flex dataGrid 中的checkBox 问题 （急，急，急）

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
<mx:Script>
<![CDATA[
import mx.events.FlexEvent;
import mx.collections.ArrayCollection;
[Bindable]
private var dataSource:ArrayCollection = new ArrayCollection([ 
{id:'一班'},
  {id:1,name:"test1",age:12,select:''}, 
  {id:2,name:"test2",age:40,select:''}, 
  {id:3,name:"test3",age:20,select:''}, 
  {id:'二班'},
  {id:4,name:"test4",age:18,select:''}, 
  {id:5,name:"test5",age:60,select:''}, 
  ]); 
 



]]>
</mx:Script>
<mx:DataGrid id="adGrid" width="300" height="253" fontSize="14" dataProvider="{dataSource}" x="262.5" y="203"> 
<mx:columns> 
<mx:DataGridColumn headerText="序号" dataField="id"/> 
<mx:DataGridColumn headerText="名称" dataField="name" /> 
 
<mx:DataGridColumn headerText="是否选择" dataField="age" textAlign="center" >
<mx:itemRenderer>