Have an 'invisible' rectangle that sitsover the object and extends beyond the visible area. Use that for collision detection - you will detect the collision before the object looks like it's colliding. You can then adjust the x,y position of the object to be further away from the object with which the collision is immenent.
howo to adjust x,y position? This is really my problem.
Suppose the fix item bounds is fixBound = new Rectangle(x1,y1,w1,h1); the moving item bounds is movingBound = new Rectangle(x2,y2,w2,h2); the moving item moved offsetPoint is offset = new Point(x,y);
A simple approach to this is to remember the x and y co-ordinate of the item being dragged. So on start drag, record the x,y position. whenever you receive a move or drag end event, check for a collision. If there's a collision, reset the position of the item to the last recorded position. If there's no collision, you can record the update x, y co-ordinates and continue.
This will stop anyone dragging an item over a dodgy object.
Googling " as3 collision avoidance" may help.