How to detect value change of item?

Question

Hi all,
We want to list all goods that customer chooses, so TileList is used to display all goods information and a custom component MyItem is used as ItemRenderer. Meanwhile a Label is used to display the sum of all the goods. The hierarchy is simply like this:
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"  layout="absolute" >
<mx:TileList id="tl" dataProvider="{acGoods}" ItemRenderer="MyItem"/>
<mx:Label id="labelSum"/>
</mx:Application>
Here, acGoods is an ArrayCollection which I believe is bindable.
User may change price inside MyItem directly, so the text of the Label need to update as well. I find that acGoods contains latest price. Now the problem is Label text stays the same. I have tried to call calculating function in set acGoods() but it doesn't work.
Please don't sugguest dispatch event because this is only a simplified scenario. If anybody tell me how to implement this by binding mechaism, that'll be very helpful.
Best wishes,

Answer 1

protected function get totalLabelText():string {
    // for each var i:* in acGoods and so on
    return 'Calculated label here';
<mx:Label id="labelSum" text="{totalLabelText}"/>
Inside MyItem:
once you changed something invoke:
Application.application.executeBindings(true);
Hope this will work for you