My most recent monkey patch to the Flex framework code took place in the Panel class.  It is possible to drag a Panel completely off the screen, such that the user has no way of dragging it back should they release the mouse button.

Panel has a private handler private function systemManager_mouseMoveHandler (event:MouseEvent) : void that gets called before any mouse event handlers you might listen for should you extend Panel or try any other object oriented approach. There are also two private variables on the Panel class, regX and regY which store the location the mouse was pressed on the Panel’s title bar, and are set in the startDragging() method. (These numbers are useful for determining if the Panel is being dragged off screen as well as for determining where the top-left corner of the Panel is).

I decided to keep it simple and only prevent the user from dragging the Panel off the left or upper edges of the browser. (You can do the same for the bottom and right edges by performing similar calculations… but I didn’t.)

Here’s the code that does the checking (inside systemManager_mouseMoveHandler():

var sx : int = event.stageX;
var sy : int = event.stageY;

var nx : int = event.stageX - regX;
var ny : int = event.stageY - regY;

if (nx < 0 && ny < 0)
  move(0,0);

else if (nx < 0 && ny >= 0)
  move(0, sy-regY);

else if (nx >= 0 && ny < 0)
  move(sx-regX, 0);

else
  move(event.stageX - regX, event.stageY - regY);

Essentially the code detects if the top or left edge of the Panel is in the negative, and if so resets it to zero. There is a stopDragging() method that I originally tried to use in my code, but gave up, because I wanted the user to be able to continue dragging their mouse back onto the browser after they dragged it off.

Adding in the right and bottom will add several more permutations, so I’ve been thinking of more creative ways to handle this, but haven’t got it working the way I want yet. I’ll update this post when I do.