How do I modify existing AS3 events so that I can pass data?

Question

So I want a way to set up events so that I can pass data without creating closures \ memory leaks. This is as far as I have got:

package com.events {
    import flash.events.Event;

    public class CustomEvent extends Event {
     public static const REMOVED_FROM_STAGE:String = "removedFromStage";
     public var data:*;

     public function CustomEvent(type:String, customData:*=null, bubbles:Boolean=false, cancelable:Boolean=false) {
      super(type, bubbles, cancelable);
      this.data = customData;
     }

     public override function clone():Event {
      return new CustomEvent(type, data, bubbles, cancelable);
     }

     public override function toString():String {
      return formatToString("CustomEvent", "type", "data", "bubbles", "cancelable", "eventPhase");
     }
    }
}

This gets me the following behavior:

function testme(e:Event) {
    trace(e); 
}

test_mc.addEventListener(CustomEvent.REMOVED_FROM_STAGE, testme);
test_mc.dispatchEvent(new CustomEvent(CustomEvent.REMOVED_FROM_STAGE, 42));
//Traces [CustomEvent type="removedFromStage" data=42 bubbles=false cancelable=false eventPhase=2]
removeChild(test_mc);
//Traces [Event type="removedFromStage" bubbles=false cancelable=false eventPhase=2]

My goal is to get the custom data I want to pass to get passed from the event flash fires, not just the one that I fire. For example, what if I wanted to pass a movieclip along with a loader.COMPLETE event to put the resulting bitmap in?

Answer 1

You extended the Event class for it to dispatch with extra data, now if you want the Loader class to dispatch your custom event type, extend the Loader class to do that (or any other class you want to do this with). In this example I'll override URLLoader with this functionality (because Loader actually dispatches events from it's contentLoaderInfo, which needs two overridden classes, and I just want to keep it simple)

package com.net
{
    import flash.net.URLLoader;
    import flash.events.Event;

    import com.events.CustomEvent;

    public class CustomLoader extends URLLoader
    {
        // URLLoader already has a data property, so I used extraData
        public var extraData:*;

        override public function dispatchEvent(event: Event) : Boolean
        {
            var customEvent: CustomEvent = new CustomEvent(event.type, extraData, event.bubbles, event.cancelable);
            return super.dispatchEvent(customEvent);
        }
    }
}

Now to use this with your CustomEvent class try this code in your .fla

import com.net.CustomLoader;
import com.events.CustomEvent;

var loader: CustomLoader = new CustomLoader();
loader.extraData = "Extra Data";
loader.load(new URLRequest("test.xml"));
loader.addEventListener(Event.COMPLETE, loadComplete);

function loadComplete(event: CustomEvent) : void
{
    trace(event.data); // Extra Data
}

BAM! Custom data on your innately dispatched events!

Answer 2

The following shows the cleanest way to create a custom event. Typically event types have public static references typed in all capitol letters. When an event is dispatched, it passes an Event, or CustomEvent, object to the event handler method. This is where you can retrieve your passed value.

package com.hodgedev.events 
{
    import flash.events.Event;

/**
 * ...
 * @author Brian Hodge([email protected])
 */
    public class CustomEvent extends Event 
    {
        public static const VALUE_CHANGED:String = "VALUE_CHANGED";
        public var value:Number;

        public function CustomEvent(pValue:Number) 
        { 
            super(CustomEvent.VALUE_CHANGED);
            value = pValue;
        } 
        public override function clone():Event 
        { 
            return new CustomEvent(value);
        }
    }
}

When we dispatch events, we create a new instance of the event to be passed as such.

private var _someValue:int = 12;
dispatchEvent(new CustomEvent(_somevalue));

Brian Hodge blog.hodgedev.com