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-rw-r--r--csharp.html.markdown262
1 files changed, 205 insertions, 57 deletions
diff --git a/csharp.html.markdown b/csharp.html.markdown
index 47dd9683..dfdd98de 100644
--- a/csharp.html.markdown
+++ b/csharp.html.markdown
@@ -5,6 +5,9 @@ contributors:
- ["Max Yankov", "https://github.com/golergka"]
- ["Melvyn Laïly", "http://x2a.yt"]
- ["Shaun McCarthy", "http://www.shaunmccarthy.com"]
+ - ["Wouter Van Schandevijl", "http://github.com/laoujin"]
+ - ["Jo Pearce", "http://github.com/jdpearce"]
+ - ["Chris Zimmerman", "https://github.com/chriszimmerman"]
filename: LearnCSharp.cs
---
@@ -18,29 +21,36 @@ C# is an elegant and type-safe object-oriented language that enables developers
Multi-line comments look like this
*/
/// <summary>
-/// This is an XML documentation comment
+/// This is an XML documentation comment which can be used to generate external
+/// documentation or provide context help within an IDE
/// </summary>
+//public void MethodOrClassOrOtherWithParsableHelp() {}
-// Specify namespaces application will be using
+// Specify the namespaces this source code will be using
+// The namespaces below are all part of the standard .NET Framework Class Libary
using System;
using System.Collections.Generic;
-using System.Data.Entity;
using System.Dynamic;
using System.Linq;
-using System.Linq.Expressions;
using System.Net;
using System.Threading.Tasks;
using System.IO;
-// defines scope to organize code into "packages"
-namespace Learning
+// But this one is not:
+using System.Data.Entity;
+// In order to be able to use it, you need to add a dll reference
+// This can be done with the NuGet package manager: `Install-Package EntityFramework`
+
+// Namespaces define scope to organize code into "packages" or "modules"
+// Using this code from another source file: using Learning.CSharp;
+namespace Learning.CSharp
{
// Each .cs file should at least contain a class with the same name as the file
// you're allowed to do otherwise, but shouldn't for sanity.
public class LearnCSharp
{
// BASIC SYNTAX - skip to INTERESTING FEATURES if you have used Java or C++ before
- public static void Syntax()
+ public static void Syntax()
{
// Use Console.WriteLine to print lines
Console.WriteLine("Hello World");
@@ -125,7 +135,7 @@ on a new line! ""Wow!"", the masses cried";
// Use const or read-only to make a variable immutable
// const values are calculated at compile time
- const int HOURS_I_WORK_PER_WEEK = 9001;
+ const int HoursWorkPerWeek = 9001;
///////////////////////////////////////////////////
// Data Structures
@@ -151,7 +161,7 @@ on a new line! ""Wow!"", the masses cried";
// List<datatype> <var name> = new List<datatype>();
List<int> intList = new List<int>();
List<string> stringList = new List<string>();
- List<int> z = new List<int> { 9000, 1000, 1337 }; // intialize
+ List<int> z = new List<int> { 9000, 1000, 1337 }; // initialize
// The <> are for generics - Check out the cool stuff section
// Lists don't default to a value;
@@ -228,7 +238,8 @@ on a new line! ""Wow!"", the masses cried";
// Ternary operators
// A simple if/else can be written as follows
// <condition> ? <true> : <false>
- string isTrue = (true) ? "True" : "False";
+ int toCompare = 17;
+ string isTrue = toCompare == 17 ? "True" : "False";
// While loop
int fooWhile = 0;
@@ -242,8 +253,15 @@ on a new line! ""Wow!"", the masses cried";
int fooDoWhile = 0;
do
