iOS Countdown Timer To Specific Date

Question

I am trying to get a countdown timer to a specific date. I use:

-(void) viewWillAppear:(BOOL)animated {

    NSString *str =@"12/27/2013";
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    [formatter setDateFormat:@"MM/dd/yyyy"];
    NSDate *date = [formatter dateFromString:str];

    NSTimeInterval numberOfSecondsUntilSelectedDate = [date timeIntervalSinceNow];
    NSInteger numberOfDays = numberOfSecondsUntilSelectedDate / 86400;


    startTime = [[NSDate date] retain];

    secondsLeft = numberOfDays;
    NSLog(@"number%f", numberOfSecondsUntilSelectedDate);
    [self countdownTimer];

}
- (void)updateCounter:(NSTimer *)theTimer {
    if(secondsLeft > 0 ){
        secondsLeft -- ;
        days = secondsLeft / 86400;
        NSLog(@"%d", days);
        hours = secondsLeft / 3600;
        minutes = (secondsLeft % 3600) / 60;
        seconds = (secondsLeft %3600) % 60;
        myCounterLabel.text = [NSString stringWithFormat:@"%02d Days %02d Hours %02d Minutes %02d Seconds", days, hours, minutes, seconds];
    }
    else{
        secondsLeft = 16925;
    }
}

-(void)countdownTimer{

    secondsLeft = hours = minutes = seconds = 0;
    if([timer isValid])
    {
        [timer release];
    }
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(updateCounter:) userInfo:nil repeats:YES];
    [pool release];
}

However, the day keeps coming out as 0. What am I doing wrong?

Answer 1

The way to count down to a particular date is to just start a timer and ask each time it fires whether that date has come to pass. The second problem is how to calculate the hours minutes seconds until that time for the UI. The answer there is NSDateFormatter -- definitely not *60 or *24 math.

@property (strong, nonatomic) NSDate *targetDate;

// compute targetDate as you have it

// ...
self.targetDate = [formatter dateFromString:str]

// start a timer
[NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(updateCounter:) userInfo:nil repeats:YES]; 

- (void)updateCounter:(NSTimer *)theTimer {

    NSDate *now = [NSDate date]; 
    // has the target time passed?
    if ([self.targetDate earlierDate:now] == self.targetDate) {
        [theTimer invalidate];
    } else {
        NSUInteger flags = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
        NSDateComponents *components = [[NSCalendar currentCalendar] components:flags fromDate:now toDate:self.targetDate options:0];

        NSLog(@"there are %ld hours, %ld minutes and %ld seconds remaining", (long)[components hour], (long)[components minute], (long)[components second]);
    }
}

Answer 2

Logic error....

-(void) viewWillAppear:(BOOL)animated {

    NSString *str =@"12/27/2013";
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    [formatter setDateFormat:@"MM/dd/yyyy"];
    NSDate *date = [formatter dateFromString:str];

    NSTimeInterval numberOfSecondsUntilSelectedDate = [date timeIntervalSinceNow];
    NSInteger numberOfDays = numberOfSecondsUntilSelectedDate / 86400;


    startTime = [[NSDate date] retain];

    secondsLeft = numberOfSecondsUntilSelectedDate;
    NSLog(@"number%f", numberOfSecondsUntilSelectedDate);
    [self countdownTimer];

}