isOpaque not stopping passing to parents drawRect

Question

I got a problem with Cocoa and its View redraw hierarchy.

I'm currently testing displaying (audio) levels in a meter style control and I'm using the MeteringView class from MatrixMixerTest example project from apple. This class is drawing the meter and only drawing the difference what got changed which looks like a very efficient class.

My project is splitted into 2 splitviews, in some are NSCollectionViews (Scrollview, Clipview) and in others are only static views. If I add the meter to those "static" views they work fine when these views call setNeedsDisplay:YES. If a meter is added to the view of a CollectionView Item it gets rendered, but loosing its drawn "old level" parts and its corners/background. I think this happens because the CollectionView item gets also called to be redrawn (which has a background image) and everything is gone. It is drawing some parts whats currently changing (the drawing works).

Is there a way to prevent the Item itself to be redrawn? Or, I dont know why it is not happening in those static views, because those views also have background images but do not draw over the meter.

Are there some tricks or whats different in a CollectionView than in a "normal" view?

EDIT: After reading about isOpaque (MeteringView isOpaque = YES) means it should not call the parent views drawRect if set to yes. Well that works for the static views, those MeteringViews do not call parents drawRect, but those in a CollectionView do however. I dont know why.

EDIT 2: I gave this topic another title, because isOpaque=YES in MeteringView is not stopping calling the parents drawRect in a CollectionView, in a normal view it is working. Are there some things to know about? I have to stop redrawing the CollectionView Item because thats the problem.

Thanks in advance guys

Benjamin

Answer 1

isOpaque is just hint to the system. It does not prevent other views from drawing their contents, it only means that it can sometimes skip making other views update their contents.

If your view is opaque, it should draw itself as opaque and completely fill its bounds.