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Class EventDispatcher

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.

:event

activate [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.

:event

deactivate [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.

Hierarchy

Implements

Index

Constructors

constructor

  • 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

    • Optional target: IEventDispatcher

      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.

    Returns EventDispatcher

Methods

addEventListener

  • addEventListener(type: string, listener: function, useCapture?: boolean, priority?: number, useWeakReference?: boolean): 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 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).

    throws

    ArgumentError The listener specified is not a function.

    Parameters

    • type: string

      The type of event.

    • listener: function
        • (event: object): void
        • Parameters

          • event: object

          Returns void

    • Optional useCapture: boolean

      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.

    • Optional priority: number

      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.

    • Optional useWeakReference: boolean

      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 garbage-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.
      

    Returns void

dispatchEvent

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

    throws

    Error The event dispatch recursion limit has been reached.

    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.

    Returns 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.

hasEventListener

  • 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 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.

    Returns boolean

    A value of true if a listener of the specified type is registered; false otherwise.

removeEventListener

  • removeEventListener(type: string, listener: function, useCapture?: boolean): 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
        • (event: object): void
        • Parameters

          • event: object

          Returns void

    • Optional useCapture: boolean

      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.

    Returns void

toString

  • toString(): string

willTrigger

  • 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 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.

    Returns boolean

    A value of true if a listener of the specified type will be triggered; false otherwise.

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