What is the real difference between UIView methods setNeedsLayout and setNeedsDisplay?
As usual documentation is foggy about this.
Actually the documentation is pretty clear about this:
setNeedsLayout will layout subviews
Call this method on your application’s main thread when you want to adjust the layout of a view’s subviews.
setNeedsDisplay will call for a redraw of your view (
drawRect:, etc).You can use this method or the setNeedsDisplayInRect: to notify the system that your view’s contents need to be redrawn.
来源：https://stackoverflow.com/questions/14506968/setneedslayout-and-setneedsdisplay