FLEX 获得子窗口popupWindow的属性值

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml?" layout="absolute">
?<mx:Panel x="94" y="178" width="503" height="347" layout="absolute">
? <mx:TextInput x="134" y="64" id="tit_usr" text="username"/>
? <mx:TextInput x="134" y="125" id="tit_psw" text="password"/>
? <mx:Button x="171" y="209" label="Submit" click="mytw_click()"/>
?</mx:Panel>
?<mx:Script>
? <![CDATA[
?import mx.containers.TitleWindow;
?import mx.managers.PopUpManager;
?import mx.controls.Text;
?
?private var tw:titlewindow=new titlewindow();
?
?private function? mytw_click():void{
? if(tw.visible){
?? PopUpManager.removePopUp(tw);
? }
? PopUpManager.addPopUp(tw,this);
? PopUpManager.centerPopUp(tw);
? tw.addEventListener("tw_click",update);
?}
?
?private function update(event:Event):void{
? tit_usr.text=tw.tw_usr.text;
? tit_psw.text=tw.tw_psw.text;
? PopUpManager.removePopUp(tw);
?}
? ]]>
?</mx:Script>
?
</mx:Application>

弹出窗口：

<mx:TitleWindow xmlns:mx="http://www.adobe.com/2006/mxml?" layout="absolute" width="498" height="368" showCloseButton="true" close="PopUpManager.removePopUp(this)"> ?<mx:Label x="96" y="67" text="username" width="97" height="26"/> ?<mx:Label x="96" y="128" text="password" width="97" height="24"/> ?<mx:TextInput x="217" y="65" id="tw_usr"/> ?<mx:TextInput x="217" y="126" id="tw_psw"/> ?<mx:Button x="228" y="239" label="Click" click="btn_click()"/> ?<mx:Script> ? <![CDATA[ ?import mx.managers.PopUpManager; ?import mx.controls.Text; ? ?private function btn_click():void{ ? dispatchEvent(new Event("tw_click")); ?} ? ]]> ?</mx:Script> ? </mx:TitleWindow>