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>