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

update functions. The subscribe and unsubscribe functions are the same as previous
Observer designs in this chapter. Save the classes in Example 8-15 and Example 8-16
by their caption names.
Example 8-15. Subject.as
package
{
//Subject Interface
public interface Subject
{
function subscribeObserver(o:Observer):void;
function unsubscribeObserver(o:Observer):void;
function notifyObserver(score:Number,damage:String):void;
}
}
Example 8-16. Observer.as
package
{
//Observer Interface
public interface Observer
{
function update(score:Number,damage:String):void;
}
}
Giving More Work to the Concrete Classes
The two classes representing concrete subjects and observers are changed little from
previous examples. The ConcreteSubject class still keeps track of who has subscribed
and unsubscribed, and sends out notifications of state changes.
The ConcreteObserver class, though, has taken on another responsibility. When a
new ConcreteObserver is created, it makes sense to automatically subscribe her to the
notification process. So instead of making it a two-step process, one to instantiate
and another to subscribe, the ConcreteObserver now automatically subscribes new
instances. To do this, only a single line had to be added to the constructor function:
concreteObserver.subscribeObserver(this);
The parameter references the instance being instantiated. At any time, the instance
can unsubscribe or resubscribe by calling the unsubscribe or subscribe functions.
Example 8-17 and Example 8-18 should be saved using the caption names.
Dynamically Changing States | 303