{
- //Iterated 100 times, fooDoWhile 0->99
+ // Start iteration 100 times, fooDoWhile 0->99
+ if (false)
+ continue; // skip the current iteration
+
fooDoWhile++;
+
+ if (fooDoWhile == 50)
+ break; // breaks from the loop completely
+
} while (fooDoWhile < 100);
//for loop structure => for(<start_statement>; <conditional>; <step>)
@@ -301,7 +319,7 @@ on a new line! ""Wow!"", the masses cried";
// Converting data
// Convert String To Integer
- // this will throw an Exception on failure
+ // this will throw a FormatException on failure
int.Parse("123");//returns an integer version of "123"
// try parse will default to type default on failure
@@ -315,6 +333,11 @@ on a new line! ""Wow!"", the masses cried";
Convert.ToString(123);
// or
tryInt.ToString();
+
+ // Casting
+ // Cast decimal 15 to a int
+ // and then implicitly cast to long
+ long x = (int) 15M;
}
///////////////////////////////////////
@@ -350,11 +373,11 @@ on a new line! ""Wow!"", the masses cried";
//
// INTERESTING FEATURES
//
-
+
// DEFAULT METHOD SIGNATURES
public // Visibility
- static // Allows for direct call on class without object
+ static // Allows for direct call on class without object
int // Return Type,
MethodSignatures(
int maxCount, // First variable, expects an int
@@ -362,21 +385,26 @@ on a new line! ""Wow!"", the masses cried";
int another = 3,
params string[] otherParams // captures all other parameters passed to method
)
- {
+ {
return -1;
}
// Methods can have the same name, as long as the signature is unique
- public static void MethodSignatures(string maxCount)
+ // A method that differs only in return type is not unique
+ public static void MethodSignatures(
+ ref int maxCount, // Pass by reference
+ out int count)
{
+ //the argument passed in as 'count' will hold the value of 15 outside of this function
+ count = 15; // out param must be assigned before control leaves the method
}
// GENERICS
// The classes for TKey and TValue is specified by the user calling this function.
// This method emulates the SetDefault of Python
public static TValue SetDefault<TKey, TValue>(
- IDictionary<TKey, TValue> dictionary,
- TKey key,
+ IDictionary<TKey, TValue> dictionary,
+ TKey key,
TValue defaultItem)
{
TValue result;
@@ -385,7 +413,7 @@ on a new line! ""Wow!"", the masses cried";
return result;
}
- // You can narrow down the objects that are passed in
+ // You can narrow down the objects that are passed in
public static void IterateAndPrint<T>(T toPrint) where T: IEnumerable<int>
{
// We can iterate, since T is a IEnumerable
@@ -393,12 +421,52 @@ on a new line! ""Wow!"", the masses cried";
// Item is an int
Console.WriteLine(item.ToString());
}
+
+ // YIELD
+ // Usage of the "yield" keyword indicates that the method it appears in is an Iterator
+ // (this means you can use it in a foreach loop)
+ public static IEnumerable<int> YieldCounter(int limit = 10)
+ {
+ for (var i = 0; i < limit; i++)
+ yield return i;
+ }
+
+ // which you would call like this :
+ public static void PrintYieldCounterToConsole()
+ {
+ foreach (var counter in YieldCounter())
+ Console.WriteLine(counter);
+ }
+
+ // you can use more than one "yield return" in a method
+ public static IEnumerable<int> ManyYieldCounter()
+ {
+ yield return 0;
+ yield return 1;
+ yield return 2;
+ yield return 3;
+ }
+
+ // you can also use "yield break" to stop the Iterator
+ // this method would only return half of the values from 0 to limit.
