Determining if the scroll bars are visible in a Spark Scroller container in Flex 4

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2010/04/30/determining-if-the-scroll-bars-are-visible-in-a-spark-scroller-container-in-flex-4/ -->
<s:Application name="Spark_Scroller_verticalScrollBar_visible_test"
        xmlns:fx="http://ns.adobe.com/mxml/2009"
        xmlns:s="library://ns.adobe.com/flex/spark"
        xmlns:mx="library://ns.adobe.com/flex/mx">
    <s:controlBarContent>
        <mx:Form>
            <mx:FormItem label="width:">
                <s:HSlider id="wSl"
                        minimum="100" maximum="400"
                        value="100"
                        change="wSl_changeHandler(event);"
                        changeEnd="wSl_changeHandler(event);" />
            </mx:FormItem>
            <mx:FormItem label="height:">
                <s:HSlider id="hSl"
                        minimum="100" maximum="300"
                        value="100"
                        change="hSl_changeHandler(event);"
                        changeEnd="hSl_changeHandler(event);" />
            </mx:FormItem>
        </mx:Form>
    </s:controlBarContent>
 
    <fx:Script>
        <![CDATA[
            protected function wSl_changeHandler(evt:Event):void {
                horFrmItm.required = scr.horizontalScrollBar.visible;
            }
 
            protected function hSl_changeHandler(evt:Event):void {
                verFrmItm.required = scr.verticalScrollBar.visible;
            }
        ]]>
    </fx:Script>
 
    <s:Panel horizontalCenter="0" verticalCenter="0">
        <s:controlBarContent>
            <mx:Form paddingTop="0" paddingBottom="0">
                <mx:FormItem id="horFrmItm" label="horizontal scroll bar visible:" />
                <mx:FormItem id="verFrmItm" label="vertical scroll bar visible:" />
            </mx:Form>
        </s:controlBarContent>
        <s:Scroller id="scr"
                width="300" height="160">
            <s:Group>
                <s:Rect id="rect"
                        width="{wSl.value}" height="{hSl.value}">
                    <s:fill>
                        <s:LinearGradient rotation="45">
                            <s:GradientEntry color="haloGreen" />
                            <s:GradientEntry color="haloBlue" />
                        </s:LinearGradient>
                    </s:fill>
                </s:Rect>
            </s:Group>
        </s:Scroller>
    </s:Panel>
 
</s:Application>