R – In Flex 3 Using a List Component

If it's a dynamic object I believe you can just do something like this:

var obj:Object; // I'm assuming this is your object

for(var id:String in obj) {
  var value:Object = obj[id];

  trace(id + " = " + value);
}

That's how it's done in AS2, and I believe that still works for dynamic objects in AS3. I think the properties that it will show is more limited on non-dynamic objects.

The quickest way is:

<mx:Image id="img" source="{imageTileList.selectedItem.strThumbnail}" />

The data object is for use within an item renderer not outside of it. One data object represents one of the images in your xml that you passed into the renderer.

Be sure to check out the docs for item renderers here.