What do you mean by "extension methods" in C#?

Can anyone else explain this开发者_运维百科, (beginners approach). Thanks..

Extension Methods are just static methods in static classes that behaves like they were defined in other class.
In the first parameter before the type goes the keyword this wich indicates that is an extension method.

Example:

public static class Extensions
{
    public static object ExtensionMethodForStrings( this string s, object otherParameter)
    {
        //....
        return //whatever you want to return or not
    }
}

This is an extension method on System.String that takes two parameters: - string s : This is the instance variable - object otherParameter: You can have as many as you want including none

You can call this method in two ways:

Static way:

string s = "Your string";
object o = new object(); // or whatever you want
object result = Extensions.ExtensionMethodForStrings(s,o);

Extension Method way

string s = "Your string";
object o = new object(); // or whatever you want
object result = s.ExtensionMethodForStrings(o);

In the second case it works as if the type string has an instance method called ExtensionMethodForStrings. Actually for the compiler the are equivalent.

Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are a special kind of static method, but they are called as if they were instance methods on the extended type. For client code written in C# and Visual Basic, there is no apparent difference between calling an extension method and the methods that are actually defined in a type.

The C# article on Extension Methods.

An extension method is a static method in a static class whose first parameter is preceded by the keyword this.

The C# compiler has some syntactic sugar that can convert a call of x.Foo(bar) to SomeExtension.Foo(x, bar). This is used extensively by LINQ (Take, Skip, Where, Select, etc.) but you can also write your own extension methods if you wish.

This question includes lots of examples of useful extension methods:

• What are your favorite extension methods for C#? (codeplex.com/extensionoverflow)

An extension method is a method that behaves (somewhat) like it is a member of a class, but it is not a member of that class. It can be called on members of that class, but has no reference to the internals of the class.

Extension methods are static methods, and must be members of a static class.

public static class StringExtensions
{
    public static string HtmlEncode(this string dataString)
    {
        return HttpServerUtility.HtmlEncode(dataString);
    }
}

The keyword "this" prior to the first parameter type identifies this as an extension method, and the class it extends.

It would be used this way:

string foo = "bar";
string myOutput = foo.HtmlEncode();