Packageflash.events
Classpublic class EventDispatcher
InheritanceEventDispatcher Inheritance Object
Implements IEventDispatcher
Subclasses Timer

Language Version : ActionScript 3.0
Runtime Versions : Flash Player 9, AIR 1.0

The EventDispatcher class is the base class for all classes that dispatch events. The EventDispatcher class implements the IEventDispatcher interface and is the base class for the DisplayObject class. The EventDispatcher class allows any object on the display list to be an event target and as such, to use the methods of the IEventDispatcher interface.

Event targets are an important part of the Flash® Player and Adobe® AIR® event model. The event target serves as the focal point for how events flow through the display list hierarchy. When an event such as a mouse click or a keypress occurs, Flash Player or the AIR application dispatches an event object into the event flow from the root of the display list. The event object then makes its way through the display list until it reaches the event target, at which point it begins its return trip through the display list. This round-trip journey to the event target is conceptually divided into three phases: the capture phase comprises the journey from the root to the last node before the event target's node, the target phase comprises only the event target node, and the bubbling phase comprises any subsequent nodes encountered on the return trip to the root of the display list.

In general, the easiest way for a user-defined class to gain event dispatching capabilities is to extend EventDispatcher. If this is impossible (that is, if the class is already extending another class), you can instead implement the IEventDispatcher interface, create an EventDispatcher member, and write simple hooks to route calls into the aggregated EventDispatcher.

View the examples

See also

Manually dispatching events
Using event subclasses
About the EventDispatcher class
Event propagation
Event priorities
About keyboard events
Handling events for display objects


Public Properties
 PropertyDefined By
  _listeners : Array
EventDispatcher
  _listenersCalls : Array
EventDispatcher
  _listenersNames : Array
EventDispatcher
  _objectlist : Array
[static]
EventDispatcher
  _objectmap : Array
[static]
EventDispatcher
Public Methods
 MethodDefined By
  
Aggregates an instance of the EventDispatcher class.
EventDispatcher
 Inherited
_init():*
[static]
_init
  
addEventListener(type:String, listener:Function, useCapture:Boolean = false, priority:int = 0, useWeakReference:Boolean = false):void
Registers an event listener object with an EventDispatcher object so that the listener receives notification of an event.
EventDispatcher
  
Dispatches an event into the event flow.
EventDispatcher
  
Checks whether the EventDispatcher object has any listeners registered for a specific type of event.
EventDispatcher
 Inherited
AS3
 Inherited
init():*
[static]
init
 Inherited
AS3
 Inherited
AS3
  
removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void
Removes a listener from the EventDispatcher object.
EventDispatcher
  
EventDispatcher
  
Checks whether an event listener is registered with this EventDispatcher object or any of its ancestors for the specified event type.
EventDispatcher
Protected Methods
 MethodDefined By
 Inherited
[static]
protected
 Inherited
_setPropertyIsEnumerable(o:*, V:String, enumerable:Boolean):void
[static]
protected
Public Constants
 ConstantDefined By
 Inheritedlength : int = 1
[static]
length
Property Detail
_listenersproperty
public var _listeners:Array

_listenersCallsproperty 
public var _listenersCalls:Array

_listenersNamesproperty 
public var _listenersNames:Array

_objectlistproperty 
public static var _objectlist:Array

_objectmapproperty 
public static var _objectmap:Array

Constructor Detail
EventDispatcher()Constructor
public function EventDispatcher(target:IEventDispatcher = null)

Language Version : ActionScript 3.0
Runtime Versions : Flash Player 9, AIR 1.0

Aggregates an instance of the EventDispatcher class.

The EventDispatcher class is generally used as a base class, which means that most developers do not need to use this constructor function. However, advanced developers who are implementing the IEventDispatcher interface need to use this constructor. If you are unable to extend the EventDispatcher class and must instead implement the IEventDispatcher interface, use this constructor to aggregate an instance of the EventDispatcher class.

Parameters
target:IEventDispatcher (default = null) — The target object for events dispatched to the EventDispatcher object. This parameter is used when the EventDispatcher instance is aggregated by a class that implements IEventDispatcher; it is necessary so that the containing object can be the target for events. Do not use this parameter in simple cases in which a class extends EventDispatcher.
Method Detail
addEventListener()method
public function addEventListener(type:String, listener:Function, useCapture:Boolean = false, priority:int = 0, useWeakReference:Boolean = false):void

Registers an event listener object with an EventDispatcher object so that the listener receives notification of an event. You can register event listeners on all nodes in the display list for a specific type of event, phase, and priority.

After you successfully register an event listener, you cannot change its priority through additional calls to addEventListener(). To change a listener's priority, you must first call removeEventListener(). Then you can register the listener again with the new priority level.

After the listener is registered, subsequent calls to addEventListener() with a different value for either type or useCapture result in the creation of a separate listener registration. For example, if you first register a listener with useCapture set to true, it listens only during the capture phase. If you call addEventListener() again using the same listener object, but with useCapture set to false, you have two separate listeners: one that listens during the capture phase, and another that listens during the target and bubbling phases.

You cannot register an event listener for only the target phase or the bubbling phase. Those phases are coupled during registration because bubbling applies only to the ancestors of the target node.

When you no longer need an event listener, remove it by calling EventDispatcher.removeEventListener(); otherwise, memory problems might result. Objects with registered event listeners are not automatically removed from memory because the garbage collector does not remove objects that still have references.

