| Language Version: | ActionScript 3.0 |
| Runtime Versions: | AIR 1.0, Flash Player 9, Flash Lite 4 |
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, an event object is dispatched into the event flow from the root of the display list. The event object makes a round-trip journey to the event target, which is conceptually divided into three phases: the capture phase includes the journey from the root to the last node before the event target's node; the target phase includes only the event target node; and the bubbling phase includes 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.
Learn more
| Method | Defined By | ||
|---|---|---|---|
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. | IEventDispatcher | ||
Dispatches an event into the event flow. | IEventDispatcher | ||
Checks whether the EventDispatcher object has any listeners registered for a specific type
of event. | IEventDispatcher | ||
Removes a listener from the EventDispatcher object. | IEventDispatcher | ||
Checks whether an event listener is registered with this EventDispatcher object or any of its ancestors for the specified event type. | IEventDispatcher | ||
addEventListener | () | method |
public function addEventListener(type:String, listener:Function, useCapture:Boolean = false, priority:int = 0, useWeakReference:Boolean = false):void| Language Version: | ActionScript 3.0 |
| Runtime Versions: | AIR 1.0, Flash Player 9, Flash Lite 4 |
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:
| |
useCapture:Boolean (default = false)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) | |
useWeakReference:Boolean (default = false)Class-level member functions are not subject to garbage
collection, so you can set |
dispatchEvent | () | method |
public function dispatchEvent(event:Event):Boolean| Language Version: | ActionScript 3.0 |
| Runtime Versions: | AIR 1.0, Flash Player 9, Flash Lite 4 |
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.
|
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| Language Version: | ActionScript 3.0 |
| Runtime Versions: | AIR 1.0, Flash Player 9, Flash Lite 4 |
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().
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.
|
Boolean — A value of true if a listener of the specified type is registered; false otherwise.
|
Related API Elements
removeEventListener | () | method |
public function removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void| Language Version: | ActionScript 3.0 |
| Runtime Versions: | AIR 1.0, Flash Player 9, Flash Lite 4 |
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)removeEventListener() are required to remove both: one call with useCapture set to true, and another call with useCapture set to false.
|
willTrigger | () | method |
public function willTrigger(type:String):Boolean| Language Version: | ActionScript 3.0 |
| Runtime Versions: | AIR 1.0, Flash Player 9, Flash Lite 4 |
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.
|
Boolean — A value of true if a listener of the specified type will be triggered; false otherwise.
|
decorDispatcher) of the DecoratedDispatcher class is constructed
and the decorDispatcher variable is used to call
addEventListener() with the custom event doSomething, which is
then handled by didSomething(), which prints a line of text using
trace().
package {
import flash.events.Event;
import flash.display.Sprite;
public class IEventDispatcherExample extends Sprite {
public function IEventDispatcherExample() {
var decorDispatcher:DecoratedDispatcher = new DecoratedDispatcher();
decorDispatcher.addEventListener("doSomething", didSomething);
decorDispatcher.dispatchEvent(new Event("doSomething"));
}
public function didSomething(evt:Event):void {
trace(">> didSomething");
}
}
}
import flash.events.IEventDispatcher;
import flash.events.EventDispatcher;
import flash.events.Event;
class DecoratedDispatcher implements IEventDispatcher {
private var dispatcher:EventDispatcher;
public function DecoratedDispatcher() {
dispatcher = new EventDispatcher(this);
}
public function addEventListener(type:String, listener:Function, useCapture:Boolean = false, priority:int = 0, useWeakReference:Boolean = false):void{
dispatcher.addEventListener(type, listener, useCapture, priority);
}
public function dispatchEvent(evt:Event):Boolean{
return dispatcher.dispatchEvent(evt);
}
public function hasEventListener(type:String):Boolean{
return dispatcher.hasEventListener(type);
}
public function removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void{
dispatcher.removeEventListener(type, listener, useCapture);
}
public function willTrigger(type:String):Boolean {
return dispatcher.willTrigger(type);
}
}
Thu Dec 6 2018, 01:12 PM -08:00