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">

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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;  

}