/*
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(); } } [/csharp]