passing this as parameter in static method

Question

I'm having some trouble with some code in Visual C# for Windows Phone The trouble is not that it does not work, because it does, but I don't understand how =P Within a static class, a static method is created, which gives itself as a parameter:

public static void MethodONe( this Timeline animation )
{
    //this class does not extend the TimeLine class, and is not connected to it in any                   
    //such way.
    animation.MethodTwo( );
}

public static void MethodTwo( this Timeline animation )
{
    someCode( );
}

How is this parameterpassing called, and what does it do, exactly?

Answer 1

This is a so called extention method to the Timeline object. It adds functionallity without modifying the class itself.

http://msdn.microsoft.com/en-us/library/bb383977.aspx

And in your case the animation parameter is the Timeline object (which is calling the function):

var timeLine = new Timeline();
timeLine.MethodTwo();

So the timeLine object will be passed as the animation parameter into the function. There's a nice article on wikipedia which explains it futher in detail:

http://en.wikipedia.org/wiki/Extension_method