Copying an EventDispatcher instance does not copy the event listeners attached to it. (If your newly created node needs an event listener, you must attach the listener after creating the node.) However, if you move an EventDispatcher instance, the event listeners attached to it move along with it.

If the event listener is being registered on a node while an event is also being processed on this node, the event listener is not triggered during the current phase but may be triggered during a later phase in the event flow, such as the bubbling phase.

If an event listener is removed from a node while an event is being processed on the node, it is still triggered by the current actions. After it is removed, the event listener is never invoked again (unless it is registered again for future processing).

Parameters

type:String — The type of event.
 
listener:Function — The listener function that processes the event. This function must accept an event object as its only parameter and must return nothing, as this example shows:
		 function(evt:Event):void
		 
 
useCapture:Boolean (default = false) — Determines whether the listener works in the capture phase or the target and bubbling phases. If useCapture is set to true, the listener processes the event only during the capture phase and not in the target or bubbling phase. If useCapture is false, the listener processes the event only during the target or bubbling phase. To listen for the event in all three phases, call addEventListener() twice, once with useCapture set to true, then again with useCapture set to false.
 
priority:int (default = 0) — The priority level of the event listener. Priorities are designated by a 32-bit integer. The higher the number, the higher the priority. All listeners with priority n are processed before listeners of priority n-1. If two or more listeners share the same priority, they are processed in the order in which they were added. The default priority is 0.
 
useWeakReference:Boolean (default = false) — Determines whether the reference to the listener is strong or weak. A strong reference (the default) prevents your listener from being garbage-collected. A weak reference does not. Class-level member functions are not subject to garbage collection, so you can set useWeakReference to true for class-level member functions without subjecting them to garbage collection. If you set useWeakReference to true for a listener that is a nested inner function, the function will be garbge-collected and no longer persistent. If you create references to the inner function (save it in another variable) then it is not garbage-collected and stays persistent.

dispatchEvent()method 
public function dispatchEvent(event:Event):Boolean

Dispatches an event into the event flow. The event target is the EventDispatcher object upon which dispatchEvent() is called.

Parameters

event:Event — The event object dispatched into the event flow.

Returns
Boolean — A value of true unless preventDefault() is called on the event, in which case it returns false.
hasEventListener()method 
public function hasEventListener(type:String):Boolean

Checks whether the EventDispatcher object has any listeners registered for a specific type of event. This allows you to determine where an EventDispatcher object has altered handling of an event type in the event flow hierarchy. To determine whether a specific event type will actually trigger an event listener, use IEventDispatcher.willTrigger().

Parameters

type:String — The type of event.

Returns
Boolean — A value of true if a listener of the specified type is registered; false otherwise.
removeEventListener()method 
public function removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void

Removes a listener from the EventDispatcher object. If there is no matching listener registered with the EventDispatcher object, a call to this method has no effect.

Parameters

type:String — The type of event.
 
listener:Function — The listener object to remove.
 
useCapture:Boolean (default = false) — Specifies whether the listener was registered for the capture phase or the target and bubbling phases. If the listener was registered for both the capture phase and the target and bubbling phases, two calls to removeEventListener() are required to remove both: one call with useCapture set to true, and another call with useCapture set to false.

toString()method 
public function toString():String

Returns
String
willTrigger()method 
public function willTrigger(type:String):Boolean

Checks whether an event listener is registered with this EventDispatcher object or any of its ancestors for the specified event type. This method returns true if an event listener is triggered during any phase of the event flow when an event of the specified type is dispatched to this EventDispatcher object or any of its descendants.

The difference between hasEventListener() and willTrigger() is that hasEventListener() examines only the object to which it belongs, whereas willTrigger() examines the entire event flow for the event specified by the type parameter.

Parameters

type:String — The type of event.

Returns
Boolean — A value of true if a listener of the specified type will be triggered; false otherwise.
Examples
The following example uses the classes EventDispatcherExample and CustomDispatcher, a subclass of EventDispatcher, to show how a custom event is created and dispatched. The example carries out the following tasks:
  1. The constructor of EventDispatcherExample creates a local variable dispatcher and assigns it to a new CustomDispatcher instance.
  2. Inside CustomDispatcher, a string is set so that the event has the name action, and the doAction() method is declared. When called, this method creates the action event and dispatches it using EventDispatcher.dispatchEvent().
  3. The dispatcher property is then used to add the action event listener and associated subscriber method actionHandler(), which simply prints information about the event when it is dispatched.
  4. The doAction() method is invoked, dispatching the action event.
     package
     {
             import flash.display.Sprite;
             import flash.events.Event;
     
             public class EventDispatcherExample extends Sprite
             {
                 public function EventDispatcherExample()
                 {
                     var dispatcher:CustomDispatcher = new CustomDispatcher();
                     dispatcher.addEventListener( CustomDispatcher.ACTION, actionHandler );
                     dispatcher.doAction();
                 }
     
                 private function actionHandler( event:Event ):void
                 {
                     trace( "actionHandler: " + event );
                 }
             }
     }
                  import flash.events.EventDispatcher;
             import flash.events.Event;
     
             class CustomDispatcher extends EventDispatcher
             {
                 public static var ACTION:String = "action";
     
                 public function doAction():void
                 {
                     dispatchEvent( new Event( CustomDispatcher.ACTION ) );
                 }
             }