flex 让一个容器在另一个容器的内部移动，不会超界

1、主程序源代码如下:

<?xml version="1.0" encoding="utf-8"?>
<s: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"
creationComplete="creationCompleteHandler()">

<fx:Script>
   <![CDATA[
    import flash.geom.Rectangle;
    import mx.core.FlexGlobals;
    import mx.core.UIComponent;
    import mx.events.MoveEvent;
    import mx.managers.PopUpManager;
    import spark.components.TitleWindow;
   
    protected function creationCompleteHandler():void
    {
     var window:TitleWindow = new TitleWindow();
     PopUpManager.addPopUp(window, this, false);
     PopUpManager.centerPopUp(window);
     window.addEventListener(MoveEvent.MOVE, window_moveHandler);
    }
   
    protected function window_moveHandler(event:MoveEvent):void
    {
     var window:UIComponent = event.currentTarget as UIComponent;
     var application:UIComponent = FlexGlobals.topLevelApplication as UIComponent;
     var bounds:Rectangle = new Rectangle(0, 0, application.width, application.height);
     var windowBounds:Rectangle = window.getBounds(application);
     var x:Number;
     var y:Number;
     if (windowBounds.left <= bounds.left)
      x = bounds.left;
     else if (windowBounds.right >= bounds.right)
      x = bounds.right - window.width;
     else
      x = window.x;
     if (windowBounds.top <= bounds.top)
      y = bounds.top;
     else if (windowBounds.bottom >= bounds.bottom)
      y = bounds.bottom - window.height;
     else
      y = window.y;
     window.move(x, y);
    }
   
   ]]>
</fx:Script>

</s:WindowedApplication>