AS3 Multiple instance names in one MC - actionscript-3

Question

I apologize for how confusing this question is.
I have a Movie Clip that is a car. In the car movie clip there are four different angles to the car. (e.g. left, right, front back). I dynamically change the body color of the car. In each angle of the car, the body of the car has an instance name "body." I change the color with the code :
var tempcar = "car_mc" + i;
var myNewTransform = new ColorTransform();
myNewTransform.color = 0x000000 //in real life this is a random value
this[tempcar].body.transform.colorTransform = myNewTransform;
Everything works fine, until I tell the car movie clip to gotoAndPlay the frame "front," where we see the front side of the car, and I try and apply the color change again to the body of the front of the car. I get the error :
TypeError: Error #1009: Cannot access a property or method of a null object reference.
Is there a better way to do what I am trying to do?

Answer 1

That's the old ActionScript 2 way of handling things. In ActionScript the container is not always a MovieClip, which would except the hash to access a dynamic field. Also, if you'd added it to the display list via addChild, the result would be different as well, since it is not the case in ActionScript 3, that could address the child automatically.
You should use an Array to store and access dynamically created instances.
// clazz would be the symbol
function createInstance(container:DisplayObjectContainer, clazz:Class, list:Array):Sprite
{
const child:MovieClip = new clazz() as MovieClip;
if (!child) throw new ArgumentError("Wrong type given");
return list[list.length] = container.addChild(child);
}
function getInstanceAt(index:int, list:Array):Sprite
{
return list[index] as Sprite;
}