Create a custom means of managing the event invocation list : delegate Event : Language Basics C# Source Code

    

/*
C#: The Complete Reference 
by Herbert Schildt 

Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/


// Create a custom means of managing the event invocation list. 
   
using System;  
  
// Declare a delegate for an event.   
delegate void MyEventHandler();  
  
// Declare an event class that holds up to 3 events. 
class MyEvent {  
  MyEventHandler[] evnt = new MyEventHandler[3]; 
 
  public event MyEventHandler SomeEvent { 
    // Add an event to the list. 
    add { 
      int i; 
 
      for(i=0; i < 3; i++) 
        if(evnt[i] == null) { 
          evnt[i] = value;  
          break; 
        } 
      if (i == 3) Console.WriteLine("Event list full."); 
    } 
 
    // Remove an event from the list. 
    remove { 
      int i; 
 
      for(i=0; i < 3; i++) 
        if(evnt[i] == value) { 
          evnt[i] = null; 
          break; 
        } 
      if (i == 3) Console.WriteLine("Event handler not found."); 
    } 
  }  
  
  // This is called to fire the events.  
  public void OnSomeEvent() {  
      for(int i=0; i < 3; i++) 
        if(evnt[i] != null) evnt[i]();  
  }  
 
}  
  
// Create some classes that use MyEventHandler. 
class W { 
  public void Whandler() {  
    Console.WriteLine("Event received by W object");  
  }  
}  
  
class X { 
  public void Xhandler() {  
    Console.WriteLine("Event received by X object");  
  }  
}  
  
class Y {  
  public void Yhandler() {  
    Console.WriteLine("Event received by Y object");  
  }  
}  
  
class Z {  
  public void Zhandler() {  
    Console.WriteLine("Event received by Z object");  
  }  
}  
  
public class EventDemo4 {  
  public static void Main() {   
    MyEvent evt = new MyEvent();  
    W wOb = new W();  
    X xOb = new X();  
    Y yOb = new Y();  
    Z zOb = new Z(); 
 
    // Add handlers to the event list. 
    Console.WriteLine("Adding events."); 
    evt.SomeEvent += new MyEventHandler(wOb.Whandler);  
    evt.SomeEvent += new MyEventHandler(xOb.Xhandler);  
    evt.SomeEvent += new MyEventHandler(yOb.Yhandler);  
 
    // Can't store this one -- full. 
    evt.SomeEvent += new MyEventHandler(zOb.Zhandler);  
    Console.WriteLine(); 
  
    // Fire the events.  
    evt.OnSomeEvent();  
    Console.WriteLine();  
  
    // Remove a handler. 
    Console.WriteLine("Remove xOb.Xhandler."); 
    evt.SomeEvent -= new MyEventHandler(xOb.Xhandler);  
    evt.OnSomeEvent();  
 
    Console.WriteLine(); 
 
    // Try to remove it again. 
    Console.WriteLine("Try to remove xOb.Xhandler again."); 
    evt.SomeEvent -= new MyEventHandler(xOb.Xhandler);  
    evt.OnSomeEvent();  
 
    Console.WriteLine(); 
 
    // Now, add Zhandler. 
    Console.WriteLine("Add zOb.Zhandler."); 
    evt.SomeEvent += new MyEventHandler(zOb.Zhandler); 
    evt.OnSomeEvent();  
 
  }  
}