can we stop using AddWithValue already?
When using database connections
Open the connection as late as possible and close it as soon as possible. This is a general guideline when working with any external resource Never share database connection instances (example: having a singleton host a shared instance of type SqlConnection). Have your code always create a new database connection instance when needed and then have the calling code dispose of it and “throw it away” when it is done. The reason for this is
Most database providers have some sort of connection pooling so creating new managed connections is cheap It eliminates any future errors if the code starts working with multiple threads
Section 25.2: Executing SQL statements as a command
// Uses Windows authentication. Replace the Trusted_Connection parameter with
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// User Id=…;Password=…; to use SQL Server authentication instead. You may // want to find the appropriate connection string for your server. string connectionString = @”Server=myServermyInstance;Database=myDataBase;Trusted_Connection=True;”
string sql = “INSERT INTO myTable (myDateTimeField, myIntField) ” + “VALUES (@someDateTime, @someInt);”;
// Most ADO.NET objects are disposable and, thus, require the using keyword. using (var connection = new SqlConnection(connectionString)) using (var command = new SqlCommand(sql, connection)) { // Use parameters instead of string concatenation to add user-supplied // values to avoid SQL injection and formatting issues. Explicitly supply datatype.
// System.Data.SqlDbType is an enumeration. See Note1 command.Parameters.Add(“@someDateTime”, SqlDbType.DateTime).Value = myDateTimeVariable; command.Parameters.Add(“@someInt”, SqlDbType.Int).Value = myInt32Variable;
// Execute the SQL statement. Use ExecuteScalar and ExecuteReader instead // for query that return results (or see the more specific examples, once // those have been added).
connection.Open(); command.ExecuteNonQuery(); }
Note 1: Please see SqlDbType Enumeration for the MSFT SQL Server-specific variation.
Note 2: Please see MySqlDbType Enumeration for the MySQL-specific variation. Section 25.3: Using common interfaces to abstract away vendor specific classes
var providerName = “System.Data.SqlClient”; //Oracle.ManagedDataAccess.Client, IBM.Data.DB2 var connectionString = “{your-connection-string}”; //you will probably get the above two values in the ConnectionStringSettings object from .config file
var factory = DbProviderFactories.GetFactory(providerName); using(var connection = factory.CreateConnection()) { //IDbConnection connection.ConnectionString = connectionString; connection.Open(); using(var command = connection.CreateCommand()) { //IDbCommand command.CommandText = “{query}”; using(var reader = command.ExecuteReader()) { //IDataReader while(reader.Read()) { … } } } }
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Chapter 26: Dependency Injection Section 26.1: How Dependency Injection Makes Unit Testing Easier
This builds on the previous example of the Greeter class which has two dependencies, IGreetingProvider and IGreetingWriter.
The actual implementation of IGreetingProvider might retrieve a string from an API call or a database. The implementation of IGreetingWriter might display the greeting in the console. But because Greeter has its dependencies injected into its constructor, it’s easy to write a unit test that injects mocked versions of those interfaces. In real life we might use a framework like Moq, but in this case I’ll write those mocked implementations.
public class TestGreetingProvider : IGreetingProvider { public const string TestGreeting = “Hello!”;
public string GetGreeting() { return TestGreeting; } }
public class TestGreetingWriter : List, IGreetingWriter { public void WriteGreeting(string greeting) { Add(greeting); } }
[TestClass] public class GreeterTests { [TestMethod] public void Greeter_WritesGreeting() { var greetingProvider = new TestGreetingProvider(); var greetingWriter = new TestGreetingWriter(); var greeter = new Greeter(greetingProvider, greetingWriter); greeter.Greet(); Assert.AreEqual(greetingWriter[0], TestGreetingProvider.TestGreeting); } }
The behavior of IGreetingProvider and IGreetingWriter are not relevant to this test. We want to test that Greeter gets a greeting and writes it. The design of Greeter (using dependency injection) allows us to inject mocked dependencies without any complicated moving parts. All we’re testing is that Greeter interacts with those dependencies as we expect it to.
Section 26.2: Dependency Injection – Simple example
This class is called Greeter. Its responsibility is to output a greeting. It has two dependencies. It needs something that will give it the greeting to output, and then it needs a way to output that greeting. Those dependencies are both described as interfaces, IGreetingProvider and IGreetingWriter. In this example, those two dependencies are “injected” into Greeter. (Further explanation following the example.)
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public class Greeter { private readonly IGreetingProvider _greetingProvider; private readonly IGreetingWriter _greetingWriter;
public Greeter(IGreetingProvider greetingProvider, IGreetingWriter greetingWriter) { _greetingProvider = greetingProvider; _greetingWriter = greetingWriter; }
public void Greet() { var greeting = _greetingProvider.GetGreeting(); _greetingWriter.WriteGreeting(greeting); } }
public interface IGreetingProvider { string GetGreeting(); }
public interface IGreetingWriter { void WriteGreeting(string greeting); }
The Greeting class depends on both IGreetingProvider and IGreetingWriter, but it is not responsible for creating instances of either. Instead it requires them in its constructor. Whatever creates an instance of Greeting must provide those two dependencies. We can call that “injecting” the dependencies.
Because dependencies are provided to the class in its constructor, this is also called “constructor injection.”
A few common conventions:
The constructor saves the dependencies as private fields. As soon as the class is instantiated, those dependencies are available to all other non-static methods of the class. The private fields are readonly. Once they are set in the constructor they cannot be changed. This indicates that those fields should not (and cannot) be modified outside of the constructor. That further ensures that those dependencies will be available for the lifetime of the class. The dependencies are interfaces. This is not strictly necessary, but is common because it makes it easier to substitute one implementation of the dependency with another. It also allows providing a mocked version of the interface for unit testing purposes.
Section 26.3: Why We Use Dependency Injection Containers (IoC Containers)
Dependency injection means writing classes so that they do not control their dependencies – instead, their dependencies are provided to them (“injected.”)
This is not the same thing as using a dependency injection framework (often called a “DI container”, “IoC container”, or just “container”) like Castle Windsor, Autofac, SimpleInjector, Ninject, Unity, or others.
A container just makes dependency injection easier. For example, suppose you write a number of classes that rely on dependency injection. One class depends on several interfaces, the classes that implement those interfaces depend on other interfaces, and so on. Some depend on specific values. And just for fun, some of those classes
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implement IDisposable and need to be disposed.
Each individual class is well-written and easy to test. But now there’s a different problem: Creating an instance of a class has become much more complicated. Suppose we’re creating an instance of a CustomerService class. It has dependencies and its dependencies have dependencies. Constructing an instance might look something like this:
public CustomerData GetCustomerData(string customerNumber) { var customerApiEndpoint = ConfigurationManager.AppSettings[“customerApi:customerApiEndpoint”]; var logFilePath = ConfigurationManager.AppSettings[“logwriter:logFilePath”]; var authConnectionString = ConfigurationManager.ConnectionStrings[“authorization”].ConnectionString; using(var logWriter = new LogWriter(logFilePath )) { using(var customerApiClient = new CustomerApiClient(customerApiEndpoint)) { var customerService = new CustomerService( new SqlAuthorizationRepository(authorizationConnectionString, logWriter), new CustomerDataRepository(customerApiClient, logWriter), logWriter ); // All this just to create an instance of CustomerService! return customerService.GetCustomerData(string customerNumber); } } }
You might wonder, why not put the whole giant construction in a separate function that just returns CustomerService? One reason is that because the dependencies for each class are injected into it, a class isn’t responsible for knowing whether those dependencies are IDisposable or disposing them. It just uses them. So if a we had a GetCustomerService() function that returned a fully-constructed CustomerService, that class might contain a number of disposable resources and no way to access or dispose them.
And aside from disposing IDisposable, who wants to call a series of nested constructors like that, ever? That’s a short example. It could get much, much worse. Again, that doesn’t mean that we wrote the classes the wrong way. The classes might be individually perfect. The challenge is composing them together.
A dependency injection container simplifies that. It allows us to specify which class or value should be used to fulfill each dependency. This slightly oversimplified example uses Castle Windsor:
var container = new WindsorContainer() container.Register( Component.For(), Component.For() .DependsOn(Dependency.OnAppSettingsValue(“logFilePath”, “logWriter:logFilePath”)), Component.For() .DependsOn(Dependency.OnValue(connectionString, ConfigurationManager.ConnectionStrings[“authorization”].ConnectionString)), Component.For() .DependsOn(Dependency.OnAppSettingsValue(“apiEndpoint”, “customerApi:customerApiEndpoint”)) );
We call this “registering dependencies” or “configuring the container.” Translated, this tells our WindsorContainer:
If a class requires ILogWriter, create an instance of LogWriter. LogWriter requires a file path. Use this value from AppSettings.
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If a class requires IAuthorizationRepository, create an instance of SqlAuthorizationRepository. It requires a connection string. Use this value from the ConnectionStrings section. If a class requires ICustomerDataProvider, create a CustomerApiClient and provide the string it needs from AppSettings.
When we request a dependency from the container we call that “resolving” a dependency. It’s bad practice to do that directly using the container, but that’s a different story. For demonstration purposes, we could now do this:
var customerService = container.Resolve(); var data = customerService.GetCustomerData(customerNumber); container.Release(customerService);
The container knows that CustomerService depends on IAuthorizationRepository and ICustomerDataProvider. It knows what classes it needs to create to fulfill those requirements. Those classes, in turn, have more dependencies, and the container knows how to fulfill those. It will create every class it needs to until it can return an instance of CustomerService.
If it gets to a point where a class requires a dependency that we haven’t registered, like IDoesSomethingElse, then when we try to resolve CustomerService it will throw a clear exception telling us that we haven’t registered anything to fulfill that requirement.
Each DI framework behaves a little differently, but typically they give us some control over how certain classes are instantiated. For example, do we want it to create one instance of LogWriter and provide it to every class that depends on ILogWriter, or do we want it to create a new one every time? Most containers have a way to specify that.
What about classes that implement IDisposable? That’s why we call container.Release(customerService); at the end. Most containers (including Windsor) will step back through all of the dependencies created and Dispose the ones that need disposing. If CustomerService is IDisposable it will dispose that too.
Registering dependencies as seen above might just look like more code to write. But when we have lots of classes with lots of dependencies then it really pays off. And if we had to write those same classes without using dependency injection then that same application with lots of classes would become difficult to maintain and test.
This scratches the surface of why we use dependency injection containers. How we configure our application to use one (and use it correctly) is not just one topic – it’s a number of topics, as the instructions and examples vary from one container to the next.
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Chapter 27: Platform Invoke Section 27.1: Marshaling structs Simple struct
C++ signature:
typedef struct _PERSON { int age; char name[32]; } PERSON, *LP_PERSON;
void GetSpouse(PERSON person, LP_PERSON spouse);
C# definition
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public struct PERSON { public int age; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)] public string name; }
[DllImport(“family.dll”, CharSet = CharSet.Auto)] public static extern bool GetSpouse(PERSON person, ref PERSON spouse);
Struct with unknown size array fields. Passing in
C++ signature
typedef struct { int length; int *data; } VECTOR;
void SetVector(VECTOR &vector);
When passed from managed to unmanaged code, this
The data array should be defined as IntPtr and memory should be explicitly allocated with Marshal.AllocHGlobal() (and freed with Marshal.FreeHGlobal() afterwords):
[StructLayout(LayoutKind.Sequential)] public struct VECTOR : IDisposable { int length; IntPtr dataBuf;
public int[] data { set { FreeDataBuf();
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if (value != null && value.Length > 0) { dataBuf = Marshal.AllocHGlobal(value.Length * Marshal.SizeOf(value[0])); Marshal.Copy(value, 0, dataBuf, value.Length); length = value.Length; } } } void FreeDataBuf() { if (dataBuf != IntPtr.Zero) { Marshal.FreeHGlobal(dataBuf); dataBuf = IntPtr.Zero; } } public void Dispose() { FreeDataBuf(); } }
[DllImport(“vectors.dll”)] public static extern void SetVector([In]ref VECTOR vector);
Struct with unknown size array fields. Receiving
C++ signature:
typedef struct { char *name; } USER;
bool GetCurrentUser(USER *user);
When such data is passed out of unmanaged code and memory is allocated by the unmanaged functions, the managed caller should receive it into an IntPrt variable and convert the buffer to a managed array. In case of strings there is a convenient Marshal.PtrToStringAnsi() method:
[StructLayout(LayoutKind.Sequential)] public struct USER { IntPtr nameBuffer; public string name { get { return Marshal.PtrToStringAnsi(nameBuffer); } } }
[DllImport(“users.dll”)] public static extern bool GetCurrentUser(out USER user);
Section 27.2: Marshaling unions Value-type fields only
C++ declaration
typedef union { char c;
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int i; } CharOrInt;
C# declaration
[StructLayout(LayoutKind.Explicit)] public struct CharOrInt { [FieldOffset(0)] public byte c; [FieldOffset(0)] public int i; }
Mixing value-type and reference fields
Overlapping a reference value with a value type one is not allowed so you cannot simply use the FieldOffset(0) text; FieldOffset(0) i; will not compile for
typedef union { char text[128]; int i; } TextOrInt;
and generally you would have to employ custom marshaling. However, in particular cases like this simpler technics may be used:
[StructLayout(LayoutKind.Sequential)] public struct TextOrInt { [MarshalAs(UnmanagedType.ByValArray, SizeConst = 128)] public byte[] text; public int i { get { return BitConverter.ToInt32(text, 0); } } }
Section 27.3: Calling a Win32 dll function
using System.Runtime.InteropServices;
class PInvokeExample { [DllImport(“user32.dll”, CharSet = CharSet.Auto)] public static extern uint MessageBox(IntPtr hWnd, String text, String caption, int options);
public static void test() { MessageBox(IntPtr.Zero, “Hello!”, “Message”, 0); } }
Declare a function as static extern stting DllImportAttribute with its Value property set to .dll name. Don’t forget to use System.Runtime.InteropServices namespace. Then call it as an regular static method.