+ public static IEnumerable<int> YieldCounterWithBreak(int limit = 10)
+ {
+ for (var i = 0; i < limit; i++)
+ {
+ if (i > limit/2) yield break;
+ yield return i;
+ }
+ }
public static void OtherInterestingFeatures()
{
// OPTIONAL PARAMETERS
MethodSignatures(3, 1, 3, "Some", "Extra", "Strings");
- MethodSignatures(3, another: 3); // explicity set a parameter, skipping optional ones
+ MethodSignatures(3, another: 3); // explicitly set a parameter, skipping optional ones
+
+ // BY REF AND OUT PARAMETERS
+ int maxCount = 0, count; // ref params must have value
+ MethodSignatures(ref maxCount, out count);
// EXTENSION METHODS
int i = 3;
@@ -414,6 +482,9 @@ on a new line! ""Wow!"", the masses cried";
// ?? is syntactic sugar for specifying default value (coalesce)
// in case variable is null
int notNullable = nullable ?? 0; // 0
+
+ // ?. is an operator for null-propagation - a shorthand way of checking for null
+ nullable?.Print(); // Use the Print() extension method if nullable isn't null
// IMPLICITLY TYPED VARIABLES - you can let the compiler work out what the type is:
var magic = "magic is a string, at compile time, so you still get type safety";
@@ -421,13 +492,13 @@ on a new line! ""Wow!"", the masses cried";
// GENERICS
//
- var phonebook = new Dictionary<string, string>() {
+ var phonebook = new Dictionary<string, string>() {
{"Sarah", "212 555 5555"} // Add some entries to the phone book
};
// Calling SETDEFAULT defined as a generic above
Console.WriteLine(SetDefault<string,string>(phonebook, "Shaun", "No Phone")); // No Phone
- // nb, you don't need to specify the TKey and TValue since they can be
+ // nb, you don't need to specify the TKey and TValue since they can be
// derived implicitly
Console.WriteLine(SetDefault(phonebook, "Sarah", "No Phone")); // 212 555 5555
@@ -435,28 +506,53 @@ on a new line! ""Wow!"", the masses cried";
Func<int, int> square = (x) => x * x; // Last T item is the return value
Console.WriteLine(square(3)); // 9
+ // ERROR HANDLING - coping with an uncertain world
+ try
+ {
+ var funBike = PennyFarthing.CreateWithGears(6);
+
+ // will no longer execute because CreateWithGears throws an exception
+ string some = "";
+ if (true) some = null;
+ some.ToLower(); // throws a NullReferenceException
+ }
+ catch (NotSupportedException)
+ {
+ Console.WriteLine("Not so much fun now!");
+ }
+ catch (Exception ex) // catch all other exceptions
+ {
+ throw new ApplicationException("It hit the fan", ex);
+ // throw; // A rethrow that preserves the callstack
+ }
+ // catch { } // catch-all without capturing the Exception
+ finally
+ {
+ // executes after try or catch
+ }
+
// DISPOSABLE RESOURCES MANAGEMENT - let you handle unmanaged resources easily.
// Most of objects that access unmanaged resources (file handle, device contexts, etc.)
- // implement the IDisposable interface. The using statement takes care of
+ // implement the IDisposable interface. The using statement takes care of
// cleaning those IDisposable objects for you.
using (StreamWriter writer = new StreamWriter("log.txt"))
{
writer.WriteLine("Nothing suspicious here");
// At the end of scope, resources will be released.
// Even if an exception is thrown.
- }
+ }
// PARALLEL FRAMEWORK
// http://blogs.msdn.com/b/csharpfaq/archive/2010/06/01/parallel-programming-in-net-framework-4-getting-started.aspx
- var websites = new string[] {
- "http://www.google.com", "http://www.reddit.com",
+ var websites = new string[] {
+ "http://www.google.com", "http://www.reddit.com",
"http://www.shaunmccarthy.com"
};
var responses = new Dictionary<string, string>();
-
+
// Will spin up separate threads for each request, and join on them
// before going to the next step!
