NSTimer is very useful to do something repeatedly for some period of time.
// Method for timer to callback.
- (void) handleTimer: (NSTimer *) timer
{
// Your work here (periodic work)
}
// Create a NSTimer object to call above callback method.
//
NSTimer *timer;
timer = [NSTimer scheduledTimerWithTimeInterval: 0.03f target: self selector: @selector(handleTimer:)
userInfo: nil repeats: YES];
// Dismiss timer when you are done with it.
//
[tmier invalidate];