The Platform Invocation Services will take care of loading the .dll and finding the desired finction. The P/Invoke in most simple cases will also marshal parameters and return value to and from the .dll (i.e. convert from .NET datatypes to Win32 ones and vice versa).
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Section 27.4: Using Windows API
Use pinvoke.net.
Before declaring an extern Windows API function in your code, consider looking for it on pinvoke.net. They most likely already have a suitable declaration with all supporting types and good examples.
Section 27.5: Marshalling arrays Arrays of simple type
[DllImport(“Example.dll”)] static extern void SetArray( [MarshalAs(UnmanagedType.LPArray, SizeConst = 128)] byte[] data);
Arrays of string
[DllImport(“Example.dll”)] static extern void SetStrArray(string[] textLines);
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Chapter 28: NuGet packaging system Section 28.1: Uninstalling a package from one project in a solution
PM> Uninstall-Package -ProjectName MyProjectB EntityFramework
Section 28.2: Installing a specific version of a package
PM> Install-Package EntityFramework -Version 6.1.2
Section 28.3: Adding a package source feed (MyGet, Klondike, ect)
nuget sources add -name feedname -source http://sourcefeedurl
Section 28.4: Installing the NuGet Package Manager
In order to be able to manage your projects’ packages, you need the NuGet Package Manager. This is a Visual Studio Extension, explained in the official docs: Installing and Updating NuGet Client.
Starting with Visual Studio 2012, NuGet is included in every edition, and can be used from: Tools -> NuGet Package Manager -> Package Manager Console.
You do so through the Tools menu of Visual Studio, clicking Extensions and Updates:
This installs both the GUI:
Available through clicking “Manage NuGet Packages…” on a project or its References folder
And the Package Manager Console:
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Tools -> NuGet Package Manager -> Package Manager Console.
Section 28.5: Managing Packages through the UI
When you right-click a project (or its References folder), you can click the “Manage NuGet Packages…” option. This shows the Package Manager Dialog.
Section 28.6: Managing Packages through the console
Click the menus Tools -> NuGet Package Manager -> Package Manager Console to show the console in your IDE. Official documentation here.
Here you can issue, amongst others, install-package commands which installs the entered package into the currently selected “Default project”:
Install-Package Elmah
You can also provide the project to install the package to, overriding the selected project in the “Default project” dropdown:
Install-Package Elmah -ProjectName MyFirstWebsite
Section 28.7: Updating a package
To update a package use the following command:
PM> Update-Package EntityFramework
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where EntityFramework is the name of the package to be updated. Note that update will run for all projects, and so is different from Install-Package EntityFramework which would install to “Default project” only.
You can also specify a single project explicitly:
PM> Update-Package EntityFramework -ProjectName MyFirstWebsite
Section 28.8: Uninstalling a package
PM> Uninstall-Package EntityFramework
Section 28.9: Uninstall a specific version of package
PM> uninstall-Package EntityFramework -Version 6.1.2
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Chapter 29: Globalization in ASP.NET MVC using Smart internationalization for ASP.NET Section 29.1: Basic configuration and setup
1. 2.
Add the I18N nuget package to your MVC project. In web.config, add the i18n.LocalizingModule to your or section.


3.
4. 5.
Add a folder named “locale” to the root of your site. Create a subfolder for each culture you wish to support. For example, /locale/fr/. In each culture-specific folder, create a text file named messages.po. For testing purposes, enter the following lines of text in your messages.po file:
#: Translation test msgid “Hello, world!” msgstr “Bonjour le monde!”
6.
Add a controller to your project which returns some text to translate.
using System.Web.Mvc;
namespace I18nDemo.Controllers { public class DefaultController : Controller { public ActionResult Index() { // Text inside [[[triple brackets]]] must precisely match // the msgid in your .po file. return Content(“[[[Hello, world!]]]”); } } }
7.
8.
9.
Run your MVC application and browse to the route corresponding to your controller action, such as http://localhost:[yourportnumber]/default. Observe that the URL is changed to reflect your default culture, such as http://localhost:[yourportnumber]/en/default. Replace /en/ in the URL with /fr/ (or whatever culture you’ve selected.) The page should now display the translated version of your text. Change your browser’s language setting to prefer your alternate culture and browse to /default again. Observe that the URL is changed to reflect your alternate culture and the translated text appears.
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10.
In web.config, add handlers so that users cannot browse to your locale folder.


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Chapter 30: System.Net.Mail Section 30.1: MailMessage
Here is the example of creating of mail message with attachments. After creating we send this message with the help of SmtpClient class. Default 25 port is used here.
public class clsMail { private static bool SendMail(string mailfrom, Listreplytos, List mailtos, List mailccs, List mailbccs, string body, string subject, List Attachment) { try { using(MailMessage MyMail = new MailMessage()) { MyMail.From = new MailAddress(mailfrom); foreach (string mailto in mailtos) MyMail.To.Add(mailto);
if (replytos != null && replytos.Any()) { foreach (string replyto in replytos) MyMail.ReplyToList.Add(replyto); }
if (mailccs != null && mailccs.Any()) { foreach (string mailcc in mailccs) MyMail.CC.Add(mailcc); }
if (mailbccs != null && mailbccs.Any()) { foreach (string mailbcc in mailbccs) MyMail.Bcc.Add(mailbcc); }
MyMail.Subject = subject; MyMail.IsBodyHtml = true; MyMail.Body = body; MyMail.Priority = MailPriority.Normal;
if (Attachment != null && Attachment.Any()) { System.Net.Mail.Attachment attachment; foreach (var item in Attachment) { attachment = new System.Net.Mail.Attachment(item); MyMail.Attachments.Add(attachment); } }
SmtpClient smtpMailObj = new SmtpClient(); smtpMailObj.Host = “your host”; smtpMailObj.Port = 25; smtpMailObj.Credentials = new System.Net.NetworkCredential(“uid”, “pwd”);
smtpMailObj.Send(MyMail); return true;
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} } catch { return false; } } }
Section 30.2: Mail with Attachment
MailMessage represents mail message which can be sent further using SmtpClient class. Several attachments (files) can be added to mail message.
using System.Net.Mail;
using(MailMessage myMail = new MailMessage()) { Attachment attachment = new Attachment(path); myMail.Attachments.Add(attachment);
// further processing to send the mail message
}
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Chapter 31: Using Progress and IProgress Section 31.1: Simple Progress reporting
IProgress can be used to report progress of some procedure to another procedure. This example shows how you can create a basic method that reports its progress.
void Main() { IProgress p = new Progress(progress => { Console.WriteLine(“Running Step: {0}”, progress); }); LongJob(p); }
public void LongJob(IProgress progress) { var max = 10; for (int i = 0; i < max; i++) { progress.Report(i); } }
Output:
Running Step: 0 Running Step: 3 Running Step: 4 Running Step: 5 Running Step: 6 Running Step: 7 Running Step: 8 Running Step: 9 Running Step: 2 Running Step: 1
Note that when you this code runs, you may see numbers be output out of order. This is because the IProgress.Report() method is run asynchronously, and is therefore not as suitable for situations where the progress must be reported in order.
Section 31.2: Using IProgress
It’s important to note that the System.Progress class does not have the Report() method available on it. This method was implemented explicitly from the IProgress interface, and therefore must be called on a Progress when it’s cast to an IProgress.
var p1 = new Progress(); p1.Report(1); //compiler error, Progress does not contain method ‘Report’
IProgress p2 = new Progress(); p2.Report(2); //works
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var p3 = new Progress(); ((IProgress)p3).Report(3); //works
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Chapter 32: JSON Serialization Section 32.1: Deserialization using System.Web.Script.Serialization.JavaScriptSerializer
The JavaScriptSerializer.Deserialize(input) method attempts to deserialize a string of valid JSON into an object of the specified type , using the default mappings natively supported by JavaScriptSerializer.
using System.Collections; using System.Web.Script.Serialization;
// …
string rawJSON = “{“Name”:”Fibonacci Sequence”,”Numbers”:[0, 1, 1, 2, 3, 5, 8, 13]}”;
JavaScriptSerializer JSS = new JavaScriptSerializer(); Dictionary parsedObj = JSS.Deserialize<Dictionary>(rawJSON);
string name = parsedObj[“Name”].toString(); ArrayList numbers = (ArrayList)parsedObj[“Numbers”]
Note: The JavaScriptSerializer object was introduced in .NET version 3.5
Section 32.2: Serialization using Json.NET
[JsonObject(“person”)] public class Person { [JsonProperty(“name”)] public string PersonName { get; set; } [JsonProperty(“age”)] public int PersonAge { get; set; } [JsonIgnore] public string Address { get; set; } }
Person person = new Person { PersonName = “Andrius”, PersonAge = 99, Address = “Some address” }; string rawJson = JsonConvert.SerializeObject(person);
Console.WriteLine(rawJson); // {“name”:”Andrius”,”age”:99}
Notice how properties (and classes) can be decorated with attributes to change their appearance in resulting json string or to remove them from json string at all (JsonIgnore).
More information about Json.NET serialization attributes can be found here.
In C#, public identifiers are written in PascalCase by convention. In JSON, the convention is to use camelCase for all names. You can use a contract resolver to convert between the two.
using Newtonsoft.Json; using Newtonsoft.Json.Serialization;
public class Person { public string Name { get; set; } public int Age { get; set; } [JsonIgnore]
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public string Address { get; set; } }
public void ToJson() { Person person = new Person { Name = “Andrius”, Age = 99, Address = “Some address” }; var resolver = new CamelCasePropertyNamesContractResolver(); var settings = new JsonSerializerSettings { ContractResolver = resolver }; string json = JsonConvert.SerializeObject(person, settings);
Console.WriteLine(json); // {“name”:”Andrius”,”age”:99} }
Section 32.3: Serialization-Deserialization using Newtonsoft.Json
Unlike the other helpers, this one uses static class helpers to serialize and deserialize, hence it is a little bit easier than the others to use.
using Newtonsoft.Json;
var rawJSON = “{“Name”:”Fibonacci Sequence”,”Numbers”:[0, 1, 1, 2, 3, 5, 8, 13]}”; var fibo = JsonConvert.DeserializeObject<Dictionary>(rawJSON); var rawJSON2 = JsonConvert.SerializeObject(fibo);
Section 32.4: Deserialization using Json.NET
internal class Sequence{ public string Name; public List Numbers; }
// …
string rawJSON = “{“Name”:”Fibonacci Sequence”,”Numbers”:[0, 1, 1, 2, 3, 5, 8, 13]}”;
Sequence sequence = JsonConvert.DeserializeObject(rawJSON);
For more information, refer to the Json.NET official site.
Note: Json.NET supports .NET version 2 and higher.
Section 32.5: Dynamic binding
Newtonsoft’s Json.NET allows you to bind json dynamically (using ExpandoObject / Dynamic objects) without the need to create the type explicitly.
Serialization
dynamic jsonObject = new ExpandoObject(); jsonObject.Title = “Merchent of Venice”; jsonObject.Author = “William Shakespeare”; Console.WriteLine(JsonConvert.SerializeObject(jsonObject));
De-serialization
var rawJson = “{“Name”:”Fibonacci Sequence”,”Numbers”:[0, 1, 1, 2, 3, 5, 8, 13]}”; dynamic parsedJson = JObject.Parse(rawJson);
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Console.WriteLine(“Name: ” + parsedJson.Name); Console.WriteLine(“Name: ” + parsedJson.Numbers.Length);
Notice that the keys in the rawJson object have been turned into member variables in the dynamic object.
This is useful in cases where an application can accept/ produce varying formats of JSON. It is however suggested to use an extra level of validation for the Json string or to the dynamic object generated as a result of serialization/ de- serialization.
Section 32.6: Serialization using Json.NET with JsonSerializerSettings
This serializer has some nice features that the default .net json serializer doesn’t have, like Null value handling, you just need to create the JsonSerializerSettings :
public static string Serialize(T obj) { string result = JsonConvert.SerializeObject(obj, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore}); return result; }
Another serious serializer issue in .net is the self referencing loop. In the case of a student that is enrolled in a course, its instance has a course property and a course has a collection of students that means a List which will create a reference loop. You can handle this with JsonSerializerSettings :
public static string Serialize(T obj) { string result = JsonConvert.SerializeObject(obj, new JsonSerializerSettings { ReferenceLoopHandling = ReferenceLoopHandling.Ignore}); return result; }
You can put various serializations option like this:
public static string Serialize(T obj) { string result = JsonConvert.SerializeObject(obj, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore, ReferenceLoopHandling = ReferenceLoopHandling.Ignore}); return result; }
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Chapter 33: JSON in .NET with Newtonsoft.Json
The NuGet package Newtonsoft.Json has become the defacto standard for using and manipulating JSON formatted text and objects in .NET. It is a robust tool that is fast, and easy to use.
Section 33.1: Deserialize an object from JSON text
var json = “{“Name”:”Joe Smith”,”Age”:21}”; var person = JsonConvert.DeserializeObject(json);
This yields a Person object with Name “Joe Smith” and Age 21.
