<mx:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009"  >

......出现了错误The prefix "mx" for element "mx:WindowedApplication" is not bound.

解决方法：<mx:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009"
      xmlns:s="library://ns.adobe.com/flex/spark"
      xmlns:mx="library://ns.adobe.com/flex/mx" >要补齐。