AS3 - Event listener that only fires once

问题

I'm looking for a way to add an EventListener which will automatically removes itself after the first time it fires, but I can't figure a way of doing this the way I want to.

I found this function (here) :

public class EventUtil
{
    public static function addOnceEventListener(dispatcher:IEventDispatcher,eventType:String,listener:Function):void
    {
         var f:Function = function(e:Event):void
         {
              dispatcher.removeEventListener(eventType,f);
              listener(e);
          }
          dispatcher.addEventListener(eventType,f);
    }
}

But instead of having to write :

EventUtil.addOnceEventListener( dispatcher, eventType, listener );

I would like to use it the usual way :

dispatcher.addOnceEventListener( eventType, listener );

Has anybody got an idea of how this could be done?
Any help would be greatly apprecitated.

(I know that Robert Penner's Signals can do this, but I can't use them since it would mean a lot of code rewriting that I can't afford for my current project)

回答1:

I find the cleanest way without using statics or messing up your code with noise is to defining a global function (in a file called removeListenerWhenFired.as) like so:

package your.package
{
    import flash.events.Event;
    import flash.events.IEventDispatcher;

    public function removeListenerWhenFired(callback:Function, useCapture:Boolean = false):Function
    {
        return function (event:Event):void
        {
            var eventDispatcher:IEventDispatcher = IEventDispatcher(event.target)
            eventDispatcher.removeEventListener(event.type, arguments.callee, useCapture)
            callback(event)
        }
    }
}

Then you can listen for events like so:

import your.package.removeListenerWhenFired

// ... class definition

    sprite.addEventListener(MouseEvent.CLICKED, 
        removeListenerWhenFired(
            function (event:MouseEvent):void {
                ... do something
            }
        )
    )

回答2:

I've not tried it, but you could just turn the EventUtil static method into a standard method and extend the class in your object.

public class OnceEventDispatcher
{
    public function addOnceEventListener(eventType:String,listener:Function):void
    {
         var f:Function = function(e:Event):void
         {
              this.removeEventListener(eventType,f);
              listener(e);
          }
          this.addEventListener(eventType,f);
    }
}

public class Example extends OnceEventDispatcher
{


}

var ex:Example = new Example();
ex.addOnceEventListener(type, func);

回答3:

functionadd.addEventListener(COMPLETE,functionremove);

functionremove()
{
    runevent();
    functionadd.removeEventListener(COMPLETE,functionremove);
}
function runevent()
{
   trace('Hello');
}

来源：https://stackoverflow.com/questions/2476386/as3-event-listener-that-only-fires-once

标签

actionscript-3

events

addeventlistener

dispatch