flex 利用hslider控件以容器中心放缩图片

请问大家  有一图片在一容器中（canvas或 vbox）我想以容器为中心利用hslider控件来放缩图片，，该如何实现呢?在线等答案!!!

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XML code:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical">

<mx:Script>
<![CDATA[
import flash.events.Event;
import mx.controls.sliderClasses.Slider;

private var actualWidth:Number = 0;
private var actualHeight:Number = 0;

private function center(flag:Boolean = false):void
{
if (flag)
{
actualWidth = image.contentWidth;
actualHeight = image.contentHeight;
}
image.move(Math.round((canvas.width - image.contentWidth) / 2),
Math.round((canvas.height - image.contentHeight) / 2));
}

private function sliderChangeHandler(event:Event):void
{
var value:Number = (event.target as Slider).value;
image.content.width = Math.round(actualWidth * value);
image.content.height = Math.round(actualHeight * value);
center();
}
]]>