flex 控制弹出窗口的移动范围

<s:TitleWindow 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="700" height="620" windowMove="windowMoveHandler(event)"
creationComplete="titlewindow1_creationCompleteHandler(event)" fontSize="12">

protected function windowMoveHandler(event:TitleWindowBoundsEvent):void
{
event.target.x = event.target.x < 0 ? 0 : event.target.x;
event.target.x =(event.target.x + event.target.width > event.target.parent.width) ?
(event.target.parent.width - event.target.width) : event.target.x;
event.target.y = event.target.y < 0 ? 0 : event.target.y;
event.target.y = (event.target.y + event.target.height > event.target.parent.height) ?
event.target.parent.height - event.target.height : event.target.y;

}