Air Mobile List Custom Layout

Question

Hello Everyone,
  I am working with Adobe Air and I am making a mobile app.  I want a custom list layout so I thought I would try some examples I found on the web.  Unfortunately, most of these examples choke.  They generally have code in the updateDisplayList call that resembles this.
override public function updateDisplayList( width:Number, height:Number ):void
     super.updateDisplayList( width, height );
     var layoutTarget:GroupBase = target;
     for( var i:int =  0 ; i < layoutTarget.numElements; i++ )
          element = layoutTarget.getElementAt( i ) as IVisualElement;
          CRASHES HERE --> element.setLayoutBoundsSize( NaN , NaN );
          element.setLayoutBoundsPosition( xpos , ypos );
The issue I have found is that even though "layoutTarget.numElements" = 1, layoutTarget.getElementAt( i ) returns null, even when I don't cast it to anything. 
I've investigated looking at the TileLayout and VerticalLayout code, but I'm not quite sure I can even devise what is going on in there; they don't appear to be doing the stuff I am accustomed to seeing in the updateDIsplayList call.
Any help is greatly appreciated.

Answer 1

Yes, at first I thought it was a failed casting operation.  But upon further examination that wasn't the case.  For instance, the "thing" object in the following code is null, even though the layoutTarget.numElements = 1.
for( var i:int = 0; i < layoutTarget.numElements; i++ )
    var thing:Object = layoutTarget.getElementAt(i);
    //the "thing" is null
For background information, I am using the layout code from the Flex 4 Cookbook by O'Reilly found on page 96.
Any help is greatly appreciated.