Event Handling in C#, Free online C# Programming Tutorial...

Events are used extensively in GUI programming. An event, in C#, is a special kind of delegate that facilitates event-driven programming. Events are class members, which we cannot call outside of the class regardless of its access specifier. In other words, an event declared as public in a class allows other classes to use += operator to add methods to the event. We can also use -= operator to remove methods form a delegate or an event. However, firing the event (i.e. invoking the delegate) is only allowed in the class containing the event.

Now consider the following example:

delegate void SimpleButtonClickHandler();
class MyButton
{ 
   public event SimpleButtonClickHandler MyButtonClicked; 
   public void SimulateButtonClick() 
   { 
      if (MyButtonClicked != null) 
      { 
         ButtonClicked(); 
      } 
   } 
   ...
}

A method in another class can then subscribe to the event by adding one of its methods to the event delegate:

MyButton b = new MyButton();
b.ButtonClicked += MyClickHandler;

Note that despite the fact that the event is declared as public, it cannot be directly fired from anywhere except in the class containing the event.

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