Flex 4 List with InteractionMode Touch : how to force a scrollbar visible

I'm using the last Flex 4 sdk Hero. i setup 开发者_JAVA百科a classic List component with InteractionMode="Touch". Thus, my vertical scroll bar is not visible until i drag the list ,which is normal. My customer ask me to add some "page down" button on the list. I've done it as follow, which work perfectly :

private function handleDownButton(event:*):void {



            var currentPosition:Number = wcList.scroller.viewport.verticalScrollPosition;
            var nextPosition:Number = currentPosition+((wcList.dataGroup.layout) as VerticalLayout).getVerticalScrollPositionDelta(NavigationUnit.PAGE_DOWN);

            var anim:Animate = new Animate(wcList.scroller.viewport);
            anim.motionPaths = new <MotionPath>[
                new MotionPath("verticalScrollPosition")];
            anim.motionPaths[0].keyframes = new <Keyframe>[
                new Keyframe(0), new Keyframe(500, nextPosition)];

            anim.play();



            if ((nextPosition+wcList.height)>=wcList.scroller.viewport.contentHeight) {
                buttonDown.enabled=false;
            }
            buttonUp.enabled = true;

        }

My big problem is that my customer also want the vertical scroll bar to be visible during the animation, but i can't find a solution for this (wcList.scroller.verticalScrollBar.visible = true don't work at all).

Any idea of how doing this?

Thanks.

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A hack that might work for you...

http://flexponential.com/2011/06/21/using-drag-and-drop-with-a-spark-list-in-a-mobile-flex-application/