Language Version: | ActionScript 3.0 |
Runtime Versions: | Flash Player 9, AIR 1.0 |
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.
Method | Defined By | ||
---|---|---|---|
EventDispatcher(target:IEventDispatcher = null)
Aggregates an instance of the EventDispatcher class. | EventDispatcher | ||
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 | ||
Indicates whether an object has a specified property defined. | Object | ||
Indicates whether an instance of the Object class is in the prototype chain of the object specified
as the parameter. | Object | ||
Indicates whether the specified property exists and is enumerable. | Object | ||
Removes a listener from the EventDispatcher object. | EventDispatcher | ||
Sets the availability of a dynamic property for loop operations. | Object | ||
Returns the string representation of this object, formatted according to locale-specific conventions. | Object | ||
Returns the string representation of the specified object. | Object | ||
Returns the primitive value of the specified object. | Object | ||
Checks whether an event listener is registered with this EventDispatcher object or any of
its ancestors for the specified event type. | EventDispatcher |
Event | Summary | Defined By | ||
---|---|---|---|---|
[broadcast event] Dispatched when the Flash Player or AIR application gains operating system focus and becomes active. | EventDispatcher | |||
[broadcast event] Dispatched when the Flash Player or AIR application operating loses system focus and is becoming inactive. | EventDispatcher |
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.
Parameterstarget: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.
|
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: | Flash Player 9, AIR 1.0 |
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 removeListener()
. Then you can register the
listener again with the new priority level.
Keep in mind that after the listener is registered, subsequent calls to
addEventListener()
with a different type
or
useCapture
value 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.
If you no longer need an event listener, remove it by calling
removeEventListener()
, or memory problems could result. Event listeners are not automatically
removed from memory because the garbage
collector does not remove the listener as long as the dispatching object exists (unless the useWeakReference
parameter is set to true
).
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 being processed on this node, the event listener is not triggered during the current phase but can 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 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 The function can have any name. | |
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. The priority is designated by
a signed 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 |
Throws
ArgumentError — The listener specified is not a function.
|
dispatchEvent | () | method |
public function dispatchEvent(event:Event):Boolean
Language Version: | ActionScript 3.0 |
Runtime Versions: | Flash Player 9, AIR 1.0 |
Dispatches an event into the event flow. The event target is the EventDispatcher
object upon which the dispatchEvent()
method is called.
Parameters
event:Event — The Event object that is dispatched into the event flow.
If the event is being redispatched, a clone of the event is created automatically.
After an event is dispatched, its target property cannot be changed, so you
must create a new copy of the event for redispatching to work.
|
Boolean — A value of true if the event was successfully dispatched. A value of false indicates failure or that preventDefault() was called
on the event.
|
Throws
Error — The event dispatch recursion limit has been reached.
|
hasEventListener | () | method |
public function hasEventListener(type:String):Boolean
Language Version: | ActionScript 3.0 |
Runtime Versions: | Flash Player 9, AIR 1.0 |
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 actually triggers an event listener, use 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.
When hasEventListener()
is called from a LoaderInfo object, only the
listeners that the caller can access are considered.
Parameters
type:String — The type of event.
|
Boolean — A value of true if a listener of the specified type is registered;
false otherwise.
|
See also
removeEventListener | () | method |
public function removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void
Language Version: | ActionScript 3.0 |
Runtime Versions: | Flash Player 9, AIR 1.0 |
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 .
|
willTrigger | () | method |
public function willTrigger(type:String):Boolean
Language Version: | ActionScript 3.0 |
Runtime Versions: | Flash Player 9, AIR 1.0 |
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 the hasEventListener()
and the willTrigger()
methods is that hasEventListener()
examines only the object to which it belongs,
whereas the willTrigger()
method examines the entire event flow for the event specified by the
type
parameter.
When willTrigger()
is called from a LoaderInfo object, only the
listeners that the caller can access are considered.
Parameters
type:String — The type of event.
|
Boolean — A value of true if a listener of the specified type will be triggered; false otherwise.
|
activate | Event |
flash.events.Event
property Event.type =
flash.events.Event.ACTIVATE
Language Version: | ActionScript 3.0 |
Runtime Versions: | Flash Player 9, AIR 1.0 |
[broadcast event] Dispatched when the Flash Player or AIR application gains operating system focus and becomes active. This event is a broadcast event, which means that it is dispatched by all EventDispatcher objects with a listener registered for this event. For more information about broadcast events, see the DisplayObject class.
TheACTIVATE
constant defines the value of the type
property of an activate
event object.
Note: This event has neither a "capture phase" nor a "bubble phase", which means that event listeners must be added directly to any potential targets, whether the target is on the display list or not.
This event has the following properties:
Property | Value |
---|---|
bubbles | false |
cancelable | false ; there is no default behavior to cancel. |
currentTarget | The object that is actively processing the Event object with an event listener. |
target | Any DisplayObject instance with a listener registered for the activate event. |
See also
deactivate | Event |
flash.events.Event
property Event.type =
flash.events.Event.DEACTIVATE
Language Version: | ActionScript 3.0 |
Runtime Versions: | Flash Player 9, AIR 1.0 |
[broadcast event] Dispatched when the Flash Player or AIR application operating loses system focus and is becoming inactive. This event is a broadcast event, which means that it is dispatched by all EventDispatcher objects with a listener registered for this event. For more information about broadcast events, see the DisplayObject class.
TheEvent.DEACTIVATE
constant defines the value of the type
property of a deactivate
event object.
Note: This event has neither a "capture phase" nor a "bubble phase", which means that event listeners must be added directly to any potential targets, whether the target is on the display list or not.
This event has the following properties:
Property | Value |
---|---|
bubbles | false |
cancelable | false ; there is no default behavior to cancel. |
currentTarget | The object that is actively processing the Event object with an event listener. |
target | Any DisplayObject instance with a listener registered for the deactivate event. |
See also
EventDispatcherExample
and
CustomDispatcher
, a subclass of EventDispatcher
, to show how a
custom event is created and dispatched. The example carries out the following tasks:
- The constructor of
EventDispatcherExample
creates a local variabledispatcher
and assigns it to a new CustomDispatcher instance. - Inside
CustomDispatcher
, a string is set so that the event has the nameaction
, and thedoAction()
method is declared. When called, this method creates theaction
event and dispatches it usingEventDispatcher.dispatchEvent()
. - The
dispatcher
property is then used to add theaction
event listener and associated subscriber methodactionHandler()
, which simply prints information about the event when it is dispatched. - The
doAction()
method is invoked, dispatching theaction
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)); } }
Fri Mar 19 2010, 02:45 AM -07:00