- Parallel.ForEach(websites,
+ Parallel.ForEach(websites,
new ParallelOptions() {MaxDegreeOfParallelism = 3}, // max of 3 threads
website =>
{
@@ -480,7 +576,7 @@ on a new line! ""Wow!"", the masses cried";
(introduceTo) => string.Format("Hey {0}, this is {1}", student.FirstName, introduceTo));
Console.WriteLine(student.Introduce("Beth"));
- // IQUERYABLE<T> - almost all collections implement this, which gives you a lot of
+ // IQUERYABLE<T> - almost all collections implement this, which gives you a lot of
// very useful Map / Filter / Reduce style methods
var bikes = new List<Bicycle>();
bikes.Sort(); // Sorts the array
@@ -502,8 +598,8 @@ on a new line! ""Wow!"", the masses cried";
// ASPARALLEL
// And this is where things get wicked - combines linq and parallel operations
var threeWheelers = bikes.AsParallel().Where(b => b.Wheels == 3).Select(b => b.Name);
- // this will happen in parallel! Threads will automagically be spun up and the
- // results divvied amongst them! Amazing for large datasets when you have lots of
+ // this will happen in parallel! Threads will automagically be spun up and the
+ // results divvied amongst them! Amazing for large datasets when you have lots of
// cores
// LINQ - maps a store to IQueryable<T> objects, with delayed execution
@@ -521,9 +617,9 @@ on a new line! ""Wow!"", the masses cried";
.Select(b => b.Name); // still no query run
// Now the query runs, but opens a reader, so only populates are you iterate through
- foreach (string bike in query)
+ foreach (string bike in query)
Console.WriteLine(result);
-
+
}
@@ -556,7 +652,7 @@ on a new line! ""Wow!"", the masses cried";
{
return _cadence;
}
- set // set - define a method to set a proprety
+ set // set - define a method to set a property
{
_cadence = value; // Value is the value passed in to the setter
}
@@ -575,7 +671,7 @@ on a new line! ""Wow!"", the masses cried";
private set; // You can set modifiers on the get/set methods
}
- int _speed; // Everything is private by default: Only accessible from within this class.
+ int _speed; // Everything is private by default: Only accessible from within this class.
// can also use keyword private
public string Name { get; set; }
@@ -595,10 +691,26 @@ on a new line! ""Wow!"", the masses cried";
public BikeBrand Brand; // After declaring an enum type, we can declare the field of this type
+ // Decorate an enum with the FlagsAttribute to indicate that multiple values can be switched on
+ [Flags] // Any class derived from Attribute can be used to decorate types, methods, parameters etc
+ public enum BikeAccessories
+ {
+ None = 0,
+ Bell = 1,
+ MudGuards = 2, // need to set the values manually!
+ Racks = 4,
+ Lights = 8,
+ FullPackage = Bell | MudGuards | Racks | Lights
+ }
+
+ // Usage: aBike.Accessories.HasFlag(Bicycle.BikeAccessories.Bell)
+ // Before .NET 4: (aBike.Accessories & Bicycle.BikeAccessories.Bell) == Bicycle.BikeAccessories.Bell
+ public BikeAccessories Accessories { get; set; }
+
// Static members belong to the type itself rather then specific object.
// You can access them without a reference to any object:
// Console.WriteLine("Bicycles created: " + Bicycle.bicyclesCreated);
- static public int BicyclesCreated = 0;
+ public static int BicyclesCreated { get; set; }
// readonly values are set at run time
// they can only be assigned upon declaration or in a constructor
@@ -606,7 +718,7 @@ on a new line! ""Wow!"", the masses cried";
// Constructors are a way of creating classes
// This is a default constructor
- public Bicycle()
+ public Bicycle()
{
this.Gear = 1; // you can access members of the object with the keyword this
Cadence = 50; // but you don't always need it
@@ -618,13 +730,13 @@ on a new line! ""Wow!"", the masses cried";
// This is a specified constructor (it contains arguments)
public Bicycle(int startCadence, int startSpeed, int startGear,
- string name, bool hasCardsInSpokes, BikeBrand brand)
+ string name, bool hasCardsInSpokes, BikeBrand brand)
: base() // calls base first
{
- Gear = startGear;
+ Gear = startGear;
Cadence = startCadence;
_speed = startSpeed;
- Name = name;
+ Name = name;
_hasCardsInSpokes = hasCardsInSpokes;
Brand = brand;
}
@@ -680,9 +792,9 @@ on a new line! ""Wow!"", the masses cried";
// It's also possible to define custom Indexers on objects.
