Flex4 DataGrid添加CheckBox及动态添加数据

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955" minHeight="600">
<s:layout>
<s:VerticalLayout/>
</s:layout>

<fx:Script>
<![CDATA[
import mx.collections.ArrayCollection;
import mx.events.FlexEvent;
[Bindable]
public var arr:ArrayCollection = new ArrayCollection([{id:1,name:"芒果",count:1000, selected:"true"},
{id:2,name:"香蕉",count:2120, selected:"false"}, {id:3,name:"苹果",count:3000, selected:"true"},
{id:3,name:"桔子",count:3000, selected:"false"}]);

protected function button1_clickHandler(event:MouseEvent):void
{
var o:Object = new Object();
o.name = "aaa";
o.count = 1122;
o.selected = "true";
arr.addItem(o);
}
]]>
</fx:Script>
<fx:Declarations>
<!-- 将非可视元素（例如服务、值对象）放在此处 -->
</fx:Declarations>
<s:Button label="添加数据" click="button1_clickHandler(event)"/>
<s:DataGrid dataProvider="{arr}" width="400" height="300">
<s:columns>
<s:ArrayList>
<s:GridColumn headerText="序号" dataField="id" editable="false" />
<s:GridColumn headerText="名称" dataField="name" editable="false"/>
<s:GridColumn headerText="数量" dataField="count" editable="false"/>
<s:GridColumn>
<s:itemRenderer>
<fx:Component>
<s:GridItemRenderer>

<fx:Script>
<![CDATA[
protected function getSelected(s:String):Boolean//防止有滚动条时显示异常
{
if(s == "true")
{
return true;
}
return false;
}
]]>
</fx:Script>

<s:CheckBox selected="{getSelected(data.selected)}"/>
</s:GridItemRenderer>
</fx:Component>
</s:itemRenderer>
</s:GridColumn>
</s:ArrayList>
</s:columns>
</s:DataGrid>
</s:Application>