ActionScript 3.0 Design Patterns.pdf - VideoTutorials-bg.com

this all work right is the use of an array to hold the subscribing observers, and a distribution
method for broadcasting the current state.
Subject Interface
All we need for the Subject interface are three methods to take care of the subscription
and notification work. Because all of the functions in an interface construct are
abstract, we don’t have a lot of detail to address. However, we’ve got to be careful to
be sure that all the necessary parts are in place. Example 8-5 shows the script to be
saved as Subject.as:
Example 8-5. Subject.as
package
{
//Subject Interface
public interface Subject
{
function subscribeObserver(o:Observer):void;
function unsubscribeObserver(o:Observer):void;
function notifyObserver( ):void;
}
}
In the first two functions, you’ll see evidence of composition. The “o” parameter is an
Observer datatype, which is a reference to another interface that’ll be built as part of
the Observer design pattern. If you look at the diagram in Figure 8-2, you’ll see an
arrow from the abstract Subject to the abstract Observer. That reference to the
Observer datatype is part of the process that uses composition rather than
inheritance.
Observer Interface
The Observer interface is deceptively simple. The single update( ) function is actually
part of the composition between the Observer and Subject structures. However, we
see the composition only when we look at the connection between the concrete
observer and subject through the update( ) supertype in the Observer interface. Save
the code in Example 8-6 as Observer.as:
Example 8-6. Observer.as
package
{
//Observer Interface
public interface Observer
{
function update(light:String):void;
}
}
290 | Chapter 8: Observer Pattern