How can I get the object I am colliding with in Actionscript 3?

Question

Is there a way to know which object an object is colliding with?... I want to create a 'box object' in flash that can identify any other object(Movieclips) that collides with it. For example, if I drop the box on the 'field' (engine or world), and i put anything inside it, I would like the box to tell me what kind of object it is colliding with. I can't use hitTestObject because I don't know which object the box will collide with in advance.

A rough pesudocode to what I want to achieve is as follows:

 if ( Movieclip(parent). UNKNOWN_OBJECT .hitTestObject(this) )
        trace(UNKNOWN_OBJECT.name);

UNKNOWN_OBJECT in the above example doesn't necessarily have the same data type.

Answer 1

You could iterate over all children of the parent at every frame to see if there's any collision occurring. This is a brute-force check though and if you have lots of objects to check collisions against, I suggest you look into Quadtrees or something similar.

Here's an example how your "box object" could check collisions:

// this is your ENTER_FRAME handler
private function handleEnterFrame(evt:Event):void {
    var p:MovieClip = parent as MovieClip;
    if(!p){
        return;
    }
    for(var i:int = 0, len:int = p.numChildren; i < len; i++){
        var child:DisplayObject = p.getChildAt(i);
        if(child != this && this.hitTestObject(child)){
            trace("Collides with: " + getQualifiedClassName(p.getChildAt(i)));
        }
    }
}

All it does is checking collisions with all the child-nodes of the parent (i.e. siblings) every frame. When a collision is detected, it will trace out the class name of the item it collided with. To make this more useful it would be a good idea to dispatch some Event or Signal at the time a collision is detected, so your classes can "listen" for collisions.