Question

In Cocoa, when we want to redraw a view, we would send the view a setNeedsDisplay: message telling the view to redraw itself with a parameter of YES. I was wondering if there are any circumstances where you would want to send a view setNeedsDisplay:NO, such as multithreading environments, and if sending a view a setNeedsDisplay:YES, then setting it again immediately after with setNeedsDisplay:NO would make the view redraw itself. If there are no reasons to call setNeedsDisplay:NO, then why create such a tedious method, where they could instead implement something like [view redrawView]

Answer 1

setNeedsDisplay:NO may be used in case you want to discard previously called setNeedsDisplay:YES. E.g. sometimes it is easier to mark all subviews as needing display and then run an algorithm to unmark some of them.