Question

I’m relatively new to coding, and wondering if there’s a conventional way to have some code execute on every nth iteration of a loop (in this case, an NSTimer ticking).

I’m using a CADisplayLink and it updates however many times per second, 40, 50, whatever. If I want to execute some code on every, say, 500 of those loops, is there a standard way to do so? I assume I could put something together with the modulo operator and an integer, but is there a better / more normalized way that a new coder should know?

Extra clarity (though I’m sure this is a fairly common thing to do..): I have a timer that ticks 60 times per second, but I only want to do something with every 10th iteration. I already know that I can use a modulo and an integer to do this, but I want to know if there’s any other convention for handling a situation like this.

Thanks in advance!

Answer 1

Establish a dedicated timer for the right interval.

Regardless of whether you’re using NSTimer or CADisplayLink, timer calls can be coalesced and offset if they take too long. If you have a display link that takes 20 frames to run, it only gets called thrice every second (given the refresh interval is 60 frames per second). And if you have a timer set to run every second that at one instance takes a bit more than two and a half seconds to run, it will have “ate” its next iteration and will run the next iteration half a second too late.

Because of this, your timer can get out of sync if you only count timer calls. To do something repeatedly on an interval, having a timer set to that interval is the absolute best approximation.

Having a second timer like this is not a performance problem unless you do very many timers, in which case you should standardize on one tick timer and have events scheduled for specific points in time (which still isn’t the same as counting previous iterations).