EventDispatcher  - AS3

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.

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

function(evt:Event):void

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

Parameters

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

Related API Elements

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

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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

[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.

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.

AIR for TV devices never automatically dispatch this event. You can, however, dispatch it manually.

This event has the following properties:

Related API Elements

[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.

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.

AIR for TV devices never automatically dispatch this event. You can, however, dispatch it manually.

This event has the following properties:

Related API Elements

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));
    }
}