flex中viewstack

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
  <mx:ViewStack x="0" y="0" id="viewstack1" width="619" height="700">
    <mx:Canvas id="View1" width="100%" height="100%">
        <mx:Button label="View2 " click="viewstack1.selectedChild=View2" x="322" y="322"/>
      </mx:Canvas>
   <mx:Canvas id="View2" width="100%" height="100%" color="#3FCFE9">
     <mx:Label id="greet" text="哈哈" fontSize="16" color="#FF0000" x="308" y="229">
    </mx:Label>
  </mx:Canvas>
 </mx:ViewStack>
</mx:Application>