Is it possible to observe -visibleRect

Question

I would like to be notified whenever a certain NSView's - (NSRect)visibleRect changes because I want to do some fancy subview layout based on the visible rect. Frankly, right now I'm stumped; -visibleRect doesn't emit KVO notifications (which makes sense), and there doesn't seem to be way to find out if the visible rect changed or not without explicitly calling -visibleRect.

Is this at all possible? (or is it a terrible, terrible idea?)

Answer 1

I think you can either override -[NSView updateTrackingAreas] or listen for NSViewDidUpdateTrackingAreasNotification. Those may happen on more occasions than just a change of the visible rect, but they should happen for any change of the visible rect. I think.

That said, it may be a terrible idea. Hard to know. :)

Answer 2

Another option post 10.5 is the -viewWillDraw method which is called just prior to the view (and its subviews) being drawn. You can fetch the view's visible rectangle and perform layout prior to calling [super viewWillDraw].