The original question............................................... If you are an advanced user of drawRect on your ipop*, you will know that of course drawRect will not actually run until "all processing is finished." setNeedsDisplay flags a view as invalidated and the OS, in a word, waits until all processing is done. This can be infuriating in the common situation where you want to have: a view controller 1 starts some function 2 which incrementally 3 creates a more and more complicated artwork and 4 at each step, you setNeedsDisplay (wrong!) 5 until all the work is done 6 Of course, when you do that, all that happens is that drawRect is run once only after step 6. What you want is for the ^&£@%$@ view to be refreshed at point 5. This can lead to you smashing your ipops on the floor, scanning Stackoverflow for hours, screaming at the kids more than necessary about the dangers of crossing the street, etc etc. What