Section 33.2: Serialize object into JSON
using Newtonsoft.Json;
var obj = new Person { Name = “Joe Smith”, Age = 21 }; var serializedJson = JsonConvert.SerializeObject(obj);
This results in this JSON: {“Name”:”Joe Smith”,”Age”:21}
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Chapter 34: XmlSerializer Section 34.1: Formatting: Custom DateTime format
public class Dog { private const string _birthStringFormat = “yyyy-MM-dd”;
[XmlIgnore] public DateTime Birth {get; set;}
[XmlElement(ElementName=”Birth”)] public string BirthString { get { return Birth.ToString(_birthStringFormat); } set { Birth = DateTime.ParseExact(value, _birthStringFormat, CultureInfo.InvariantCulture); } } }
Section 34.2: Serialize object
public void SerializeFoo(string fileName, Foo foo) { var serializer = new XmlSerializer(typeof(Foo)); using (var stream = File.Open(fileName, FileMode.Create)) { serializer.Serialize(stream, foo); } }
Section 34.3: Deserialize object
public Foo DeserializeFoo(string fileName) { var serializer = new XmlSerializer(typeof(Foo)); using (var stream = File.OpenRead(fileName)) { return (Foo)serializer.Deserialize(stream); } }
Section 34.4: Behaviour: Map array name to property (XmlArray)

public class Store { [XmlArray(“Articles”)]
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public List Products {get; set; } }
Section 34.5: Behaviour: Map Element name to Property

public class Foo { // Using XmlElement [XmlElement(Name=”Dog”)] public Animal Cat { get; set; } }
Section 34.6: Eciently building multiple serializers with derived types specified dynamically Where we came from
Sometimes we can’t provide all of the required metadata needed for the XmlSerializer framework in attribute. Suppose we have a base class of serialized objects, and some of the derived classes are unknown to the base class. We can’t place an attribute for all of the classes which are not know at the design time of the base type. We could have another team developing some of the derived classes.
What can we do
We can use new XmlSerializer(type, knownTypes), but that would be a O(N^2) operation for N serializers, at least to discover all of the types supplied in arguments:
// Beware of the N^2 in terms of the number of types. var allSerializers = allTypes.Select(t => new XmlSerializer(t, allTypes)); var serializerDictionary = Enumerable.Range(0, allTypes.Length) .ToDictionary (i => allTypes[i], i => allSerializers[i])
In this example, the the Base type is not aware of it’s derived types, which is normal in OOP.
Doing it efficiently
Luckily, there is a method which addresses this particular problem – supplying known types for multiple serializers efficiently:
System.Xml.Serialization.XmlSerializer.FromTypes Method (Type[])
The FromTypes method allows you to efficiently create an array of XmlSerializer objects for processing an array of Type objects.
var allSerializers = XmlSerializer.FromTypes(allTypes); var serializerDictionary = Enumerable.Range(0, allTypes.Length) .ToDictionary(i => allTypes[i], i => allSerializers[i]);
Here is a complete code sample:
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using System; using System.Collections.Generic; using System.Xml.Serialization; using System.Linq; using System.Linq; public class Program { public class Container { public Base Base { get; set; } } public class Base { public int JustSomePropInBase { get; set; } } public class Derived : Base { public int JustSomePropInDerived { get; set; } } public void Main() { var sampleObject = new Container { Base = new Derived() }; var allTypes = new[] { typeof(Container), typeof(Base), typeof(Derived) }; Console.WriteLine(“Trying to serialize without a derived class metadata:”); SetupSerializers(allTypes.Except(new[] { typeof(Derived) }).ToArray()); try { Serialize(sampleObject); } catch (InvalidOperationException e) { Console.WriteLine(); Console.WriteLine(“This error was anticipated,”); Console.WriteLine(“we have not supplied a derived class.”); Console.WriteLine(e); } Console.WriteLine(“Now trying to serialize with all of the type information:”); SetupSerializers(allTypes); Serialize(sampleObject); Console.WriteLine(); Console.WriteLine(“Slides down well this time!”); }
static void Serialize(T o) { serializerDictionary[typeof(T)].Serialize(Console.Out, o); }
private static Dictionary serializerDictionary; static void SetupSerializers(Type[] allTypes) { var allSerializers = XmlSerializer.FromTypes(allTypes); serializerDictionary = Enumerable.Range(0, allTypes.Length) .ToDictionary(i => allTypes[i], i => allSerializers[i]); }
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}
Output:
Trying to serialize without a derived class metadata: System.InvalidOperationException: The type Program+Derived was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically. at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write2_Base(String n, String ns, Base o, Boolean isNullable, Boolean needType) at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write3_Container(String n, String ns, Container o, Boolean isNullable, Boolean needType) at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write4_Container(Object o) at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id) — End of inner exception stack trace — at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id) at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle) at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces) at Program.Serialize[T](T o) at Program.Main() Now trying to serialize with all of the type information:
0 0
Slides down well this time!
What’s in the output
This error message recommends what we tried to avoid (or what we can not do in some scenarios) – referencing derived types from base class:
Use the XmlInclude or SoapInclude attribute to specify types that are not known statically.
This is how we get our derived class in the XML:

Base corresponds to the property type declared in the Container type, and Derived being the type of the instance actually supplied.
Here is a working example fiddle
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Chapter 35: VB Forms Section 35.1: Hello World in VB.NET Forms
To show a message box when the form has been shown:
Public Class Form1 Private Sub Form1_Shown(sender As Object, e As EventArgs) Handles MyBase.Shown MessageBox.Show(“Hello, World!”) End Sub End Class To show a message box before the form has been shown:
Public Class Form1 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load MessageBox.Show(“Hello, World!”) End Sub End Class
Load() will be called first, and only once, when the form first loads. Show() will be called every time the user launches the form. Activate() will be called every time the user makes the form active.
Load() will execute before Show() is called, but be warned: calling msgBox() in show can cause that msgBox() to execute before Load() is finished. It is generally a bad idea to depend on event ordering between Load(), Show(), and similar. Section 35.2: For Beginners
Some things all beginners should know / do that will help them have a good start with VB .Net:
Set the following Options:
‘can be permanently set ‘ Tools / Options / Projects and Soluntions / VB Defaults Option Strict On Option Explicit On Option Infer Off
Public Class Form1
End Class
Use &, not + for string concatenation. Strings should be studied in some detail as they are widely used.
Spend some time understanding Value and Reference Types.
Never use Application.DoEvents. Pay attention to the ‘Caution’. When you reach a point where this seems like something you must use, ask.
The documentation is your friend.
Section 35.3: Forms Timer The Windows.Forms.Timer component can be used to provide the user information that is not time critical. Create a form with one button, one label, and a Timer component.
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For example it could be used to show the user the time of day periodically.
‘can be permanently set ‘ Tools / Options / Projects and Soluntions / VB Defaults Option Strict On Option Explicit On Option Infer Off
Public Class Form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Button1.Enabled = False Timer1.Interval = 60 * 1000 ‘one minute intervals ‘start timer Timer1.Start() Label1.Text = DateTime.Now.ToLongTimeString End Sub
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick Label1.Text = DateTime.Now.ToLongTimeString End Sub End Class
But this timer is not suited for timing. An example would be using it for a countdown. In this example we will simulate a countdown to three minutes. This may very well be one of the most boringly important examples here.
‘can be permanently set ‘ Tools / Options / Projects and Soluntions / VB Defaults Option Strict On Option Explicit On Option Infer Off
Public Class Form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Button1.Enabled = False ctSecs = 0 ‘clear count Timer1.Interval = 1000 ‘one second in ms. ‘start timers stpw.Reset() stpw.Start() Timer1.Start() End Sub
Dim stpw As New Stopwatch Dim ctSecs As Integer
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick ctSecs += 1 If ctSecs = 180 Then ‘about 2.5 seconds off on my PC! ‘stop timing stpw.Stop() Timer1.Stop() ‘show actual elapsed time ‘Is it near 180? Label1.Text = stpw.Elapsed.TotalSeconds.ToString(“n1”) End If End Sub End Class
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After button1 is clicked, about three minutes pass and label1 shows the results. Does label1 show 180? Probably not. On my machine it showed 182.5!
The reason for the discrepancy is in the documentation, “The Windows Forms Timer component is single-threaded, and is limited to an accuracy of 55 milliseconds.” This is why it shouldn’t be used for timing.
By using the timer and stopwatch a little differently we can obtain better results.
‘can be permanently set ‘ Tools / Options / Projects and Soluntions / VB Defaults Option Strict On Option Explicit On Option Infer Off
Public Class Form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Button1.Enabled = False Timer1.Interval = 100 ‘one tenth of a second in ms. ‘start timers stpw.Reset() stpw.Start() Timer1.Start() End Sub
Dim stpw As New Stopwatch Dim threeMinutes As TimeSpan = TimeSpan.FromMinutes(3)
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick If stpw.Elapsed >= threeMinutes Then ‘0.1 off on my PC! ‘stop timing stpw.Stop() Timer1.Stop() ‘show actual elapsed time ‘how close? Label1.Text = stpw.Elapsed.TotalSeconds.ToString(“n1”) End If End Sub End Class
There are other timers that can be used as needed. This search should help in that regard.
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Chapter 36: JIT compiler
JIT compilation, or just-in-time compilation, is an alternative approach to interpretation of code or ahead-of-time compilation. JIT compilation is used in the .NET framework. The CLR code (C#, F#, Visual Basic, etc.) is first compiled into something called Interpreted Language, or IL. This is lower level code that is closer to machine code, but is not platform specific. Rather, at runtime, this code is compiled into machine code for the relevant system.
Section 36.1: IL compilation sample
Simple Hello World Application:
using System;
namespace HelloWorld { class Program { static void Main(string[] args) { Console.WriteLine(“Hello World”); } } }
Equivalent IL Code (which will be JIT compiled)
// Microsoft (R) .NET Framework IL Disassembler. Version 4.6.1055.0 // Copyright (c) Microsoft Corporation. All rights reserved.
// Metadata version: v4.0.30319 .assembly extern mscorlib { .publickeytoken = (B7 7A 5C 56 19 34 E0 89 ) // .zV.4.. .ver 4:0:0:0 } .assembly HelloWorld { .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilationRelaxationsAttribute::.ctor(int32) = ( 01 00 08 00 00 00 00 00 ) .custom instance void [mscorlib]System.Runtime.CompilerServices.RuntimeCompatibilityAttribute::.ctor() = ( 01 00 01 00 54 02 16 57 72 61 70 4E 6F 6E 45 78 // ….T..WrapNonEx 63 65 70 74 69 6F 6E 54 68 72 6F 77 73 01 ) // ceptionThrows.
// — The following custom attribute is added automatically, do not uncomment ——- // .custom instance void [mscorlib]System.Diagnostics.DebuggableAttribute::.ctor(valuetype [mscorlib]System.Diagnostics.DebuggableAttribute/DebuggingModes) = ( 01 00 07 01 00 00 00 00 )
.custom instance void [mscorlib]System.Reflection.AssemblyTitleAttribute::.ctor(string) = ( 01 00 0A 48 65 6C 6C 6F 57 6F 72 6C 64 00 00 ) // …HelloWorld.. .custom instance void [mscorlib]System.Reflection.AssemblyDescriptionAttribute::.ctor(string) = ( 01 00 00 00 00 ) .custom instance void [mscorlib]System.Reflection.AssemblyConfigurationAttribute::.ctor(string) = ( 01 00 00 00 00 ) .custom instance void [mscorlib]System.Reflection.AssemblyCompanyAttribute::.ctor(string) = ( 01 00 00 00 00 )
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.custom instance void [mscorlib]System.Reflection.AssemblyProductAttribute::.ctor(string) = ( 01 00 0A 48 65 6C 6C 6F 57 6F 72 6C 64 00 00 ) // …HelloWorld.. .custom instance void [mscorlib]System.Reflection.AssemblyCopyrightAttribute::.ctor(string) = ( 01 00 12 43 6F 70 79 72 69 67 68 74 20 C2 A9 20 // …Copyright .. 20 32 30 31 37 00 00 ) // 2017.. .custom instance void [mscorlib]System.Reflection.AssemblyTrademarkAttribute::.ctor(string) = ( 01 00 00 00 00 ) .custom instance void [mscorlib]System.Runtime.InteropServices.ComVisibleAttribute::.ctor(bool) = ( 01 00 00 00 00 ) .custom instance void [mscorlib]System.Runtime.InteropServices.GuidAttribute::.ctor(string) = ( 01 00 24 33 30 38 62 33 64 38 36 2D 34 31 37 32 // ..$308b3d86-4172 2D 34 30 32 32 2D 61 66 63 63 2D 33 66 38 65 33 // -4022-afcc-3f8e3 32 33 33 63 35 62 30 00 00 ) // 233c5b0.. .custom instance void [mscorlib]System.Reflection.AssemblyFileVersionAttribute::.ctor(string) = ( 01 00 07 31 2E 30 2E 30 2E 30 00 00 ) // …1.0.0.0.. .custom instance void [mscorlib]System.Runtime.Versioning.TargetFrameworkAttribute::.ctor(string) = ( 01 00 1C 2E 4E 45 54 46 72 61 6D 65 77 6F 72 6B // ….NETFramework 2C 56 65 72 73 69 6F 6E 3D 76 34 2E 35 2E 32 01 // ,Version=v4.5.2. 00 54 0E 14 46 72 61 6D 65 77 6F 72 6B 44 69 73 // .T..FrameworkDis 70 6C 61 79 4E 61 6D 65 14 2E 4E 45 54 20 46 72 // playName..NET Fr 61 6D 65 77 6F 72 6B 20 34 2E 35 2E 32 ) // amework 4.5.2 .hash algorithm 0x00008004 .ver 1:0:0:0 } .module HelloWorld.exe // MVID: {2A7E1D59-1272-4B47-85F6-D7E1ED057831} .imagebase 0x00400000 .file alignment 0x00000200 .stackreserve 0x00100000 .subsystem 0x0003 // WINDOWS_CUI .corflags 0x00020003 // ILONLY 32BITPREFERRED // Image base: 0x0000021C70230000
// =============== CLASS MEMBERS DECLARATION ===================
.class private auto ansi beforefieldinit HelloWorld.Program extends [mscorlib]System.Object { .method private hidebysig static void Main(string[] args) cil managed { .entrypoint // Code size 13 (0xd) .maxstack 8 IL_0000: nop IL_0001: ldstr “Hello World” IL_0006: call void [mscorlib]System.Console::WriteLine(string) IL_000b: nop IL_000c: ret } // end of method Program::Main
.method public hidebysig specialname rtspecialname instance void .ctor() cil managed { // Code size 8 (0x8) .maxstack 8 IL_0000: ldarg.0 IL_0001: call instance void [mscorlib]System.Object::.ctor() IL_0006: nop IL_0007: ret } // end of method Program::.ctor
} // end of class HelloWorld.Program
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Generated with MS ILDASM tool (IL disassembler)
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Chapter 37: CLR Section 37.1: An introduction to Common Language Runtime The Common Language Runtime (CLR) is a virtual machine environment and part of the .NET Framework. It contains:
A portable bytecode language called Common Intermediate Language (abbreviated CIL, or IL) A Just-In-Time compiler that generates machine code A tracing garbage collector that provides automatic memory management Support for lightweight sub-processes called AppDomains Security mechanisms through the concepts of verifiable code and trust levels
Code that runs in the CLR is referred to as managed code to distinguish it from code running outside the CLR (usually native code) which is referred to as unmanaged code. There are various mechanisms that facilitate interoperability between managed and unmanaged code.
