ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Display programming
// This code creates a mouse drag interaction using the startDrag()
// technique.
// square is a MovieClip or Sprite instance).
import flash.events.MouseEvent;
// This function is called when the mouse button is pressed.
function startDragging(event:MouseEvent):void
{
square.startDrag();
}
// This function is called when the mouse button is released.
function stopDragging(event:MouseEvent):void
{
square.stopDrag();
}
square.addEventListener(MouseEvent.MOUSE_DOWN, startDragging);
square.addEventListener(MouseEvent.MOUSE_UP, stopDragging);
This technique suffers from one fairly significant limitation: only one item at a time can be dragged using
startDrag(). If one display object is being dragged and the startDrag() method is called on another display object,
the first display object stops following the mouse immediately. For example, if the startDragging() function is
changed as shown here, only the circle object will be dragged, in spite of the square.startDrag() method call:
function startDragging(event:MouseEvent):void
{
square.startDrag();
circle.startDrag();
}
As a consequence of the fact that only one object can be dragged at a time using startDrag(), the stopDrag()
method can be called on any display object and it stops whatever object is currently being dragged.
If you need to drag more than one display object, or to avoid the possibility of conflicts where more than one object
might potentially use startDrag(), it’s best to use the mouse-following technique to create the dragging effect. With
this technique, when the mouse button is pressed, a function is subscribed as a listener to the mouseMove event of the
Stage. This function, which is then called every time the mouse moves, causes the dragged object to jump to the x, y
coordinate of the mouse. Once the mouse button is released, the function is unsubscribed as a listener, meaning it is
no longer called when the mouse moves and the object stops following the mouse cursor. Here is some code that
demonstrates this technique:
Last updated 6/6/2012
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