3.29.控制子组件的位置和滚动

<mx:Canvas xmlns:mx="http://www.adobe.com/2006/mxml" width="500"
height="500">
<mx:Script>
<![CDATA[
private var top:TopComponent;
//store the y position
private var topY:Number;
private function showTop():void
{
top = new TopComponent();
addChild(top);
top.verticalScrollPolicy = "none";
top.x = 200;
top.y = 100;
topY = top.y;
top.addEventListener(MouseEvent.MOUSE_DOWN, dragTop);
}
private function dragTop(event:Event):void
{
top.startDrag(false, this.getBounds(stage));
top.addEventListener(MouseEvent.MOUSE_UP,
stopDragTop);
}p
private function stopDragTop(event:Event):void
{
topY = top.y;
top.stopDrag();
top.removeEventListener(MouseEvent.MOUSE_UP,
stopDragTop);
}o
override protected function scrollChildren():void
{
super.scrollChildren();
if(top){
top.y = verticalScrollPosition+topY;
//
top.verticalScrollPosition =
this.verticalScrollPosition/height *
top.height;
}
}

]]>
</mx:Script>
<mx:Panel>
<mx:Label text="LABEL BABEL"/>
<mx:Label text="LABEL BABEL"/>
<mx:Label text="LABEL BABEL"/>
</mx:Panel>
<mx:Panel y="500" height="200">
<mx:Label text="LABEL BABEL"/>
<mx:Label text="LABEL BABEL"/>
<mx:Label text="LABEL BABEL"/>
</mx:Panel>
<mx:Button click="showTop()"/>
</mx:Canvas>