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Chapter 38: TPL Dataflow Section 38.1: Asynchronous Producer Consumer With A Bounded BuerBlock
var bufferBlock = new BufferBlock(new DataflowBlockOptions { BoundedCapacity = 1000 });
var cancellationToken = new CancellationTokenSource(TimeSpan.FromSeconds(10)).Token;
var producerTask = Task.Run(async () => { var random = new Random();
while (!cancellationToken.IsCancellationRequested) { var value = random.Next(); await bufferBlock.SendAsync(value, cancellationToken); } });
var consumerTask = Task.Run(async () => { while (await bufferBlock.OutputAvailableAsync()) { var value = bufferBlock.Receive(); Console.WriteLine(value); } });
await Task.WhenAll(producerTask, consumerTask);
Section 38.2: Posting to an ActionBlock and waiting for completion
// Create a block with an asynchronous action var block = new ActionBlock(async hostName => { IPAddress[] ipAddresses = await Dns.GetHostAddressesAsync(hostName); Console.WriteLine(ipAddresses[0]); });
block.Post(“google.com”); // Post items to the block’s InputQueue for processing block.Post(“reddit.com”); block.Post(“stackoverflow.com”);
block.Complete(); // Tell the block to complete and stop accepting new items await block.Completion; // Asynchronously wait until all items completed processingu
Section 38.3: Linking blocks to create a pipeline
var httpClient = new HttpClient();
// Create a block the accepts a uri and returns its contents as a string var downloaderBlock = new TransformBlock(
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async uri => await httpClient.GetStringAsync(uri));
// Create a block that accepts the content and prints it to the console var printerBlock = new ActionBlock( contents => Console.WriteLine(contents));
// Make the downloaderBlock complete the printerBlock when its completed. var dataflowLinkOptions = new DataflowLinkOptions {PropagateCompletion = true};
// Link the block to create a pipeline downloaderBlock.LinkTo(printerBlock, dataflowLinkOptions);
// Post urls to the first block which will pass their contents to the second one. downloaderBlock.Post(“http://youtube.com”); downloaderBlock.Post(“http://github.com”); downloaderBlock.Post(“http://twitter.com”);
downloaderBlock.Complete(); // Completion will propagate to printerBlock await printerBlock.Completion; // Only need to wait for the last block in the pipeline
Section 38.4: Synchronous Producer/Consumer with BuerBlock
public class Producer { private static Random random = new Random((int)DateTime.UtcNow.Ticks); //produce the value that will be posted to buffer block public double Produce ( ) { var value = random.NextDouble(); Console.WriteLine($”Producing value: {value}”); return value; } }
public class Consumer { //consume the value that will be received from buffer block public void Consume (double value) => Console.WriteLine($”Consuming value: {value}”); }
class Program { private static BufferBlock buffer = new BufferBlock(); static void Main (string[] args) { //start a task that will every 1 second post a value from the producer to buffer block var producerTask = Task.Run(async () => { var producer = new Producer(); while(true) { buffer.Post(producer.Produce()); await Task.Delay(1000); } }); //start a task that will recieve values from bufferblock and consume it var consumerTask = Task.Run(() => { var consumer = new Consumer(); while(true)
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{ consumer.Consume(buffer.Receive()); } });
Task.WaitAll(new[] { producerTask, consumerTask }); } }
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Chapter 39: Threading Section 39.1: Accessing form controls from other threads
If you want to change an attribute of a control such as a textbox or label from another thread than the GUI thread that created the control, you will have to invoke it or else you might get an error message stating:
“Cross-thread operation not valid: Control ‘control_name’ accessed from a thread other than the thread it was created on.”
Using this example code on a system.windows.forms form will cast an exception with that message:
private void button4_Click(object sender, EventArgs e) { Thread thread = new Thread(updatetextbox); thread.Start(); }
private void updatetextbox() { textBox1.Text = “updated”; // Throws exception }
Instead when you want to change a textbox’s text from within a thread that doesn’t own it use Control.Invoke or Control.BeginInvoke. You can also use Control.InvokeRequired to check if invoking the control is necessary.
private void updatetextbox() { if (textBox1.InvokeRequired) textBox1.BeginInvoke((Action)(() => textBox1.Text = “updated”)); else textBox1.Text = “updated”; }
If you need to do this often, you can write an extension for invokeable objects to reduce the amount of code necessary to make this check:
public static class Extensions { public static void BeginInvokeIfRequired(this ISynchronizeInvoke obj, Action action) { if (obj.InvokeRequired) obj.BeginInvoke(action, new object[0]); else action(); } }
And updating the textbox from any thread becomes a bit simpler:
private void updatetextbox() { textBox1.BeginInvokeIfRequired(() => textBox1.Text = “updated”); }
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Be aware that Control.BeginInvoke as used in this example is asynchronous, meaning that code coming after a call to Control.BeginInvoke can be run immedeately after, whether or not the passed delegate has been executed yet.
If you need to be sure that textBox1 is updated before continuing, use Control.Invoke instead, which will block the calling thread until your delegate has been executed. Do note that this approach can slow your code down significantly if you make many invoke calls and note that it will deadlock your application if your GUI thread is waiting for the calling thread to complete or release a held resource.
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Chapter 40: Process and Thread anity setting
Parameter
affinity
integer that describes the set of processors on which the process is allowed to run. For example, on a 8 processor system if you want your process to be executed only on processors 3 and 4 than you choose affinity like this : 00001100 which equals 12
Details
Section 40.1: Get process anity mask
public static int GetProcessAffinityMask(string processName = null) { Process myProcess = GetProcessByName(ref processName);
int processorAffinity = (int)myProcess.ProcessorAffinity; Console.WriteLine(“Process {0} Affinity Mask is : {1}”, processName, FormatAffinity(processorAffinity));
return processorAffinity; }
public static Process GetProcessByName(ref string processName) { Process myProcess; if (string.IsNullOrEmpty(processName)) { myProcess = Process.GetCurrentProcess(); processName = myProcess.ProcessName; } else { Process[] processList = Process.GetProcessesByName(processName); myProcess = processList[0]; } return myProcess; }
private static string FormatAffinity(int affinity) { return Convert.ToString(affinity, 2).PadLeft(Environment.ProcessorCount, ‘0’); } }
Example of usage :
private static void Main(string[] args) { GetProcessAffinityMask();
Console.ReadKey(); } // Output: // Process Test.vshost Affinity Mask is : 11111111
Section 40.2: Set process anity mask
public static void SetProcessAffinityMask(int affinity, string processName = null)
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{ Process myProcess = GetProcessByName(ref processName);
Console.WriteLine(“Process {0} Old Affinity Mask is : {1}”, processName, FormatAffinity((int)myProcess.ProcessorAffinity));
myProcess.ProcessorAffinity = new IntPtr(affinity); Console.WriteLine(“Process {0} New Affinity Mask is : {1}”, processName, FormatAffinity((int)myProcess.ProcessorAffinity)); }
Example of usage :
private static void Main(string[] args) { int newAffinity = Convert.ToInt32(“10101010”, 2); SetProcessAffinityMask(newAffinity);
Console.ReadKey(); } // Output : // Process Test.vshost Old Affinity Mask is : 11111111 // Process Test.vshost New Affinity Mask is : 10101010
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Chapter 41: Parallel processing using .Net framework
This Topic is about Multi core programming using Task Parallel Library with .NET framework. The task parallel library allows you to write code which is human readable and adjusts itself with the number of Cores available. So you can be sure that your software would auto-upgrade itself with the upgrading environment.
Section 41.1: Parallel Extensions
Parallel extensions have been introduced along with the Task Parallel Library to achieve data Parallelism. Data parallelism refers to scenarios in which the same operation is performed concurrently (that is, in parallel) on elements in a source collection or array. The .NET provides new constructs to achieve data parallelism by using Parallel.For and Parallel.Foreach constructs.
//Sequential version
foreach (var item in sourcecollection){
Process(item);
}
// Parallel equivalent
Parallel.foreach(sourcecollection, item => Process(item));
The above mentioned Parallel.ForEach construct utilizes the multiple cores and thus enhances the performance in the same fashion.
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Chapter 42: Task Parallel Library (TPL) Section 42.1: Basic producer-consumer loop (BlockingCollection)
var collection = new BlockingCollection(5); var random = new Random();
var producerTask = Task.Run(() => { for(int item=1; item { foreach(var item in collection.GetConsumingEnumerable()) { Console.WriteLine(“Consumed: ” + item); Thread.Sleep(random.Next(10,1000)); } Console.WriteLine(“Consumer completed!”); }); Task.WaitAll(producerTask, consumerTask); Console.WriteLine(“Everything completed!”);
Section 42.2: Parallel.Invoke
var actions = Enumerable.Range(1, 10).Select(n => new Action(() => { Console.WriteLine(“I’m task ” + n); if((n & 1) == 0) throw new Exception(“Exception from task ” + n); })).ToArray();
try { Parallel.Invoke(actions); } catch(AggregateException ex) { foreach(var inner in ex.InnerExceptions) Console.WriteLine(“Task failed: ” + inner.Message);
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}
Section 42.3: Task: Returning a value
Task that return a value has return type of Task where TResult is the type of value that needs to be returned. You can query the outcome of a Task by its Result property.
Task t = Task.Run(() => { int sum = 0;
for(int i = 0; i 0, // initial value, (num, state, localSum) => num + localSum, localSum => Interlocked.Add(ref total, localSum)); return total; // total = 50005000 }
Section 42.5: Parallel.For
This example uses Parallel.For to calculate the sum of the numbers between 1 and 10000 by using multiple threads. To achieve thread-safety, Interlocked.Add is used to sum the numbers.
using System.Threading;
int Foo() { int total = 0; Parallel.For(1, 10001,
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() => 0, // initial value, (num, state, localSum) => num + localSum, localSum => Interlocked.Add(ref total, localSum)); return total; // total = 50005000 }
Section 42.6: Task: basic instantiation and Wait
A task can be created by directly instantiating the Task class…
var task = new Task(() => { Console.WriteLine(“Task code starting…”); Thread.Sleep(2000); Console.WriteLine(“…task code ending!”); });
Console.WriteLine(“Starting task…”); task.Start(); task.Wait(); Console.WriteLine(“Task completed!”);
…or by using the static Task.Run method:
Console.WriteLine(“Starting task…”); var task = Task.Run(() => { Console.WriteLine(“Task code starting…”); Thread.Sleep(2000); Console.WriteLine(“…task code ending!”); }); task.Wait(); Console.WriteLine(“Task completed!”);
Note that only in the first case it is necessary to explicitly invoke Start.
Section 42.7: Task.WhenAll
var random = new Random(); IEnumerable<Task> tasks = Enumerable.Range(1, 5).Select(n => Task.Run(() => { Console.WriteLine(“I’m task ” + n); return n; }));
Task task = Task.WhenAll(tasks); int[] results = await task;
Console.WriteLine(string.Join(“,”, results.Select(n => n.ToString()))); // Output: 1,2,3,4,5
Section 42.8: Flowing execution context with AsyncLocal
When you need to pass some data from the parent task to its children tasks, so it logically flows with the execution, use AsyncLocal class:
void Main() {
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AsyncLocal user = new AsyncLocal(); user.Value = “initial user”; // this does not affect other tasks – values are local relative to the branches of execution flow Task.Run(() => user.Value = “user from another task”); var task1 = Task.Run(() => { Console.WriteLine(user.Value); // outputs “initial user” Task.Run(() => { // outputs “initial user” – value has flown from main method to this task without being changed Console.WriteLine(user.Value); }).Wait();
user.Value = “user from task1”;
Task.Run(() => { // outputs “user from task1” – value has flown from main method to task1 // than value was changed and flown to this task. Console.WriteLine(user.Value); }).Wait(); }); task1.Wait(); // outputs “initial user” – changes do not propagate back upstream the execution flow Console.WriteLine(user.Value); }
Note: As can be seen from the example above AsynLocal.Value has copy on read semantic, but if you flow some reference type and change its properties you will affect other tasks. Hence, best practice with AsyncLocal is to use value types or immutable types.
