Called when mousewheel is spun while the mouse pointer is over the frame. If a frame does not have an OnMouseWheel handler, the event is passed on to underlying frames.
- arg1 - Number indicating the direction the wheel is spinning
- 1 for spinning up
- -1 for spinning down
- (i.e. you will want to use (-arg1) for offsetting the position in a list view)
If a frame did not previously have an <OnMouseWheel> tag, which will always be the case for CreateFrame()ed frames, you need to do Frame:EnableMouseWheel(1) on it in order to receive this event.