Progress bar Fl cs3 as3.0

below is my very simple code to load images from a instance of button component into an instance of UIloader component.

there are multiple buttons like this one

i can’t get it… the way to get progress bar to listen and respond to the loading of the image

img_02_btn.addEventListener(MouseEvent.CLICK, onClick2);
function onClick2(event:MouseEvent):void
{
trace(“typeMe”);
loaderOne.source = “assets/b300.png”;
loaderOne.load();

}