ActionScript: Correctly casting a bitmap to a class - actionscript

Question

I have tree instance calling an iconFunction "getIconFromItem".
<mx:Tree dataProvider="{collection}" iconFunction="getIconFromItem" />
The getIconFromItem function is returning null even though the bitmap is not null.
public function getIconFromItem(item:Object):Class {
var result:Class = item.icon as Class ;
return result ;
}
Setting a break point on the return result line reveals that item.icon is a bitmap and result is null.
Any ideas or pointers on how to successfully cast a bitmap as class so that the bitmap is returned as an icon?
Cheers
Keith

Answer 1

The problem here is that item.icon is of type Bitmap, which is not extended from the type Class, but from Object. Whenever you cast to a type that is not in the object's type hierarchy, null is returned.
You want to get the class of the icon, which will be instantiated by the tree control, not the icon itself, so you should change your function to
public function getIconFromItem(item:Object):Class {
return item.icon.constructor as Class;
}

Answer 2

The issue was iconFunction expects a class. Each embedded image has a subclass automatically generated by the compiler. Thanks to #weltraumpirat for pointing me in the right direction :-)
The goal was to dynamically display icons in a tree class. It is possible to modify the class created by Ben Stucki (http://blog.benstucki.net/?p=42) to work with the TreeItemRenderer.data object but this failed when I created a custom MXTreeItemRenderer.
Ended up creating a BitmapImage and a custom TreeItemRenderer which used a prefined iconBitmap attribute within a class to dynamically load icons.
package components
{
import flash.display.BitmapData;
import mx.core.mx_internal;
import spark.core.IContentLoader;
import spark.primitives.BitmapImage;
public class RuntimeBitmapImage extends BitmapImage
{
public function RuntimeBitmapImage()
{
super();
}
public function set bitmapData(bitmapData:BitmapData):void
{
super.setBitmapData(bitmapData, false);
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<s:MXTreeItemRenderer xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx" >
<fx:Script>
<![CDATA[
override public function set data(value:Object):void {
super.data = value;
if ( value != null ) {
if ( value.iconBitmap != null ) {
runtimeBitmapImage.bitmapData = value.iconBitmap.bitmapData ;
}
}
}
]]>
</fx:Script>
<s:states>
<s:State name="normal" />
<s:State name="hovered" />
<s:State name="selected" />
</s:states>
<s:HGroup left="0" right="0" top="0" bottom="0" paddingTop="2" verticalAlign="middle">
<s:Rect id="indentationSpacer" width="{treeListData.indent}" percentHeight="100" alpha="0">
<s:fill>
<s:SolidColor color="0xFFFFFF" />
</s:fill>
</s:Rect>
<potentiate:RuntimeBitmapImage id="runtimeBitmapImage" left="2" width="18" />
<s:Label id="labelField" text="{treeListData.label}" paddingTop="2"/>
</s:HGroup>
</s:MXTreeItemRenderer>