How to force a UIView to redraw: setNeedsDisplay()
All views and subclasses are rendered using the drawRect() method, but you should never call that method directly yourself. Instead, it gets called by the system whenever drawing is required, which allows it to to avoid multiple redraws if drawRect() is called several times in a row.
Instead, if you want a view to redraw immediately, you should call its setNeedsDisplay() method like this:
myButton.setNeedsDisplay()That will ask UIKit to redraw the button using drawRect(), but only if a redraw is not already queued.
Available from iOS 2.0
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