ActionScript 3 subclass' method inheritance issue

Question

I have a class Goo like this:

public class Goo extends Node
{
    public function Update(dt:Number):void
    {
        // function to be overriden
        trace("updating Goo");
    }
}

and a subclass of Goo called GooX:

public class GooX extends Goo
{
    override public function Update(dt:Number):void
    {
        trace("updating GooX");
    }
}

and another called GooY:

public class GooY extends Goo
{
    override public function Update(dt:Number):void
    {
        trace("updating GooY");
    }
}

and then a Manager which creates Goo objects and updates them like this:

public class Manager
{
    private var gooArray:Vector.<Goo> = new Vector.<Goo>();

    public function Manager():void
    {
        var aGoo:Goo;
        if (Math.random() >= 0.5)
        {
            aGoo = new GooX();
        }
        else
        {
            aGoo = new GooY();
        }
        gooArray.push(aGoo);
    }

    public function Update(dt:Number):void
    {
        for (var i:int = 0; i < gooArray.length; i++)
        {
            gooArray[i].Update(dt);
        }
    }
}

this code always shows "updating Goo" in the trace log. I tried also detecting which type is it by doing a gooArray[i] is GooX or gooArray[i] is GooY but it's always false for both. Even if I force a cast with gooArray[i] as GooX it will always say that the object is null.

Does anybody knows a way to do what I'm trying to do (let the Update of the child class being called instead of the one of the parent class)? Thanks.

I just put in the code you posted here almost verbatim and I don't get the same results as you. The overridden method gets called for me, so I think you have something else going on. — J. Holmes
– J. Holmes, Commented Jan 20, 2012 at 21:24
Classes work just fine for me. Flash Player 11.0.1.152 compiled in FlashBuilder with Flex 4.1 SDK. Output I get is "updating GooX". If I plug it into an ENTER_FRAME loop, I get a fairly even dispersal between GooX and GooY. — meddlingwithfire
– meddlingwithfire, Commented Jan 20, 2012 at 21:24
That's weird, I'm running it using Flash Builder 4.6 with Flex SDK 4.1 and Flash Player 11. It doesn't work. — jglievano
– jglievano, Commented Jan 20, 2012 at 21:39

Jonathan Dunlap · Accepted Answer · 2012-01-20 22:12:33Z

2

You're example is logically correct to Actionscript3, but your confusion might be caused on the manager's constructor since it makes a random object of either type. To better test the problem, replace the manager's constructor with:

public function Manager():void
{
    gooArray.push(new GooY());
    gooArray.push(new GooX());
}

This problem might be an odd bug in the compiler that you are using. Try upgrading to the latest SDK, do a clean project, and see if you still get the same issue.

Lastly, what is this "Node" object? Perhaps, as a highly improbable idea, that Node is some kind of Object Proxy that is hijacking method calls. However, I doubt this applies to your project.

answered Jan 20, 2012 at 22:12

Jonathan Dunlap

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1 Comment

jglievano Over a year ago

Thanks, you are right, the example is logically correct and is working right on its own. I think I might have found the problem. Of course the example code belongs to a wider project and I was abstracting the relevant part in case I was missing something (I'm not expert in AS3). The problem was that someone was cloning the subclassed Goo object and making it a Goo object again. Maybe a reason why abstract classes are so important?

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