flash builder addChild method error in custom component

I am attempting to make a collapsing list like the ones in google adwords. The compiler is telling me that addChild is not a valid method. Here is my code:

package comps
{
import spark.components.Button;
import spark.components.Group;
import开发者_Go百科 spark.components.TextArea;

public class CollapsibleList extends Group
{

    private var btn : Button = new Button();
    private var list : TextArea = new TextArea();

    public function CollapsibleList()
    {
        super();
        this.btn.width = 100;
        this.btn.height = 20;
        this.btn.label = "My Button";
        this.btn.top = 0;
        this.btn.left = 0;

        this.list.width = 100;
        this.list.height = 200;
        this.list.top = 20;
        this.list.left = 0;

        this.addChild(this.btn);
        this.addChild(this.list);
    }
}
}

I call it simply in main.mxml like so:

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
           xmlns:s="library://ns.adobe.com/flex/spark"
           xmlns:mx="library://ns.adobe.com/flex/mx"
           xmlns:comps="comps.*"
           minWidth="955" minHeight="600">

<comps:CollapsibleList/>

</s:Application>

Im assuimg the compiler isn't lying to me so how do I get those objects (children) to appear?

In Spark, the Flex 4 framework, they've sort of abstracted out the whole "addChild" thing because you're not working with the DisplayList directly. Instead, you have to "addElement()" to a group.

However, addElement requires as a parameter to be an IVisualElement, if I remember correctly. Basically, if you're used to straight old AS3 "addChild()" then you're going to be in for a bit of a learning curve - the payoff is worth it, but it can be difficult.

Here's a blog post that seems to tear into it pretty well, I hope this helps: http://www.billdwhite.com/wordpress/?p=296