Problems replicating drag-and-drop with mouse even

Question

I want to replicate the standard startDrag/stopDrag events with my own routine to alter things a bit, and I run into some kind of event propagation or bubbling problem. Here is my code:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute"
                mouseDown="mouseDown = true" mouseUp="mouseDown = false"
                mouseMove="mouseMove(event)">

  <mx:Script>
    <![CDATA[
        private var mouseDown:Boolean = false;
        private var oldMouseX:int = 0, oldMouseY:int = 0;

        private function mouseMove(e:MouseEvent):void {
            if (mouseDown) {
                object.x += (e.localX - oldMouseX);
                object.y += (e.localY - oldMouseY);
            }

            oldMouseX = e.localX;
            oldMouseY = e.localY;

            trace(e.localX);
        }
    ]]>
  </mx:Script>  

  <mx:Label id="object" text="Drag me" />

</mx:Application>

The problem with this code is that as you drag the object to the right, you will see in the trace that occasionally some random localX values arrive there, resulting in the object jerking from side to side.

I don't understand how to fix that part, I do think it's the label which bubbles the mousemove event, but I don't understand how to stop it from doing that.
Any suggestions are greatly appreciated!

Answer 1

Track which target you're concerned about and only listen to events directly from it. So in your mousemove function, check e.target == your object. In this case, the application. You will get stray events bubbling from sub components.

    public static function smoothDrag(pressEvent:MouseEvent, dragTarget:DisplayObject = null, done:Function=null, move:Function = null, parent:DisplayObject = null):void {
        var target:DisplayObject = dragTarget;
        parent = parent || target.parent;
        var eventParent:EventDispatcher = target.stage || parent;

        var moveFunc:Function = move;
        var doneFunc:Function = done;

        var startPoint:Point = MouseHelpers.pointTo(pressEvent.localX, pressEvent.localY, pressEvent.target as DisplayObject, parent);
        startPoint.x -= target.x
        startPoint.y -= target.y;

        var setPosition:Function = function(e:MouseEvent):void 
        {
            e.stopImmediatePropagation();
            var p:Point = MouseHelpers.pointTo(e.localX,e.localY, e.target as DisplayObject, parent);
            target.x = p.x - startPoint.x;
            target.y = p.y - startPoint.y;

            if (moveFunc != null) {
                moveFunc();
            }
        }

        var stopMove:Function = function(e:MouseEvent):void {
            e.stopImmediatePropagation();
            eventParent.removeEventListener(MouseEvent.MOUSE_MOVE, setPosition, true);
            eventParent.removeEventListener(MouseEvent.MOUSE_UP, stopMove, true);
            eventParent.removeEventListener(MouseEvent.ROLL_OVER, EventHelpers.stop, true);
            eventParent.removeEventListener(MouseEvent.MOUSE_OVER, EventHelpers.stop, true);

            if (doneFunc != null) {
                doneFunc(e);
            }
        }
        eventParent.addEventListener(MouseEvent.ROLL_OVER, EventHelpers.stop, true, 0, true);
        eventParent.addEventListener(MouseEvent.MOUSE_OVER, EventHelpers.stop, true, 0, true);
        eventParent.addEventListener(MouseEvent.MOUSE_MOVE, setPosition, true, 0, true);
        eventParent.addEventListener(MouseEvent.MOUSE_UP, stopMove, true, 0, true);
    }


    /**
     *  Translate a point from one object's reference into another. Best used when you have a descendant object x/y and you
     *  want to get that position relative to an ancestor. Uses the localToGlobal/globalToLocal style. 
     **/
    public static function pointTo(fromX:Number, fromY:Number, src:DisplayObject, dest:DisplayObject):Point {
        var p:Point = new Point(fromX, fromY);
        if(src != dest) {
            p = src.localToGlobal(p);
            p = dest.globalToLocal(p);
        }
        return p;
    }