setNeedsDisplayInRect: causes the whole view to be updated

Question

I\'m working on a painting app that uses CoreGraphics for rendering. My problem is, for performance, I am trying to limit the updates to only certain portions of the view th

Answer 1

Check this apple document

they said :

because of the way that iPhone/iPod touch/iPad updates its screen, the entire view will be redrawn if you call -setNeedsDisplayInRect: or -setNeedsDisplay:.

Also

Each UIView is treated as a single element. When you request a redraw, in part or whole, by calling -setNeedsDisplayInRect: or -setNeedsDisplay:, the entire view will be marked for updates.

so I think you need to use subviews to update independent rect of the whole View.