Learning C#

Multicasting

At times it is desirable to multicast: to call two implementing methods through a single delegate. This becomes particularly important when handling events (discussed later in this chapter).

With multicasting, you create a single delegate that calls multiple encapsulated methods. For example, when a button is pressed, you might want to take more than one action. You could implement this by giving the button a collection of delegates, but it is cleaner and easier to create a single multicast delegate.

Two delegates can be combined with the addition operator (+). The result is a new multicast delegate that invokes both of the original implementing methods. For example, assuming Writer and Logger are delegates, the following line will combine them and produce a new multicast delegate named myMulticastDelegate:

myMulticastDelegate = Writer + Logger;

You can add delegates to a multicast delegate using the plus-equals (+=) operator. This operator adds the delegate on the right side of the operator to the multicast delegate on the left. For example, assuming Transmitter and myMulticastDelegate are delegates, the following line adds Transmitter to myMulticastDelegate:

myMulticastDelegate += Transmitter;

To see how multicast delegates are created and used, let’s walk through a complete example. Example 19-3 is followed by a complete analysis.

Example 19-3. Multicast delegates

using System; namespace DelegatesAndEvents { public class MyClassWithDelegate { // The delegate ...