Create a custom means of managing the event invocation list
/*
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();
}
}
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