flex组件使用【PopUpMenuButton】

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
 <mx:XMLList id="xmllist">
  <node label="考试系统"/>
  <node label="培训系统"/>
  <node type="separator"/>
  <node label="关闭系统"/>
 </mx:XMLList>
 <mx:PopUpMenuButton id="popB" itemClick="itemclick(event)" creationComplete="initpop();" labelField="@label" dataProvider="{xmllist}" x="154" y="93" label="PopUpMenuButton"/>
 
 <mx:Script>
  <![CDATA[
   import mx.controls.*;
   import mx.events.*;
   
   private function initpop():void{
    popB.label="--请选择--";
   }
   private function itemclick(event:MenuEvent):void{
    popB.label=event.label;
    Alert.show(event.label+"-"+event.index);
   }
  ]]>
 </mx:Script>
</mx:Application>