21
Events
·Events are specialized delegates that are declared and
invoked by a class that wants to publish notifications.
The event handlers are functions created by an event subscriber and given to the delegate.
The event handlers are functions created by an event subscriber and given to the delegate.
·A C# event uses the specialized delegate event handler
of the form:
public delegate void evDelegate(
object sender, userEventArgs eArgs
);
userEventArgs is a subscriber defined class, derived from System.EventArgs. You usually provide it with a constructor to allow you to specify information for the event to use.
public delegate void evDelegate(
object sender, userEventArgs eArgs
);
userEventArgs is a subscriber defined class, derived from System.EventArgs. You usually provide it with a constructor to allow you to specify information for the event to use.
·The event is then declared by the publisher as:
public event evDelegate evt;
Either publisher or subscriber has to create a delegate object, eveDel, and pass it to the other participant.
public event evDelegate evt;
Either publisher or subscriber has to create a delegate object, eveDel, and pass it to the other participant.
·The event is invoked by the publisher this way:
evDel(
this, new userEventArgs(arg)
);
evDel(
this, new userEventArgs(arg)
);
·The subscriber adds an event handler function,
myOnEvent, to the event delegate this way:
Publisher.evDelegate evDel +=
new Publisher.evDelegate(myOnEvent);
Publisher.evDelegate evDel +=
new Publisher.evDelegate(myOnEvent);