// All though this is not entirely useful in this example, you
- // could do bicycle[0] which yields "chris" to get the first passenger or
+ // could do bicycle[0] which returns "chris" to get the first passenger or
// bicycle[1] = "lisa" to set the passenger. (of this apparent quattrocycle)
- private string[] passengers = { "chris", "phil", "darren", "regina" }
+ private string[] passengers = { "chris", "phil", "darren", "regina" };
public string this[int i]
{
@@ -691,7 +803,7 @@ on a new line! ""Wow!"", the masses cried";
}
set {
- return passengers[i] = value;
+ passengers[i] = value;
}
}
@@ -737,10 +849,17 @@ on a new line! ""Wow!"", the masses cried";
}
set
{
- throw new ArgumentException("You can't change gears on a PennyFarthing");
+ throw new InvalidOperationException("You can't change gears on a PennyFarthing");
}
}
+ public static PennyFarthing CreateWithGears(int gears)
+ {
+ var penny = new PennyFarthing(1, 1);
+ penny.Gear = gears; // Oops, can't do this!
+ return penny;
+ }
+
public override string Info()
{
string result = "PennyFarthing bicycle ";
@@ -760,7 +879,8 @@ on a new line! ""Wow!"", the masses cried";
bool Broken { get; } // interfaces can contain properties as well as methods & events
}
- // Class can inherit only one other class, but can implement any amount of interfaces
+ // Class can inherit only one other class, but can implement any amount of interfaces, however
+ // the base class name must be the first in the list and all interfaces follow
class MountainBike : Bicycle, IJumpable, IBreakable
{
int damage = 0;
@@ -780,11 +900,11 @@ on a new line! ""Wow!"", the masses cried";
}
/// <summary>
- /// Used to connect to DB for LinqToSql example.
+ /// Used to connect to DB for LinqToSql example.
/// EntityFramework Code First is awesome (similar to Ruby's ActiveRecord, but bidirectional)
/// http://msdn.microsoft.com/en-us/data/jj193542.aspx
/// </summary>
- public class BikeRepository : DbSet
+ public class BikeRepository : DbContext
{
public BikeRepository()
: base()
@@ -793,18 +913,49 @@ on a new line! ""Wow!"", the masses cried";
public DbSet<Bicycle> Bikes { get; set; }
}
+
+ // Classes can be split across multiple .cs files
+ // A1.cs
+ public partial class A
+ {
+ public static void A1()
+ {
+ Console.WriteLine("Method A1 in class A");
+ }
+ }
+
+ // A2.cs
+ public partial class A
+ {
+ public static void A2()
+ {
+ Console.WriteLine("Method A2 in class A");
+ }
+ }
+
+ // Program using the partial class "A"
+ public class Program
+ {
+ static void Main()
+ {
+ A.A1();
+ A.A2();
+ }
+ }
} // End Namespace
```
## Topics Not Covered
- * Flags
* Attributes
- * Static properties
- * Exceptions, Abstraction
- * ASP.NET (Web Forms/MVC/WebMatrix)
- * Winforms
- * Windows Presentation Foundation (WPF)
+ * async/await, pragma directives
+ * Web Development
+ * ASP.NET MVC & WebApi (new)
+ * ASP.NET Web Forms (old)
+ * WebMatrix (tool)
+ * Desktop Development
+ * Windows Presentation Foundation (WPF) (new)
+ * Winforms (old)
## Further Reading
@@ -817,7 +968,4 @@ on a new line! ""Wow!"", the masses cried";
* [ASP.NET Web Matrix Tutorials](http://www.asp.net/web-pages/tutorials)
* [ASP.NET Web Forms Tutorials](http://www.asp.net/web-forms/tutorials)
* [Windows Forms Programming in C#](http://www.amazon.com/Windows-Forms-Programming-Chris-Sells/dp/0321116208)
-
-
-
-[C# Coding Conventions](http://msdn.microsoft.com/en-us/library/vstudio/ff926074.aspx)
+ * [C# Coding Conventions](http://msdn.microsoft.com/en-us/library/vstudio/ff926074.aspx)