StackOverflow http://stackoverflow.com/a/7059499
Question:I have a UIScrollView that has a series of labels which are rapidly updating numbers (every .06 seconds). While the scroll view is moving, however, the NSTimer is paused and does not continue until after the scrolling and the elastic animation have finished.
How can I avoid this and have the NSTimer run regardless of the state of the scroll view?
Anwser:An easy way to fix this is adding your NSTimer to the mainRunLoop.
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
To remove a timer from all run loop modes on which it is installed, send an invalidate message to the timer.
iOS: UIScrollView pauses NSTimer while scrolling,布布扣,bubuko.com
iOS: UIScrollView pauses NSTimer while scrolling
原文：http://www.cnblogs.com/ihojin/p/scrollview-timer-pause.html