Format realtime stopwatch timer to the hundredth using Swift

Question

I have an app using an NSTimer at centisecond (0.01 second) update intervals to display a running stopwatch in String Format as 00:00.00 (mm:ss.SS). (Basically cloning the i

Answer 1

For rapid UI updates you should use a CADisplayLink. Anything faster than the display refresh rate is a waste of processing power since it physically cannot be displayed. It also provides a timestamp of the previous frame so you can try to predict when the next frame will be.

You're calculating CACurrentMediaTime() - timerStarted + elapsedTime multiple times. I would recommend doing it only once and saving it in a local variable.

Consider using NSDateComponentsFormatter. Try to reuse one instance of the formatter rather than creating a new one each time (which is usually the most expensive part). Overall, the less string manipulation you can do, the better.

You can check CACurrentMediaTime at the beginning and end of your display method to see how long it takes. Ideally it should be much less than 16.6ms. Keep an eye on the CPU usage (and general power consumption) in the Xcode debug navigator.