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>