Error #2136: The SWF file (swfURL.swf) contains invalid data. at (parent class)

A user submitted question here. He was wondering why he kept getting this error when trying to extend a parent or a super class. I figure I might as well let everyone know the answer. Let me first describe what was going on.

The Situation

I’ll strip out all the non essential code, but he basically had a subclass that was extending the parent class. Nothing too complicated at this point. The problem really arose when he tried to instantiate the subclass in his parent class. Do you see what’s wrong with this picture? Yup, an infinite loop.

When you extend a parent class, you are effectively running it’s constructor function and defining any variables in the parent class. So if you are calling a subclass from the parent class you’re going to end up with an infinite loop and thus the #2136 error.

This boils down to the OOP theories of inheritance and composition. This particular reader was aiming at more of a compositional model rather than inheritance. Google those two OOP terms if you are interested in finding out more about them.

The example code (this is wrong)

//The parent class
package {

	import flash.display.MovieClip;

	public class Parent extends MovieClip {
		public function Parent() {
			var _child:Child = new Child();
		}
	}
}

//Child class
package {

	import flash.display.MovieClip;

	public class Child extends Parent {
		public function Child() {
			trace("Why in the heck doesn't this work?");
		}
	}
}

The above too classes was the gist of what he was doing. You can hopefully see the problem right away. Hopefully this helps someone who gets stuck on this!