Section 42.9: Parallel.ForEach in VB.NET
For Each row As DataRow In FooDataTable.Rows Me.RowsToProcess.Add(row) Next
Dim myOptions As ParallelOptions = New ParallelOptions() myOptions.MaxDegreeOfParallelism = environment.processorcount
Parallel.ForEach(RowsToProcess, myOptions, Sub(currentRow, state) ProcessRowParallel(currentRow, state) End Sub)
Section 42.10: Task: WaitAll and variable capturing
var tasks = Enumerable.Range(1, 5).Select(n => new Task(() => { Console.WriteLine(“I’m task ” + n); return n; })).ToArray();
foreach(var task in tasks) task.Start(); Task.WaitAll(tasks);
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foreach(var task in tasks) Console.WriteLine(task.Result);
Section 42.11: Task: WaitAny
var allTasks = Enumerable.Range(1, 5).Select(n => new Task(() => n)).ToArray(); var pendingTasks = allTasks.ToArray();
foreach(var task in allTasks) task.Start();
while(pendingTasks.Length > 0) { var finishedTask = pendingTasks[Task.WaitAny(pendingTasks)]; Console.WriteLine(“Task {0} finished”, finishedTask.Result); pendingTasks = pendingTasks.Except(new[] {finishedTask}).ToArray(); }
Task.WaitAll(allTasks);
Note: The final WaitAll is necessary becasue WaitAny does not cause exceptions to be observed. Section 42.12: Task: handling exceptions (using Wait)
var task1 = Task.Run(() => { Console.WriteLine(“Task 1 code starting…”); throw new Exception(“Oh no, exception from task 1!!”); });
var task2 = Task.Run(() => { Console.WriteLine(“Task 2 code starting…”); throw new Exception(“Oh no, exception from task 2!!”); });
Console.WriteLine(“Starting tasks…”); try { Task.WaitAll(task1, task2); } catch(AggregateException ex) { Console.WriteLine(“Task(s) failed!”); foreach(var inner in ex.InnerExceptions) Console.WriteLine(inner.Message); }
Console.WriteLine(“Task 1 status is: ” + task1.Status); //Faulted Console.WriteLine(“Task 2 status is: ” + task2.Status); //Faulted
Section 42.13: Task: handling exceptions (without using Wait)
var task1 = Task.Run(() => { Console.WriteLine(“Task 1 code starting…”); throw new Exception(“Oh no, exception from task 1!!”); });
var task2 = Task.Run(() =>
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{ Console.WriteLine(“Task 2 code starting…”); throw new Exception(“Oh no, exception from task 2!!”); });
var tasks = new[] {task1, task2};
Console.WriteLine(“Starting tasks…”); while(tasks.All(task => !task.IsCompleted));
foreach(var task in tasks) { if(task.IsFaulted) Console.WriteLine(“Task failed: ” + task.Exception.InnerExceptions.First().Message); }
Console.WriteLine(“Task 1 status is: ” + task1.Status); //Faulted Console.WriteLine(“Task 2 status is: ” + task2.Status); //Faulted
Section 42.14: Task: cancelling using CancellationToken
var cancellationTokenSource = new CancellationTokenSource(); var cancellationToken = cancellationTokenSource.Token;
var task = new Task((state) => { int i = 1; var myCancellationToken = (CancellationToken)state; while(true) { Console.Write(“{0} “, i++); Thread.Sleep(1000); myCancellationToken.ThrowIfCancellationRequested(); } }, cancellationToken: cancellationToken, state: cancellationToken);
Console.WriteLine(“Counting to infinity. Press any key to cancel!”); task.Start(); Console.ReadKey();
cancellationTokenSource.Cancel(); try { task.Wait(); } catch(AggregateException ex) { ex.Handle(inner => inner is OperationCanceledException); }
Console.WriteLine($”{Environment.NewLine}You have cancelled! Task status is: {task.Status}”); //Canceled
As an alternative to ThrowIfCancellationRequested, the cancellation request can be detected with IsCancellationRequested and a OperationCanceledException can be thrown manually:
//New task delegate
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int i = 1; var myCancellationToken = (CancellationToken)state; while(!myCancellationToken.IsCancellationRequested) { Console.Write(“{0} “, i++); Thread.Sleep(1000); } Console.WriteLine($”{Environment.NewLine}Ouch, I have been cancelled!!”); throw new OperationCanceledException(myCancellationToken);
Note how the cancellation token is passed to the task constructor in the cancellationToken parameter. This is needed so that the task transitions to the Canceled state, not to the Faulted state, when ThrowIfCancellationRequested is invoked. Also, for the same reason, the cancellation token is explicitly supplied in the constructor of OperationCanceledException in the second case.
Section 42.15: Task.WhenAny
var random = new Random(); IEnumerable<Task> tasks = Enumerable.Range(1, 5).Select(n => Task.Run(async() => { Console.WriteLine(“I’m task ” + n); await Task.Delay(random.Next(10,1000)); return n; }));
Task<Task> whenAnyTask = Task.WhenAny(tasks); Task completedTask = await whenAnyTask; Console.WriteLine(“The winner is: task ” + await completedTask);
await Task.WhenAll(tasks); Console.WriteLine(“All tasks finished!”);
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Chapter 43: Task Parallel Library (TPL) API Overviews Section 43.1: Perform work in response to a button click and update the UI
This example demonstrates how you can respond to a button click by performing some work on a worker thread and then update the user interface to indicate completion
void MyButton_OnClick(object sender, EventArgs args) { Task.Run(() => // Schedule work using the thread pool { System.Threading.Thread.Sleep(5000); // Sleep for 5 seconds to simulate work. }) .ContinueWith(p => // this continuation contains the ‘update’ code to run on the UI thread { this.TextBlock_ResultText.Text = “The work completed at ” + DateTime.Now.ToString() }, TaskScheduler.FromCurrentSynchronizationContext()); // make sure the update is run on the UI thread.
}
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Chapter 44: Synchronization Contexts Section 44.1: Execute code on the UI thread after performing background work
This example shows how to update a UI component from a background thread by using a SynchronizationContext
void Button_Click(object sender, EventArgs args) { SynchronizationContext context = SynchronizationContext.Current; Task.Run(() => { for(int i = 0; i < 10; i++) { Thread.Sleep(500); //simulate work being done context.Post(ShowProgress, "Work complete on item " + i); } } }
void UpdateCallback(object state) { // UI can be safely updated as this method is only called from the UI thread this.MyTextBox.Text = state as string; }
In this example, if you tried to directly update MyTextBox.Text inside the for loop, you would get a threading error. By posting the UpdateCallback action to the SynchronizationContext, the text box is updated on the same thread as the rest of the UI.
In practice, progress updates should be performed using an instance of System.IProgress. The default implementation System.Progress automatically captures the synchronisation context it is created on.
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Chapter 45: Memory management Section 45.1: Use SafeHandle when wrapping unmanaged resources
When writing wrappers for unmanaged resources, you should subclass SafeHandle rather than trying to implement IDisposable and a finalizer yourself. Your SafeHandle subclass should be as small and simple as possible to minimize the chance of a handle leak. This likely means that your SafeHandle implementation would an internal implementation detail of a class which wraps it to provide a usable API. This class ensures that, even if a program leaks your SafeHandle instance, your unmanaged handle is released.
using System.Runtime.InteropServices;
class MyHandle : SafeHandle { public override bool IsInvalid => handle == IntPtr.Zero; public MyHandle() : base(IntPtr.Zero, true) { }
public MyHandle(int length) : this() { SetHandle(Marshal.AllocHGlobal(length)); }
protected override bool ReleaseHandle() { Marshal.FreeHGlobal(handle); return true; } }
Disclaimer: This example is an attempt to show how to guard a managed resource with SafeHandle which implements IDisposable for you and configures finalizers appropriately. It is very contrived and likely pointless to allocate a chunk of memory in this manner.
Section 45.2: Unmanaged Resources
When we talk about the GC and the “heap”, we’re really talking about what’s called the managed heap. Objects on the managed heap can access resources not on the managed heap, for example, when writing to or reading from a file. Unexpected behavior can occur when, a file is opened for reading and then an exception occurs, preventing the file handle from closing as it normally would. For this reason, .NET requires that unmanaged resources implement the IDisposable interface. This interface has a single method called Dispose with no parameters:
public interface IDisposable { Dispose(); }
When handling unmanaged resources, you should make sure that they are properly disposed. You can do this by explicitly calling Dispose() in a finally block, or with a using statement.
StreamReader sr; string textFromFile; string filename = “SomeFile.txt”; try
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{ sr = new StreamReader(filename); textFromFile = sr.ReadToEnd(); } finally { if (sr != null) sr.Dispose(); }
or
string textFromFile; string filename = “SomeFile.txt”;
using (StreamReader sr = new Streamreader(filename)) { textFromFile = sr.ReadToEnd(); }
The latter is the preferred method, and is automatically expanded to the former during compilation.
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Chapter 46: Garbage Collection
In .Net, objects created with new() are allocated on the managed heap. These objects are never explicitly finalized by the program that uses them; instead, this process is controlled by the .Net Garbage Collector.
Some of the examples below are “lab cases” to show the Garbage Collector at work and some significant details of its behavior, while other focus on how to prepare classes for proper handling by the Garbage Collector.
Section 46.1: A basic example of (garbage) collection
Given the following class:
public class FinalizableObject { public FinalizableObject() { Console.WriteLine(“Instance initialized”); }
~FinalizableObject() { Console.WriteLine(“Instance finalized”); } }
A program that creates an instance, even without using it:
new FinalizableObject(); // Object instantiated, ready to be used
Produces the following output:
.FinalizableObject initialized
If nothing else happens, the object is not finalized until the program ends (which frees all objects on the managed heap, finalizing these in the process).
It is possible to force the Garbage Collector to run at a given point, as follows:
new FinalizableObject(); // Object instantiated, ready to be used GC.Collect();
Which produces the following result:
.FinalizableObject initialized .FinalizableObject finalized
This time, as soon as the Garbage Collector was invoked, the unused (aka “dead”) object was finalized and freed from the managed heap.
Section 46.2: Live objects and dead objects – the basics
Rule of thumb: when garbage collection occurs, “live objects” are those still in use, while “dead objects” are those no longer used (any variable or field referencing them, if any, has gone out of scope before the collection occurs).
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In the following example (for convenience, FinalizableObject1 and FinalizableObject2 are subclasses of FinalizableObject from the example above and thus inherit the initialization / finalization message behavior):
var obj1 = new FinalizableObject1(); // Finalizable1 instance allocated here var obj2 = new FinalizableObject2(); // Finalizable2 instance allocated here obj1 = null; // No more references to the Finalizable1 instance GC.Collect();
The output will be:
.FinalizableObject1 initialized .FinalizableObject2 initialized .FinalizableObject1 finalized
At the time when the Garbage Collector is invoked, FinalizableObject1 is a dead object and gets finalized, while FinalizableObject2 is a live object and it is kept on the managed heap.
Section 46.3: Multiple dead objects
What if two (or several) otherwise dead objects reference one another? This is shown in the example below, supposing that OtherObject is a public property of FinalizableObject:
var obj1 = new FinalizableObject1(); var obj2 = new FinalizableObject2(); obj1.OtherObject = obj2; obj2.OtherObject = obj1; obj1 = null; // Program no longer references Finalizable1 instance obj2 = null; // Program no longer references Finalizable2 instance // But the two objects still reference each other GC.Collect();
This produces the following output:
.FinalizedObject1 initialized .FinalizedObject2 initialized .FinalizedObject1 finalized .FinalizedObject2 finalized
The two objects are finalized and freed from the managed heap despite referencing each other (because no other reference exists to any of them from an actually live object).
Section 46.4: Weak References
Weak references are… references, to other objects (aka “targets”), but “weak” as they do not prevent those objects from being garbage-collected. In other words, weak references do not count when the Garbage Collector evaluates objects as “live” or “dead”.
The following code:
var weak = new WeakReference(new FinalizableObject()); GC.Collect();
Produces the output:
.FinalizableObject initialized
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.FinalizableObject finalized
The object is freed from the managed heap despite being referenced by the WeakReference variable (still in scope when the Garbage collector was invoked).
Consequence #1: at any time, it is unsafe to assume whether a WeakReference target is still allocated on the managed heap or not.
Consequence #2: whenever a program needs to access the target of a Weakreference, code should be provided for both cases, of the target being still allocated or not. The method to access the target is TryGetTarget:
var target = new object(); // Any object will do as target var weak = new WeakReference(target); // Create weak reference target = null; // Drop strong reference to the target
// … Many things may happen in-between
// Check whether the target is still available if(weak.TryGetTarget(out target)) { // Use re-initialized target variable // To do whatever the target is needed for } else { // Do something when there is no more target object // The target variable value should not be used here }
The generic version of WeakReference is available since .Net 4.5. All framework versions provide a non-generic, untyped version that is built in the same way and checked as follows:
var target = new object(); // Any object will do as target var weak = new WeakReference(target); // Create weak reference target = null; // Drop strong reference to the target
// … Many things may happen in-between
// Check whether the target is still available if (weak.IsAlive) { target = weak.Target;
// Use re-initialized target variable // To do whatever the target is needed for } else { // Do something when there is no more target object // The target variable value should not be used here }
Section 46.5: Dispose() vs. finalizers
Implement Dispose() method (and declare the containing class as IDisposable) as a means to ensure any memory- heavy resources are freed as soon as the object is no longer used. The “catch” is that there is no strong guarantee the the Dispose() method would ever be invoked (unlike finalizers that always get invoked at the end of the life of the object).
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One scenario is a program calling Dispose() on objects it explicitly creates:
private void SomeFunction() { // Initialize an object that uses heavy external resources var disposableObject = new ClassThatImplementsIDisposable();
// … Use that object
// Dispose as soon as no longer used disposableObject.Dispose();
// … Do other stuff
// The disposableObject variable gets out of scope here // The object will be finalized later on (no guarantee when) // But it no longer holds to the heavy external resource after it was disposed }
Another scenario is declaring a class to be instantiated by the framework. In this case the new class usually inherits a base class, for instance in MVC one creates a controller class as a subclass of System.Web.Mvc.ControllerBase. When the base class implements IDisposable interface, this is a good hint that Dispose() would be invoked properly by the framework – but again there is no strong guarantee.
Thus Dispose() is not a substitute for a finalizer; instead, the two should be used for different purposes:
A finalizer eventually frees resources to avoid memory leaks that would occur otherwise Dispose() frees resources (possibly the same ones) as soon as these are no longer needed, to ease pressure on overall memory allocation.
