Alert 加监听事件

import mx.events.CloseEvent; 
   private var alert:Alert;
   public function buttonClick():void{
    if( EditAdd1.text=="" ){
     Alert.buttonWidth = 100;
     Alert.yesLabel = "确定";
     Alert.buttonHeight = 30;
     alert=Alert.show("请输入被加数","提示",1,this);
     
     alert.addEventListener(CloseEvent.CLOSE, alert_close);
         
     return;
    }    
   }
   private  function alert_close(e:CloseEvent):void{
    focusManager.setFocus(EditAdd1); 
   }