Flex初学之键盘监听失效

最近开始学Flex,一来就遇到了问题，KeyBoardEvent无法生效，情景如下

 

<?xml version="1.0" encoding="utf-8"?><s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"   xmlns:s="library://ns.adobe.com/flex/spark"   xmlns:mx="library://ns.adobe.com/flex/mx"   width="720" minWidth="720" minHeight="600" backgroundColor="#FFFFFF"   preloaderChromeColor="#FFFFFF" creationComplete="init()"><s:layout><s:BasicLayout/></s:layout><fx:Declarations></fx:Declarations><fx:Script><![CDATA[public function init():void{this.addEventListener(KeyboardEvent.KEY_DOWN,onKeyDown);}private function onKeyDown(e:KeyboardEvent):void{trace(e.keyCode);}]]></fx:Script></s:Application>

 

原因是因为程序没有获得焦点，加上this.setFocus(); 即可解决