Every object in the display list can trace its class inheritance back to the DisplayObject class. The DisplayObject class, in turn, inherits from the EventDispatcher class. The EventDispatcher class is a base class that provides important event model functionality for every object on the display list. Because the DisplayObject class inherits from the EventDispatcher class, any object on the display list has access to the methods of the EventDispatcher class.

This is significant because every item on the display list can participate fully in the event model. Every object on the display list can use its addEventListener() method--inherited from the EventDispatcher class--to listen for a particular event, but only if the listening object is part of the event flow for that event.

Although the name EventDispatcher seems to imply that this class's main purpose is to send (or dispatch) Event objects, the methods of this class are used much more frequently to register event listeners, check for event listeners, and remove event listeners.

The EventDispatcher class implements the IEventDispatcher interface. This allows developers who create custom classes that cannot inherit from EventDispatcher or one of its subclasses to implement the IEventDispatcher interface to gain access to its methods.

The addEventListener() method is the most commonly used method of this class. You use it to register your event listeners. For information on using the addEventListener() method, see Using the addEventListener() method.

Advanced programmers use the dispatchEvent() method to manually dispatch an event or to send a custom Event object into the event flow. For more information, see Manually dispatching events.

Several other methods of the EventDispatcher class provide useful information about the existence of event listeners. The hasEventListener() method returns true if an event listener is found for that specific event type on a particular display list object. The willTrigger() method checks for event listeners on a particular display list object, but it also checks for listeners on all of that display list object's ancestors for all phases of the event flow. The method returns true if it finds one.