NSDate countdown with NSInterval - iphone

Question

Here's my code:
NSDate *currDate = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
[dateFormatter setDateFormat:#"HH:mm:ss"];
NSString *currentTime = [dateFormatter stringFromDate:currDate];
NSDate *now = [NSDate date];
int interval = 1*60; // one minute (minutes*60)
long int nowSeconds = (long int) [now timeIntervalSince1970];
int secondsLeft = interval - (nowSeconds % interval);
NSDate *nextIntervalDate = [NSDate dateWithTimeIntervalSince1970:nowSeconds+secondsLeft];
NSString *nextTrigger = [dateFormatter stringFromDate:nextIntervalDate];
timeRemaining.text = [NSString stringWithFormat:#"%02d:%02d", secondsLeft/60, secondsLeft%60];
NSLog([NSString stringWithFormat:#"%#:%#", currentTime, nextTrigger]);
if ([currentTime isEqualToString:nextTrigger]) {
}
Problem is, 'if ([currentTime isEqualToString:nextTrigger])' is never equal. Because nextTrigger changes to the next time segment before they're equal. Here is the NSLog:
2013-01-17 15:54:59.987 app[35987:c07] 15:54:59:15:55:00
2013-01-17 15:54:59.997 app[35987:c07] 15:54:59:15:55:00
2013-01-17 15:55:00.007 app[35987:c07] 15:55:00:15:56:00 <----RIGHT HERE
2013-01-17 15:55:00.016 app[35987:c07] 15:55:00:15:56:00
My code's nextTrigger is basically a round up of the current time by the nearest minute. ALSO, this whole code segment is in a repeating NSTimer every .1 seconds.
How can I fix this?

Answer 1

If you have code that you'd like triggered when the next whole minute passes, it's inefficient to repeatedly check to see if said time has passed. Put that code in its own method, and create a single NSTimer to trigger it at the appropriate time.
NSDate* date = [NSDate date] ;
NSCalendar* calendar = [NSCalendar currentCalendar] ;
NSDateComponents* secondsComponents = [calendar components:NSSecondCalendarUnit fromDate:date] ;
NSTimeInterval secondsUntilNextWholeMinute = 60 - secondsComponents.second ;
[NSTimer scheduledTimerWithTimeInterval:secondsUntilNextWholeMinute target:self selector:#selector(yourMethod) userInfo:nil repeats:NO ] ;

Answer 2

I had a somewhat similar problem. What I did was make a copy and check it by that.(one thing is to have both oldTrigger and newTrigger declared already)Check this code
NSDate *currDate = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
[dateFormatter setDateFormat:#"HH:mm:ss"];
NSString *currentTime = [dateFormatter stringFromDate:currDate];
NSDate *now = [NSDate date];
int interval = 1*60; // one minute (minutes*60)
long int nowSeconds = (long int) [now timeIntervalSince1970];
int secondsLeft = interval - (nowSeconds % interval);
NSDate *nextIntervalDate = [NSDate dateWithTimeIntervalSince1970:nowSeconds+secondsLeft];
oldTrigger = nextTrigger;
nextTrigger = [dateFormatter stringFromDate:nextIntervalDate];
timeRemaining.text = [NSString stringWithFormat:#"%02d:%02d", secondsLeft/60, secondsLeft%60];
NSLog([NSString stringWithFormat:#"%#:%#", currentTime, nextTrigger]);
if ([currentTime isEqualToString:oldTrigger]) {
}