flex点击弹出警告

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
<mx:Script>
  <![CDATA[
    import mx.controls.Alert;
    public function addToCart():void
    {
      Alert.show("你确定要退出系统吗?","确认",Alert.YES|Alert.NO,null,null);
    }
  ]]>
</mx:Script>
  <mx:Label text="hello"/>
  <mx:Button label="Add to Cart" click="addToCart()"/>
</mx:Application>

效果如下图所示