Google image search liked navigation script

This is a script I found, it's a scroll bar script. What I'm thinking is somehow to use mouse wheel to move ScrollDragger and trigger scrollDraggerPress.

I wonder if there is a listener that detect scrollDragger move to a new position and so it call scrollDraggerPress.

Or if there better option for me, please let me know too. thank you

// Scroll My Content function - AS3

function scrollMyContent () {

    // Cache the TextField as a bitmap to improve performance.

    content_mc.cacheAsBitmap = true;

    // Event Listeners

    scrollDragger.addEventListener(MouseEvent.MOUSE_DOWN, scrollDraggerPress);

    stage.addEventListener(MouseEvent.MOUSE_UP, mouseUpOnStage);

    // Set variables

    var scrollbarHeight:Number = scrollbarBG.height;

    var contentHeight:Number = content_mc.height;

    var scrollDraggerHeight:Number = scrollDragger.height;

    var maskHeight:Number = contentMask.height;

    var scrollAmout:Number = (contentHeight-maskHeight)/(scrollbarHeight-scrollDraggerHeight);

    var topBound:Number = scrollbarBG.y;

    var bottomBound:Number = scrollbarBG.height-scrollDraggerHeight+scrollbarBG.y;   

    var startPos:Number = content_mc.y;

    var leftBound:Number = scrollbarBG.x;

    var absNumSet:Number = 0;

    // When scrollDragger gets pressed we do this

    function scrollDraggerPress(event:MouseEvent):void {

        // Set bounds using some of the scroller BG properties claimed above

        var bounds:Rectangle = new Rectangle(leftBound, topBound, 0, bottomBound);

        scrollDragger.startDrag(false, bounds);

        stage.addEventListener(MouseEvent.MOUSE_MOVE, reportStageMouse);

        function reportStageMouse(event:MouseEvent):void {

            absNumSet = Math.abs(scrollbarBG.y - scrollDragger.y);

            content_mc.y = Math.round(absNumSet * - 1 * scrollAmout + startPos);

        }

    }

    // When mouse is released while dragging we do this

    function mouseUpOnStage(event:MouseEvent):void {

        stopDrag();

    }

}

scrollMyContent();