package;
import flash.events.Event;
import flash.events.EventDispatcher;
import flash.events.IEventDispatcher;

class EventDispatcherTools 
{
    public static function addOnceListener (dispatcher:IEventDispatcher, type : String, listener : Event->Void) 
    {
        var f:Event->Void = null;
        f = function (e:Event) {
            cast (e.target, IEventDispatcher).removeEventListener(e.type, f);
            listener(e);
        }
        dispatcher.addEventListener(type, f);
    }
}

// usage
using Main.EventDispatcherTools;

class Main 
{
    public static function main ():Void 
    {
        var e : EventDispatcher = new EventDispatcher();
        // add a listener which is called only once
        e.addOnceListener(Event.COMPLETE, function (_) trace("complete, listener will be removed after first call."));
        
        trace(e.hasEventListener(Event.COMPLETE)); // yes there is a listener
        
        e.dispatchEvent(new Event(Event.COMPLETE)); // first dispatch
        
        trace(e.hasEventListener(Event.COMPLETE)); // no listener, it's automatically removed
    }
}