iPhone register for clock updates

Question

A view in my application has a clock that I'd like to keep synced with the system. A number of Stack questions have centred around NSTimer, but before doing that, I want to check if there is a system notification I can register that is fired every minute.

Does such a thing exist? I'm looking through NSNotificationCenter but so far have nothing.

Answer 1

You can use NSTimer's initWithFireDate to fire on the minute by calculating the next change of the minute:

NSDate *currentDate = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"ss"];
int currentTimeSeconds = [dateFormatter stringFromDate:currentDate].intValue;

NSDate *fireDate = [NSDate dateWithTimeIntervalSinceNow:60 - currentTimeSeconds];
NSTimer *updateTimer = [[NSTimer alloc] initWithFireDate:fireDate
                                                 interval:60
                                                   target:self
                                                 selector:@selector(updateSelector)
                                                 userInfo:nil
                                                  repeats:YES];

NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
[runLoop addTimer:updateTimer forMode:NSDefaultRunLoopMode];