C # Event Accessors

We can control the behavior of the event operator + =, by defining an event accessor for an event

There are two accessors: Add and remove

The accessor that declares the event looks almost as if it were declaring an attribute

The following example shows a declaration with an accessor. Two accessors have implicit value parameters called value that accept references to instances or static methods

Public event EventHandler Elapsed

{

Add

{

//... Code executing the + = operator

}

Remove

{

//... Code that executes the-= operator

}

}

When an event accessor is declared, the event does not contain any inline delegate objects. We have to implement our own mechanism for storing and removing events

The event accessor behaves as a void method, i.e. a return statement that returns a value cannot be used

Complete Example:

Declare a delegate

delegate void EventHandler ();

Class MyClass

{

Declare a member variable to hold the event handle (delegate that is invoked when the event is fired)

Private EventHandler M_handler = null;

Firing events

public void Fireaevent ()

{

if (M_handler!= null)

{

M_handler ();

}

}

declaring events

Public event EventHandler Aevent

{

Add accessor

Add

{

Notice that the accessor actually contains an implied parameter named value

The value of this parameter is called by the client program + = Newsletters Hand over delegate

Console.WriteLine ("Aevent Add" is invoked, the value of Hashcode is: "+ value. GetHashCode ());

if (value!= null)

{

Set the M_handler domain to save the new handler

M_handler = value;

}

}

Delete accessor

Remove

{

Console.WriteLine ("Aevent remove is called, Value hashcode is:" + value. GetHashCode ());

if (value = = M_handler)

{

Set M_handler to NULL, the event will no longer be fired

M_handler = null;

}

}

}

}

Class Program

{

static void Main (string[] args)

{

MyClass obj = new MyClass ();

Create a delegate

EventHandler MyHandler = new EventHandler (MyEventHandler);

MyHandler + = MyEventHandle2;

Register a delegate to an event

Obj. Aevent + = MyHandler;

Firing events

Obj. Fireaevent ();

To revoke a delegate from an event

Obj. Aevent-= MyHandler;

Fire events again

Obj. Fireaevent ();

Console.readkey ();

}

Event handlers

static void MyEventHandler ()

{

Console.WriteLine ("This is a event!");

}

Event handlers

static void MyEventHandle2 ()

{

Console.WriteLine ("This is a event2!");

}

}