Flex中对表格中某列的值进行数字格式化保留两位小数

<?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" 
width="100%" height="100%" fontSize="12" 
fontFamily="微软雅黑"> 
<s:layout> 
<s:BasicLayout/> 
</s:layout> 
<fx:Script> 
<![CDATA[ 
import mx.collections.ArrayCollection; 
import mx.events.FlexEvent; 

[Bindable] 
//表格数据绑定 
private var gridArray:ArrayCollection = new ArrayCollection([ 
{week:"星期一",apple:"3676",rate:"0.7868"}, 
{week:"星期二",apple:"4534",rate:"0.65454"}, 
{week:"星期三",apple:"6758",rate:"0.876454"}, 
{week:"星期四",apple:"9808",rate:"0.34224"}, 
{week:"星期五",apple:"6567",rate:"0.9876523"}, 
{week:"星期六",apple:"9000",rate:"0.566777"}, 
{week:"星期日",apple:"4533",rate:"0.988787"} 
]); 

/** 
* 对表格中的比率进行格式化 
*/ 
private function formatDataGrid(item:Object,column:DataGridColumn):String 
{ 
var temp:Number = item.rate; 
var data:String = dataFormatter.format(temp); 
return data; 
} 

]]> 
</fx:Script> 
<fx:Declarations> 
<!--格式化数字--> 
<mx:NumberFormatter id="dataFormatter" precision="2" rounding="up"/> 
</fx:Declarations> 

<mx:VBox width="100%" height="100%" paddingBottom="10" paddingLeft="10" paddingRight="20" 
paddingTop="10" horizontalAlign="center"> 
<mx:DataGrid id="dataGrid" width="100%" height="90%" dataProvider="{gridArray}" textAlign="center"> 
<mx:columns> 
<mx:DataGridColumn headerText="星期" dataField="week"/> 
<mx:DataGridColumn headerText="苹果" dataField="apple"/> 
<mx:DataGridColumn headerText="比率" dataField="rate" labelFunction="formatDataGrid"/> 
</mx:columns> 
</mx:DataGrid> 

</mx:VBox> 
</s:Application>