flex中popupButton

flex中popupButton.mxml

<?xml version="1.0" encoding="utf-8"?> 
<!--http://www.javaeye.com/topic/210348-->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" creationComplete="initApp()" layout="absolute"> 
    <mx:Style> 
        Application{  
            fontSize:12;  
            backgroundGradientColors: #c0c0c0, #c0c0c0;  
        }  
    </mx:Style> 
    <mx:Script> 
        <![CDATA[ 
            import mx.containers.Panel;      
            import mx.controls.Alert;    
            import mx.events.DropdownEvent; 
 
            private var panel:Panel; 
 
            private function initApp():void { 
                panel = new Panel();  //声明新的Panel 
                panel.title = "panel"; 
                panel.width = 200; 
                panel.height = 200; 
                popBtn.popUp = panel;           //指定popUp目标对象        
                popBtn.addEventListener(DropdownEvent.CLOSE,closeHandler);  //           
                popBtn.open();      //将窗口弹出 
            }            
 
             
            private function closeHandler(evt:DropdownEvent):void{ 
                Alert.show("关闭窗口"); 
            } 
        ]]> 
    </mx:Script> 
    <mx:PopUpButton id="popBtn" label="弹出" width="135"  x="23" y="23"/> 
      
</mx:Application>