Section 46.6: Proper disposal and finalization of objects
As Dispose() and finalizers are aimed to different purposes, a class managing external memory-heavy resources should implement both of them. The consequence is writing the class so that it handles well two possible scenarios:
When only the finalizer is invoked When Dispose() is invoked first and later the finalizer is invoked as well
One solution is writing the cleanup code in such a way that running it once or twice would produce the same result as running it only once. Feasibility depends on the nature of the cleanup, for instance:
Closing an already closed database connection would probably have no effect so it works Updating some “usage count” is dangerous and would produce a wrong result when called twice instead of once.
A safer solution is ensuring by design that the cleanup code is called once and only once whatever the external context. This can be achieved the “classic way” using a dedicated flag:
public class DisposableFinalizable1: IDisposable { private bool disposed = false;
~DisposableFinalizable1() { Cleanup(); }
public void Dispose() { Cleanup(); }
private void Cleanup()
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{ if(!disposed) { // Actual code to release resources gets here, then disposed = true; } } }
Alternately, the Garbage Collector provides a specific method SuppressFinalize() that allows skipping the finalizer after Dispose has been invoked:
public class DisposableFinalizable2 : IDisposable { ~DisposableFinalizable2() { Cleanup(); }
public void Dispose() { Cleanup(); GC.SuppressFinalize(this); }
private void Cleanup() { // Actual code to release resources gets here } }
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Chapter 47: Exceptions Section 47.1: Catching and rethrowing caught exceptions
When you want to catch an exception and do something, but you can’t continue execution of the current block of code because of the exception, you may want to rethrow the exception to the next exception handler in the call stack. There are good ways and bad ways to do this.
private static void AskTheUltimateQuestion() { try { var x = 42; var y = x / (x – x); // will throw a DivideByZeroException
// IMPORTANT NOTE: the error in following string format IS intentional // and exists to throw an exception to the FormatException catch, below Console.WriteLine(“The secret to life, the universe, and everything is {1}”, y); } catch (DivideByZeroException) { // we do not need a reference to the exception Console.WriteLine(“Dividing by zero would destroy the universe.”);
// do this to preserve the stack trace: throw; } catch (FormatException ex) { // only do this if you need to change the type of the Exception to be thrown // and wrap the inner Exception
// remember that the stack trace of the outer Exception will point to the // next line
// you’ll need to examine the InnerException property to get the stack trace // to the line that actually started the problem
throw new InvalidOperationException(“Watch your format string indexes.”, ex); } catch (Exception ex) { Console.WriteLine(“Something else horrible happened. The exception: ” + ex.Message);
// do not do this, because the stack trace will be changed to point to // this location instead of the location where the exception // was originally thrown: throw ex; } }
static void Main() { try { AskTheUltimateQuestion(); } catch { // choose this kind of catch if you don’t need any information about
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// the exception that was caught
// this block “eats” all exceptions instead of rethrowing them } }
You can filter by exception type and even by exception properties (new in C# 6.0, a bit longer available in VB.NET (citation needed)):
Documentation/C#/new features
Section 47.2: Using a finally block
The finally { … } block of a try-finally or try-catch-finally will always execute, regardless of whether an exception occurred or not (except when a StackOverflowException has been thrown or call has been made to Environment.FailFast()).
It can be utilized to free or clean up resources acquired in the try { … } block safely.
Console.Write(“Please enter a filename: “); string filename = Console.ReadLine();
Stream fileStream = null;
try { fileStream = File.Open(filename); } catch (FileNotFoundException) { Console.WriteLine(“File ‘{0}’ could not be found.”, filename); } finally { if (fileStream != null) { fileStream.Dispose(); } }
Section 47.3: Exception Filters
Since C# 6.0 exceptions can be filtered using the when operator.
This is similar to using a simple if but does not unwind the stack if the condition inside the when is not met.
Example
try { // … } catch (Exception e) when (e.InnerException != null) // Any condition can go in here. { // … }
The same info can be found in the C# 6.0 Features here: Exception filters
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Section 47.4: Rethrowing an exception within a catch block
Within a catch block the throw keyword can be used on its own, without specifying an exception value, to rethrow the exception which was just caught. Rethrowing an exception allows the original exception to continue up the exception handling chain, preserving its call stack or associated data:
try {…} catch (Exception ex) { // Note: the ex variable is *not* used throw; }
A common anti-pattern is to instead throw ex, which has the effect of limiting the next exception handler’s view of the stack trace:
try {…} catch (Exception ex) { // Note: the ex variable is thrown // future stack traces of the exception will not see prior calls throw ex; }
In general using throw ex isn’t desirable, as future exception handlers which inspect the stack trace will only be able to see calls as far back as throw ex. By omitting the ex variable, and using the throw keyword alone the original exception will “bubble-up”.
Section 47.5: Throwing an exception from a dierent method while preserving its information
Occasionally you’d want to catch an exception and throw it from a different thread or method while preserving the original exception stack. This can be done with ExceptionDispatchInfo:
using System.Runtime.ExceptionServices;
void Main() { ExceptionDispatchInfo capturedException = null; try { throw new Exception(); } catch (Exception ex) { capturedException = ExceptionDispatchInfo.Capture(ex); } Foo(capturedException); }
void Foo(ExceptionDispatchInfo exceptionDispatchInfo) { // Do stuff
if (capturedException != null) { // Exception stack trace will show it was thrown from Main() and not from Foo() exceptionDispatchInfo.Throw(); }
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}
Section 47.6: Catching an exception
Code can and should throw exceptions in exceptional circumstances. Examples of this include:
Attempting to read past the end of a stream Not having necessary permissions to access a file Attempting to perform an invalid operation, such as dividing by zero A timeout occurring when downloading a file from the internet
The caller can handle these exceptions by “catching” them, and should only do so when:
It can actually resolve the exceptional circumstance or recover appropriately, or; It can provide additional context to the exception that would be useful if the exception needs to be re-thrown (re-thrown exceptions are caught by exception handlers further up the call stack)
It should be noted that choosing not to catch an exception is perfectly valid if the intention is for it to be handled at a higher level.
Catching an exception is done by wrapping the potentially-throwing code in a try { … } block as follows, and catching the exceptions it’s able to handle in a catch (ExceptionType) { … } block:
Console.Write(“Please enter a filename: “); string filename = Console.ReadLine();
Stream fileStream;
try { fileStream = File.Open(filename); } catch (FileNotFoundException) { Console.WriteLine(“File ‘{0}’ could not be found.”, filename); }
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Chapter 48: System.Diagnostics Section 48.1: Run shell commands
string strCmdText = “/C copy /b Image1.jpg + Archive.rar Image2.jpg”; System.Diagnostics.Process.Start(“CMD.exe”,strCmdText);
This is to hide the cmd window.
System.Diagnostics.Process process = new System.Diagnostics.Process(); System.Diagnostics.ProcessStartInfo startInfo = new System.Diagnostics.ProcessStartInfo(); startInfo.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden; startInfo.FileName = “cmd.exe”; startInfo.Arguments = “/C copy /b Image1.jpg + Archive.rar Image2.jpg”; process.StartInfo = startInfo; process.Start();
Section 48.2: Send Command to CMD and Receive Output
This method allows a command to be sent to Cmd.exe, and returns the standard output (including standard error) as a string:
private static string SendCommand(string command) { var cmdOut = string.Empty; var startInfo = new ProcessStartInfo(“cmd”, command) { WorkingDirectory = @”C:WindowsSystem32″, // Directory to make the call from WindowStyle = ProcessWindowStyle.Hidden, // Hide the window UseShellExecute = false, // Do not use the OS shell to start the process CreateNoWindow = true, // Start the process in a new window RedirectStandardOutput = true, // This is required to get STDOUT RedirectStandardError = true // This is required to get STDERR };
var p = new Process {StartInfo = startInfo};
p.Start();
p.OutputDataReceived += (x, y) => cmdOut += y.Data; p.ErrorDataReceived += (x, y) => cmdOut += y.Data; p.BeginOutputReadLine(); p.BeginErrorReadLine(); p.WaitForExit(); return cmdOut; }
Usage
var servername = “SVR-01.domain.co.za”; var currentUsers = SendCommand($”/C QUERY USER /SERVER:{servername}”)
Output
string currentUsers = “USERNAME SESSIONNAME ID STATE IDLE TIME LOGON TIME Joe.Bloggs ica-cgp#0 2
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Active 24692+13:29 25/07/2016 07:50 Jim.McFlannegan ica-cgp#1 3 Active . 25/07/2016 08:33 Andy.McAnderson ica-cgp#2 4 Active . 25/07/2016 08:54 John.Smith ica-cgp#4 5 Active 14 25/07/2016 08:57 Bob.Bobbington ica-cgp#5 6 Active 24692+13:29 25/07/2016 09:05 Tim.Tom ica-cgp#6 7 Active . 25/07/2016 09:08 Bob.Joges ica-cgp#7 8 Active 24692+13:29 25/07/2016 09:13”
On some occasions, access to the server in question may be restricted to certain users. If you have the login credentials for this user, then it is possible to send queries with this method:
private static string SendCommand(string command) { var cmdOut = string.Empty; var startInfo = new ProcessStartInfo(“cmd”, command) { WorkingDirectory = @”C:WindowsSystem32″, WindowStyle = ProcessWindowStyle.Hidden, // This does not actually work in conjunction with “runas” – the console window will still appear! UseShellExecute = false, CreateNoWindow = true, RedirectStandardOutput = true, RedirectStandardError = true,
Verb = “runas”, Domain = “doman1.co.za”, UserName = “administrator”, Password = GetPassword() };
var p = new Process {StartInfo = startInfo};
p.Start();
p.OutputDataReceived += (x, y) => cmdOut += y.Data; p.ErrorDataReceived += (x, y) => cmdOut += y.Data; p.BeginOutputReadLine(); p.BeginErrorReadLine(); p.WaitForExit(); return cmdOut; }
Getting the password:
static SecureString GetPassword() { var plainText = “password123”; var ss = new SecureString(); foreach (char c in plainText) { ss.AppendChar(c); }
return ss; }
Notes
Both of the above methods will return a concatenation of STDOUT and STDERR, as OutputDataReceived and ErrorDataReceived are both appending to the same variable – cmdOut.
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Section 48.3: Stopwatch
This example shows how Stopwatch can be used to benchmark a block of code.
using System; using System.Diagnostics; public class Benchmark : IDisposable { private Stopwatch sw;
public Benchmark() { sw = Stopwatch.StartNew(); }
public void Dispose() { sw.Stop(); Console.WriteLine(sw.Elapsed); } }
public class Program { public static void Main() { using (var bench = new Benchmark()) { Console.WriteLine(“Hello World”); } } }
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Chapter 49: Encryption / Cryptography Section 49.1: Encryption and Decryption using Cryptography (AES)
Decryption Code
public static string Decrypt(string cipherText) { if (cipherText == null) return null;
byte[] cipherBytes = Convert.FromBase64String(cipherText); using (Aes encryptor = Aes.Create()) { Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(CryptKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 }); encryptor.Key = pdb.GetBytes(32); encryptor.IV = pdb.GetBytes(16);
using (MemoryStream ms = new MemoryStream()) { using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateDecryptor(), CryptoStreamMode.Write)) { cs.Write(cipherBytes, 0, cipherBytes.Length); cs.Close(); }
cipherText = Encoding.Unicode.GetString(ms.ToArray()); } } return cipherText; }
Encryption Code
public static string Encrypt(string cipherText) { if (cipherText == null) return null; byte[] clearBytes = Encoding.Unicode.GetBytes(cipherText); using (Aes encryptor = Aes.Create()) { Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(CryptKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 }); encryptor.Key = pdb.GetBytes(32); encryptor.IV = pdb.GetBytes(16);
using (MemoryStream ms = new MemoryStream()) { using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write)) { cs.Write(clearBytes, 0, clearBytes.Length); cs.Close(); }
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cipherText = Convert.ToBase64String(ms.ToArray()); } } return cipherText; }
Usage
var textToEncrypt = “TestEncrypt”;
var encrypted = Encrypt(textToEncrypt);
var decrypted = Decrypt(encrypted);
Section 49.2: RijndaelManaged
Required Namespace: System.Security.Cryptography
private class Encryption { private const string SecretKey = “topSecretKeyusedforEncryptions”; private const string SecretIv = “secretVectorHere”; public string Encrypt(string data) { return string.IsNullOrEmpty(data) ? data : Convert.ToBase64String(this.EncryptStringToBytesAes(data, this.GetCryptographyKey(), this.GetCryptographyIv())); } public string Decrypt(string data) { return string.IsNullOrEmpty(data) ? data : this.DecryptStringFromBytesAes(Convert.FromBase64String(data), this.GetCryptographyKey(), this.GetCryptographyIv()); } private byte[] GetCryptographyKey() { return Encoding.ASCII.GetBytes(SecretKey.Replace(‘e’, ‘!’)); } private byte[] GetCryptographyIv() { return Encoding.ASCII.GetBytes(SecretIv.Replace(‘r’, ‘!’)); } private byte[] EncryptStringToBytesAes(string plainText, byte[] key, byte[] iv) { MemoryStream encrypt; RijndaelManaged aesAlg = null; try { aesAlg = new RijndaelManaged { Key = key, IV = iv }; var encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV); encrypt = new MemoryStream(); using (var csEncrypt = new CryptoStream(encrypt, encryptor, CryptoStreamMode.Write)) { using (var swEncrypt = new StreamWriter(csEncrypt)) { swEncrypt.Write(plainText); } }
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} finally { aesAlg?.Clear(); } return encrypt.ToArray(); } private string DecryptStringFromBytesAes(byte[] cipherText, byte[] key, byte[] iv) { RijndaelManaged aesAlg = null; string plaintext; try { aesAlg = new RijndaelManaged { Key = key, IV = iv }; var decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV); using (var msDecrypt = new MemoryStream(cipherText)) { using (var csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read)) { using (var srDecrypt = new StreamReader(csDecrypt)) plaintext = srDecrypt.ReadToEnd(); } } } finally { aesAlg?.Clear(); } return plaintext; } }
Usage
var textToEncrypt = “hello World”;
var encrypted = new Encryption().Encrypt(textToEncrypt); //-> zBmW+FUxOvdbpOGm9Ss/vQ==
var decrypted = new Encryption().Decrypt(encrypted); //-> hello World
Note:
Rijndael is the predecessor of the standard symmetric cryptographic algorithm AES.
