flex advancedDatagrid 自动生成序号

<mx:HBox xmlns:mx="http://www.adobe.com/2006/mxml"  horizontalAlign="center">
	<mx:Script>
		<![CDATA[
			import mx.controls.AdvancedDataGrid;
			import mx.controls.Alert;
			import mx.events.FlexEvent;
			
			override public function set data(value:Object):void
			{      
				if(value != null)
				{
					super.data = value;
					LbSequence.text=((this.owner as AdvancedDataGrid).dataProvider.getItemIndex(value)+1).toString();
					
				}
			}    
		]]>
	</mx:Script>
	
	<mx:Label  id="LbSequence" />
</mx:HBox> 

<mx:AdvancedDataGridColumn headerText="序号"  itemRenderer=" cn.edu.whu.liesmars.renderer.SequenceItemRenderer"/>