Reset an NSTimer's firing time to be from now instead of the last fire

Question

I have a NSTimer that fires with an interval of 3 seconds to decrease a value. When I do an action that increases that value, I want to restart the timer to cou

Answer 1

I've done a little testing, and it turns out that resetting the fireDate is about four times faster than invalidating and re-creating the timer. First, I create a timer which calls the method doNothing:

if (!testTimer) {
    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:3.0
                                                      target:self
                                                    selector:@selector(doNothing:)
                                                    userInfo:nil
                                                     repeats:NO];
    testTimer   = timer;
}

Here is the test code:

- (void) testInvalidatingTimer {
    for (int n = 0; n < 10000; n++) {
        [testTimer invalidate];
        testTimer = nil;

        NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:3.0
                                                          target:self
                                                        selector:@selector(doNothing:)
                                                        userInfo:nil
                                                         repeats:NO];
        testTimer   = timer;
    }
}

- (void) testResettingTimer {
    for (int n = 0; n < 10000; n++) {
        if ([testTimer isValid]) {
            testTimer.fireDate = [NSDate dateWithTimeIntervalSinceNow:3.0];
        }
    }
}

Running that on an iPad Air yields 0.198173 s for invalidatingTimer and 0.044207 s for resettingTimer. If performance is your target, I recommend to reset the fireDate. It is also quite a bit less coding effort.