Ans:

The ListData class defines the data type of the listData property implemented by drop-in item renderers or drop-in item editors for the List control. All drop-in item renderers and drop-in item editors must implement the IDropInListItemRenderer interface, which defines the listData property.

While the properties of this class are writable, you should consider them to be read only. They are initialized by the List class, and read by an item renderer or item editor. Changing these values can lead to unexpected results.

for example:

<?xml version="1.0" encoding="utf-8"?> 
<mx:HBox xmlns:mx="http://www.adobe.com/2006/mxml" 
verticalAlign="middle" paddingRight="4" paddingLeft="4" >  
<mx:Script>  
<![CDATA[ 
public function get quantity() : Number 
{
return itemQuantity.value;
} 
]]>  
</mx:Script>  
<mx:CurrencyFormatter id="cfmt" precision="2" />  
<mx:Label text="{data.name}" fontWeight="bold" 
fontSize="12"/> 
<mx:Spacer width="100%"/>  
<mx:NumericStepper id="itemQuantity" 
value="{data.quantity}" minimum="0" maximum="100"/> 
<mx:Label text="{cfmt.format(data.price*itemQuantity.value)}"
 width="66"/>
</mx:HBox>