Section 49.3: Encrypt and decrypt data using AES (in C#)
using System; using System.IO; using System.Security.Cryptography;
namespace Aes_Example { class AesExample { public static void Main() { try { string original = “Here is some data to encrypt!”;
// Create a new instance of the Aes class. // This generates a new key and initialization vector (IV). using (Aes myAes = Aes.Create())
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{ // Encrypt the string to an array of bytes. byte[] encrypted = EncryptStringToBytes_Aes(original, myAes.Key, myAes.IV);
// Decrypt the bytes to a string. string roundtrip = DecryptStringFromBytes_Aes(encrypted, myAes.Key, myAes.IV);
//Display the original data and the decrypted data. Console.WriteLine(“Original: {0}”, original); Console.WriteLine(“Round Trip: {0}”, roundtrip); } } catch (Exception e) { Console.WriteLine(“Error: {0}”, e.Message); } }
static byte[] EncryptStringToBytes_Aes(string plainText, byte[] Key, byte[] IV) { // Check arguments. if (plainText == null || plainText.Length <= 0) throw new ArgumentNullException("plainText"); if (Key == null || Key.Length <= 0) throw new ArgumentNullException("Key"); if (IV == null || IV.Length <= 0) throw new ArgumentNullException("IV");
byte[] encrypted;
// Create an Aes object with the specified key and IV. using (Aes aesAlg = Aes.Create()) { aesAlg.Key = Key; aesAlg.IV = IV;
// Create a decrytor to perform the stream transform. ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for encryption. using (MemoryStream msEncrypt = new MemoryStream()) { using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)) { using (StreamWriter swEncrypt = new StreamWriter(csEncrypt)) { //Write all data to the stream. swEncrypt.Write(plainText); }
encrypted = msEncrypt.ToArray(); } } }
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// Return the encrypted bytes from the memory stream. return encrypted; }
static string DecryptStringFromBytes_Aes(byte[] cipherText, byte[] Key, byte[] IV) { // Check arguments. if (cipherText == null || cipherText.Length <= 0) throw new ArgumentNullException("cipherText"); if (Key == null || Key.Length <= 0) throw new ArgumentNullException("Key"); if (IV == null || IV.Length <= 0) throw new ArgumentNullException("IV");
// Declare the string used to hold the decrypted text. string plaintext = null;
// Create an Aes object with the specified key and IV. using (Aes aesAlg = Aes.Create()) { aesAlg.Key = Key; aesAlg.IV = IV;
// Create a decrytor to perform the stream transform. ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for decryption. using (MemoryStream msDecrypt = new MemoryStream(cipherText)) { using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read)) { using (StreamReader srDecrypt = new StreamReader(csDecrypt)) {
// Read the decrypted bytes from the decrypting stream // and place them in a string. plaintext = srDecrypt.ReadToEnd(); } } } }
return plaintext; } } }
This example is from MSDN.
It is a console demo application, showing how to encrypt a string by using the standard AES encryption, and how to decrypt it afterwards.
(AES = Advanced Encryption Standard, a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001 which is still the de-facto standard for symmetric encryption)
Notes:
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In a real encryption scenario, you need to choose a proper cipher mode (can be assigned to the Mode property by selecting a value from the CipherMode enumeration). Never use the CipherMode.ECB (electronic codebook mode), since this procuces a weak cypher stream
To create a good (and not a weak) Key, either use a cryptographic random generator or use the example above (Create a Key from a Password). The recommended KeySize is 256 bit. Supported key sizes are available via the LegalKeySizes property.
To initialize the initialization vector IV, you can use a SALT as shown in the example above (Random SALT)
Supported block sizes are available via the SupportedBlockSizes property, the block size can be assigned via the BlockSize property
Usage: see Main() method. Section 49.4: Create a Key from a Password / Random SALT (in C#)
using System; using System.Security.Cryptography; using System.Text;
public class PasswordDerivedBytesExample { public static void Main(String[] args) { // Get a password from the user. Console.WriteLine("Enter a password to produce a key:");
byte[] pwd = Encoding.Unicode.GetBytes(Console.ReadLine());
byte[] salt = CreateRandomSalt(7);
// Create a TripleDESCryptoServiceProvider object. TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();
try { Console.WriteLine("Creating a key with PasswordDeriveBytes…");
// Create a PasswordDeriveBytes object and then create // a TripleDES key from the password and salt. PasswordDeriveBytes pdb = new PasswordDeriveBytes(pwd, salt);
// Create the key and set it to the Key property // of the TripleDESCryptoServiceProvider object. tdes.Key = pdb.CryptDeriveKey("TripleDES", "SHA1", 192, tdes.IV);
Console.WriteLine("Operation complete."); } catch (Exception e) { Console.WriteLine(e.Message); } finally { // Clear the buffers ClearBytes(pwd); ClearBytes(salt);
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// Clear the key. tdes.Clear(); }
Console.ReadLine(); }
#region Helper methods
///

/// Generates a random salt value of the specified length. ///

public static byte[] CreateRandomSalt(int length) { // Create a buffer byte[] randBytes;
if (length >= 1) { randBytes = new byte[length]; } else { randBytes = new byte[1]; }
// Create a new RNGCryptoServiceProvider. RNGCryptoServiceProvider rand = new RNGCryptoServiceProvider();
// Fill the buffer with random bytes. rand.GetBytes(randBytes);
// return the bytes. return randBytes; }
///

/// Clear the bytes in a buffer so they can’t later be read from memory. ///

public static void ClearBytes(byte[] buffer) { // Check arguments. if (buffer == null) { throw new ArgumentNullException(“buffer”); }
// Set each byte in the buffer to 0. for (int x = 0; x errors.AppendLine(e.Data); process.Start(); process.BeginErrorReadLine(); process.WaitForExit();
if (errors.Length > 0) // something went wrong System.Console.Error.WriteLine($”Child process error: rn {errors}”);
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Chapter 53: Upload file and POST data to webserver Section 53.1: Upload file with WebRequest
To send a file and form data in single request, content should have multipart/form-data type.
using System; using System.Collections.Generic; using System.IO; using System.Net; using System.Threading.Tasks;
public async Task UploadFile(string url, string filename, Dictionary postData) { var request = WebRequest.CreateHttp(url); var boundary = $”{Guid.NewGuid():N}”; // boundary will separate each parameter request.ContentType = $”multipart/form-data; {nameof(boundary)}={boundary}”; request.Method = “POST”;
using (var requestStream = request.GetRequestStream()) using (var writer = new StreamWriter(requestStream)) { foreach (var data in postData) await writer.WriteAsync( // put all POST data into request $”rn–{boundary}rnContent-Disposition: ” + $”form-data; name=”{data.Key}”rnrn{data.Value}”);
await writer.WriteAsync( // file header $”rn–{boundary}rnContent-Disposition: ” + $”form-data; name=”File”; filename=”{Path.GetFileName(filename)}”rn” + “Content-Type: application/octet-streamrnrn”);
await writer.FlushAsync(); using (var fileStream = File.OpenRead(filename)) await fileStream.CopyToAsync(requestStream);
await writer.WriteAsync($”rn–{boundary}–rn”); }
using (var response = (HttpWebResponse) await request.GetResponseAsync()) using (var responseStream = response.GetResponseStream()) { if (responseStream == null) return string.Empty; using (var reader = new StreamReader(responseStream)) return await reader.ReadToEndAsync(); } }
Usage: var response = await uploader.UploadFile(“”, “”, new Dictionary { {“Comment”, “test”}, {“Modified”, DateTime.Now }
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});
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Chapter 54: Networking Section 54.1: Basic TCP chat (TcpListener, TcpClient, NetworkStream)
using System; using System.IO; using System.Net; using System.Net.Sockets; using System.Text;
class TcpChat { static void Main(string[] args) { if(args.Length == 0) { Console.WriteLine(“Basic TCP chat”); Console.WriteLine(); Console.WriteLine(“Usage:”); Console.WriteLine(“tcpchat server “); Console.WriteLine(“tcpchat client “); return; }
try { Run(args); } catch(IOException) { Console.WriteLine(“— Connection lost”); } catch(SocketException ex) { Console.WriteLine(“— Can’t connect: ” + ex.Message); } } static void Run(string[] args) { TcpClient client; NetworkStream stream; byte[] buffer = new byte[256]; var encoding = Encoding.ASCII;
if(args[0].StartsWith(“s”, StringComparison.InvariantCultureIgnoreCase)) { var port = int.Parse(args[1]); var listener = new TcpListener(IPAddress.Any, port); listener.Start(); Console.WriteLine(“— Waiting for a connection…”); client = listener.AcceptTcpClient(); } else { var hostName = args[1]; var port = int.Parse(args[2]); client = new TcpClient(); client.Connect(hostName, port);
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}
stream = client.GetStream(); Console.WriteLine(“— Connected. Start typing! (exit with Ctrl-C)”);
while(true) { if(Console.KeyAvailable) { var lineToSend = Console.ReadLine(); var bytesToSend = encoding.GetBytes(lineToSend + “rn”); stream.Write(bytesToSend, 0, bytesToSend.Length); stream.Flush(); }
if (stream.DataAvailable) { var receivedBytesCount = stream.Read(buffer, 0, buffer.Length); var receivedString = encoding.GetString(buffer, 0, receivedBytesCount); Console.Write(receivedString); } } } }
Section 54.2: Basic SNTP client (UdpClient)
See RFC 2030 for details on the SNTP protocol.
using System; using System.Globalization; using System.Linq; using System.Net; using System.Net.Sockets;
class SntpClient { const int SntpPort = 123; static DateTime BaseDate = new DateTime(1900, 1, 1);
static void Main(string[] args) { if(args.Length == 0) { Console.WriteLine(“Simple SNTP client”); Console.WriteLine(); Console.WriteLine(“Usage: sntpclient []”); Console.WriteLine(); Console.WriteLine(“: a number between -12 and 12 as hours from UTC”); Console.WriteLine(“(append .5 for an extra half an hour)”); return; }
double localTimeZoneInHours = 0; if(args.Length > 1) localTimeZoneInHours = double.Parse(args[1], CultureInfo.InvariantCulture);
var udpClient = new UdpClient(); udpClient.Client.ReceiveTimeout = 5000;
var sntpRequest = new byte[48]; sntpRequest[0] = 0x23; //LI=0 (no warning), VN=4, Mode=3 (client)
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udpClient.Send( dgram: sntpRequest, bytes: sntpRequest.Length, hostname: args[0], port: SntpPort);
byte[] sntpResponse; try { IPEndPoint remoteEndpoint = null; sntpResponse = udpClient.Receive(ref remoteEndpoint); } catch(SocketException) { Console.WriteLine(“*** No response received from the server”); return; }
uint numberOfSeconds; if(BitConverter.IsLittleEndian) numberOfSeconds = BitConverter.ToUInt32( sntpResponse.Skip(40).Take(4).Reverse().ToArray() ,0); else numberOfSeconds = BitConverter.ToUInt32(sntpResponse, 40); var date = BaseDate.AddSeconds(numberOfSeconds).AddHours(localTimeZoneInHours);
Console.WriteLine( $”Current date in server: {date:yyyy-MM-dd HH:mm:ss} UTC{localTimeZoneInHours:+0.#;-0.#;.}”); } }
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Chapter 55: HTTP servers Section 55.1: Basic read-only HTTP file server (ASP.NET Core)
1 – Create an empty folder, it will contain the files created in the next steps.
2 – Create a file named project.json with the following content (adjust the port number and rootDirectory as appropriate):
{ “dependencies”: { “Microsoft.AspNet.Server.Kestrel”: “1.0.0-rc1-final”, “Microsoft.AspNet.StaticFiles”: “1.0.0-rc1-final” },
“commands”: { “web”: “Microsoft.AspNet.Server.Kestrel –server.urls http://localhost:60000” },
“frameworks”: { “dnxcore50”: { } },
“fileServer”: { “rootDirectory”: “c:\users\username\Documents” } }
3 – Create a file named Startup.cs with the following code:
using System; using Microsoft.AspNet.Builder; using Microsoft.AspNet.FileProviders; using Microsoft.AspNet.Hosting; using Microsoft.AspNet.StaticFiles; using Microsoft.Extensions.Configuration;
public class Startup { public void Configure(IApplicationBuilder app) { var builder = new ConfigurationBuilder(); builder.AddJsonFile(“project.json”); var config = builder.Build(); var rootDirectory = config[“fileServer:rootDirectory”]; Console.WriteLine(“File server root directory: ” + rootDirectory);
var fileProvider = new PhysicalFileProvider(rootDirectory);
var options = new StaticFileOptions(); options.ServeUnknownFileTypes = true; options.FileProvider = fileProvider; options.OnPrepareResponse = context => { context.Context.Response.ContentType = “application/octet-stream”; context.Context.Response.Headers.Add( “Content-Disposition”, $”Attachment; filename=”{context.File.Name}””); };
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app.UseStaticFiles(options); } }
4 – Open a command prompt, navigate to the folder and execute:
dnvm use 1.0.0-rc1-final -r coreclr -p dnu restore
Note: These commands need to be run only once. Use dnvm list to check the actual number of the latest installed version of the core CLR.
5 – Start the server with: dnx web. Files can now be requested at http://localhost:60000/path/to/file.ext.
For simplicity, filenames are assumed to be all ASCII (for the filename part in the Content-Disposition header) and file access errors are not handled.
Section 55.2: Basic read-only HTTP file server (HttpListener) Notes:
This example must be run in administrative mode.
Only one simultaneous client is supported.
For simplicity, filenames are assumed to be all ASCII (for the filename part in the Content-Disposition header) and file access errors are not handled.
using System; using System.IO; using System.Net;
class HttpFileServer { private static HttpListenerResponse response; private static HttpListener listener; private static string baseFilesystemPath;
static void Main(string[] args) { if (!HttpListener.IsSupported) { Console.WriteLine( “*** HttpListener requires at least Windows XP SP2 or Windows Server 2003.”); return; }
if(args.Length < 2) { Console.WriteLine("Basic read-only HTTP file server"); Console.WriteLine(); Console.WriteLine("Usage: httpfileserver “); Console.WriteLine(“Request format: http://url:port/path/to/file.ext”); return; }
baseFilesystemPath = Path.GetFullPath(args[0]); var port = int.Parse(args[1]);
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listener = new HttpListener(); listener.Prefixes.Add(“http://*:” + port + “/”); listener.Start();
Console.WriteLine(“— Server stated, base path is: ” + baseFilesystemPath); Console.WriteLine(“— Listening, exit with Ctrl-C”); try { ServerLoop(); } catch(Exception ex) { Console.WriteLine(ex); if(response != null) { SendErrorResponse(500, “Internal server error”); } } }
static void ServerLoop() { while(true) { var context = listener.GetContext();
var request = context.Request; response = context.Response; var fileName = request.RawUrl.Substring(1); Console.WriteLine( “— Got {0} request for: {1}”, request.HttpMethod, fileName);
if (request.HttpMethod.ToUpper() != “GET”) { SendErrorResponse(405, “Method must be GET”); continue; }
var fullFilePath = Path.Combine(baseFilesystemPath, fileName); if(!File.Exists(fullFilePath)) { SendErrorResponse(404, “File not found”); continue; }
Console.Write(” Sending file…”); using (var fileStream = File.OpenRead(fullFilePath)) { response.ContentType = “application/octet-stream”; response.ContentLength64 = (new FileInfo(fullFilePath)).Length; response.AddHeader( “Content-Disposition”, “Attachment; filename=”” + Path.GetFileName(fullFilePath) + “””); fileStream.CopyTo(response.OutputStream); }
response.OutputStream.Close(); response = null; Console.WriteLine(” Ok!”); } }
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static void SendErrorResponse(int statusCode, string statusResponse) { response.ContentLength64 = 0; response.StatusCode = statusCode; response.StatusDescription = statusResponse; response.OutputStream.Close(); Console.WriteLine(“*** Sent error: {0} {1}”, statusCode, statusResponse); } }
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Chapter 56: HTTP clients Section 56.1: Reading GET response as string using System.Net.HttpClient
HttpClient is available through NuGet: Microsoft HTTP Client Libraries.
string requestUri = “http://www.example.com”; string responseData;
using (var client = new HttpClient()) { using(var response = client.GetAsync(requestUri).Result) { response.EnsureSuccessStatusCode(); responseData = response.Content.ReadAsStringAsync().Result; } }
Section 56.2: Basic HTTP downloader using System.Net.Http.HttpClient
using System; using System.IO; using System.Linq; using System.Net.Http; using System.Threading.Tasks;
class HttpGet { private static async Task DownloadAsync(string fromUrl, string toFile) { using (var fileStream = File.OpenWrite(toFile)) { using (var httpClient = new HttpClient()) { Console.WriteLine(“Connecting…”); using (var networkStream = await httpClient.GetStreamAsync(fromUrl)) { Console.WriteLine(“Downloading…”); await networkStream.CopyToAsync(fileStream); await fileStream.FlushAsync(); } } } }
static void Main(string[] args) { try { Run(args).Wait(); } catch (Exception ex) { if (ex is AggregateException) ex = ((AggregateException)ex).Flatten().InnerExceptions.First();
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Console.WriteLine(“— Error: ” + (ex.InnerException?.Message ?? ex.Message)); } } static async Task Run(string[] args) { if (args.Length < 2) { Console.WriteLine("Basic HTTP downloader"); Console.WriteLine(); Console.WriteLine("Usage: httpget [] “); return; }
await DownloadAsync(fromUrl: args[0], toFile: args[1]);
Console.WriteLine(“Done!”); } }
Section 56.3: Reading GET response as string using System.Net.HttpWebRequest
string requestUri = “http://www.example.com”; string responseData;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(parameters.Uri); WebResponse response = request.GetResponse();
using (StreamReader responseReader = new StreamReader(response.GetResponseStream())) { responseData = responseReader.ReadToEnd(); }
Section 56.4: Reading GET response as string using System.Net.WebClient
string requestUri = “http://www.example.com”; string responseData;
using (var client = new WebClient()) { responseData = client.DownloadString(requestUri); }
Section 56.5: Sending a POST request with a string payload using System.Net.HttpWebRequest
string requestUri = “http://www.example.com”; string requestBodyString = “Request body string.”; string contentType = “text/plain”; string requestMethod = “POST”;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(requestUri) { Method = requestMethod, ContentType = contentType, };
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byte[] bytes = Encoding.UTF8.GetBytes(requestBodyString); Stream stream = request.GetRequestStream(); stream.Write(bytes, 0, bytes.Length); stream.Close();
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Section 56.6: Sending a POST request with a string payload using System.Net.WebClient
string requestUri = “http://www.example.com”; string requestBodyString = “Request body string.”; string contentType = “text/plain”; string requestMethod = “POST”; byte[] responseBody; byte[] requestBodyBytes = Encoding.UTF8.GetBytes(requestBodyString);
using (var client = new WebClient()) { client.Headers[HttpRequestHeader.ContentType] = contentType; responseBody = client.UploadData(requestUri, requestMethod, requestBodyBytes); }
Section 56.7: Sending a POST request with a string payload using System.Net.HttpClient
HttpClient is available through NuGet: Microsoft HTTP Client Libraries.
string requestUri = “http://www.example.com”; string requestBodyString = “Request body string.”; string contentType = “text/plain”; string requestMethod = “POST”;
var request = new HttpRequestMessage { RequestUri = requestUri, Method = requestMethod, };
byte[] requestBodyBytes = Encoding.UTF8.GetBytes(requestBodyString); request.Content = new ByteArrayContent(requestBodyBytes);
request.Content.Headers.ContentType = new MediaTypeHeaderValue(contentType);
HttpResponseMessage result = client.SendAsync(request).Result; result.EnsureSuccessStatusCode();
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Chapter 57: Serial Ports Section 57.1: Basic operation
var serialPort = new SerialPort(“COM1”, 9600, Parity.Even, 8, StopBits.One); serialPort.Open(); serialPort.WriteLine(“Test data”); string response = serialPort.ReadLine(); Console.WriteLine(response); serialPort.Close();
Section 57.2: List available port names
string[] portNames = SerialPort.GetPortNames();
Section 57.3: Asynchronous read
void SetupAsyncRead(SerialPort serialPort) { serialPort.DataReceived += (sender, e) => { byte[] buffer = new byte[4096]; switch (e.EventType) { case SerialData.Chars: var port = (SerialPort)sender; int bytesToRead = port.BytesToRead; if (bytesToRead > buffer.Length) Array.Resize(ref buffer, bytesToRead); int bytesRead = port.Read(buffer, 0, bytesToRead); // Process the read buffer here // … break; case SerialData.Eof: // Terminate the service here // … break; } };
Section 57.4: Synchronous text echo service
using System.IO.Ports;
namespace TextEchoService { class Program { static void Main(string[] args) { var serialPort = new SerialPort(“COM1”, 9600, Parity.Even, 8, StopBits.One); serialPort.Open(); string message = “”; while (message != “quit”) { message = serialPort.ReadLine(); serialPort.WriteLine(message); }
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serialPort.Close(); } } }
Section 57.5: Asynchronous message receiver
using System; using System.Collections.Generic; using System.IO.Ports; using System.Text; using System.Threading;
namespace AsyncReceiver { class Program { const byte STX = 0x02; const byte ETX = 0x03; const byte ACK = 0x06; const byte NAK = 0x15; static ManualResetEvent terminateService = new ManualResetEvent(false); static readonly object eventLock = new object(); static List unprocessedBuffer = null;
static void Main(string[] args) { try { var serialPort = new SerialPort(“COM11”, 9600, Parity.Even, 8, StopBits.One); serialPort.DataReceived += DataReceivedHandler; serialPort.ErrorReceived += ErrorReceivedHandler; serialPort.Open(); terminateService.WaitOne(); serialPort.Close(); } catch (Exception e) { Console.WriteLine(“Exception occurred: {0}”, e.Message); } Console.ReadKey(); }
static void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e) { lock (eventLock) { byte[] buffer = new byte[4096]; switch (e.EventType) { case SerialData.Chars: var port = (SerialPort)sender; int bytesToRead = port.BytesToRead; if (bytesToRead > buffer.Length) Array.Resize(ref buffer, bytesToRead); int bytesRead = port.Read(buffer, 0, bytesToRead); ProcessBuffer(buffer, bytesRead); break; case SerialData.Eof: terminateService.Set(); break;
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} } } static void ErrorReceivedHandler(object sender, SerialErrorReceivedEventArgs e) { lock (eventLock) if (e.EventType == SerialError.TXFull) { Console.WriteLine(“Error: TXFull. Can’t handle this!”); terminateService.Set(); } else { Console.WriteLine(“Error: {0}. Resetting everything”, e.EventType); var port = (SerialPort)sender; port.DiscardInBuffer(); port.DiscardOutBuffer(); unprocessedBuffer = null; port.Write(new byte[] { NAK }, 0, 1); } }
static void ProcessBuffer(byte[] buffer, int length) { List message = unprocessedBuffer; for (int i = 0; i < length; i++) if (buffer[i] == ETX) { if (message != null) { Console.WriteLine("MessageReceived: {0}", Encoding.ASCII.GetString(message.ToArray())); message = null; } } else if (buffer[i] == STX) message = null; else if (message != null) message.Add(buffer[i]); unprocessedBuffer = message; } } }
This program waits for messages enclosed in STX and ETX bytes and outputs the text coming between them. Everything else is discarded. On write buffer overflow it stops. On other errors it reset input and output buffers and waits for further messages.
The code illustrates:
Asynchronous serial port reading (see SerialPort.DataReceived usage). Serial port error processing (see SerialPort.ErrorReceived usage). Non-text message-based protocol implementation. Partial message reading.
The SerialPort.DataReceived event may happen earlier than entire message (up to ETX) comes. The entire message may also not be available in the input buffer (SerialPort.Read(…, …, port.BytesToRead) reads only a part of the message). In this case we stash the received part (unprocessedBuffer) and carry on waiting for further data.
Dealing with several messages coming in one go.
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The SerialPort.DataReceived event may happen only after several messages have been sent by the other end.
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Appendix A: Acronym Glossary Section A.1: .Net Related Acronyms
Please note that some terms like JIT and GC are generic enough to apply to many programming language environments and runtimes.
CLR: Common Language Runtime IL: Intermediate Language EE: Execution Engine JIT: Just-in-time compiler GC: Garbage Collector OOM: Out of memory STA: Single-threaded apartment MTA: Multi-threaded apartment
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Credits
Thank you greatly to all the people from Stack Overflow Documentation who helped provide this content,
more changes can be sent to web@petercv.com for new content to be published or updated
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Chapters 42 and 47 Chapter 8 Chapters 1, 2, 4 and 18 Chapter 25 Chapters 12, 14 and 47 Chapters 16 and 35 Chapters 10, 52 and 53 Chapter 49 Chapter 8 Chapter 47 Chapters 5 and 42 Chapter 1 Chapter 25 Chapter 28 Chapter 32 Chapter 28 Chapter 34 Chapter 47 Chapter 19 Chapter 28 Chapter 1 Chapter 46 Chapter 51 Chapter 47 Chapter 48 Chapter 39 Chapter 8 Chapter 45 Chapters 4 and 10 Chapter 8 Chapter 8 Chapter 15 Chapter 8 Chapters 8, 17, 28, 47 and 56 Chapters 1 and 25 Chapter 4 Chapter 47 Chapter 35 Chapter 18 Chapters 30 and 49 Chapter 15 Chapters 31 and 33 Chapters 27 and 57 Chapter 8 Chapter 9 Chapter 25 Chapters 12 and 45
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Chapter 8 Chapter 8 Chapter 32 Chapters 4 and 5 Chapter 17 Chapter 48 Chapter 37 Chapters 3 and 8 Chapters 4, 11 and 34 Chapter 22 Chapters 43 and 44 Chapter 8 Chapter 5 Chapter 4 Chapter 25 Chapter 4 Chapter 7 Chapter 38 Chapter 4 Chapter 25 Chapter 16 Chapters 38, 42 and 43 Chapter 49 Chapter 42 Chapter 8 Chapter 10 Chapter 11 Chapter 8 Chapters 8 and 20 Chapter 3 Chapter 1 Chapters 8, 42, 54, 55 and 56 Chapter 36 Chapter 47 Chapter 49 Chapter 10 Chapter 23 Chapter 9 Chapter 32 Chapter 47 Chapter 50 Chapters 1 and 8 Chapter 5 Chapters 10 and 28 Chapter 42 Chapter 49 Chapter 15 Chapter 1 Chapter 13 Chapter 8 Chapter 39 Chapter 24 Chapter 8
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Chapter 40 Chapter 11 Chapter 8 Chapter 38 Chapter 23 Chapter 48 Chapter 48 Chapter 28 Chapter 42 Chapters 2 and 42 Chapter 32 Chapter 21 Chapter 4 Chapter 1 Chapter 4 Chapter 17 Chapter 8 Chapter 8 Chapter 8 Chapters 26 and 29 Chapter 1 Chapter 8 Chapter 8 Chapter 10 Chapters 37 and 47 Chapter 30 Chapter 1 Chapter 11 Chapter 58 Chapters 6 and 15 Chapter 4
Chapter 37
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