ios - 45 分钟后计时器不会停止

Question

我有一个 NSTimer，我希望它在 45 分钟后停止，但它不会停止。我做错了什么？

TIMER_COUNT = 45

HOURS_IN_HOURS = 60

HOURS_IN_DAY = 24

- (void)start
{
    self.timerCountdown = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateCountdown) userInfo:nil repeats: YES];
}

- (void)stop
{
    [self.timerCountdown invalidate];
    self.timerCountdown = nil;
}

- (void)updateCountdown
{
    NSDate *currentDate = [NSDate date];
    NSDate *finalTime = [currentDate dateByAddingTimeInterval:(TIMER_COUNT * HOURS_IN_HOUR)];

    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSDateComponents *componentsHours   = [calendar components:NSHourCalendarUnit fromDate:currentDate];
    NSDateComponents *componentMinuts   = [calendar components:NSMinuteCalendarUnit fromDate:currentDate];
    NSDateComponents *componentSeconds  = [calendar components:NSSecondCalendarUnit fromDate:currentDate];

    NSCalendar *gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *componentsDaysDiff = [gregorianCalendar components:NSDayCalendarUnit
                                                                fromDate:currentDate
                                                                  toDate:finalTime
                                                                 options:0];

    NSLog(@"%20d Days, %02d Hours, %02d Minutes, %02d Seconds.", componentsDaysDiff.day, HOURS_IN_DAY - componentsHours.hour, HOURS_IN_HOUR - componentMinuts.minute, HOURS_IN_HOUR - componentSeconds.second);

    if ([currentDate compare:finalTime] == NSOrderedSame)
    {
        NSLog(@"Done.");
        [self stop];
    }
}

提前致谢。

Answer 1

因为您的 currentDate 会在您的计时器每次计时时保持设置。每次 updateCountdown 方法运行时，[NSDate date] 都会将 currentDate 设置为当前时间。因此 finalTime 总是比 currentDate 早 45 分钟。您应该创建一个 startDate 属性并将其设置在 start 方法中:

- (void)start
{
    self.timerCountdown = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateCountdown) userInfo:nil repeats: YES];
    self.startDate = [NSDate date];
}

然后检查 updateCountdown 方法中的属性:

if ([self.startDate compare:finalTime] == NSOrderedSame)
{
    NSLog(@"Done.");
    [self stop];
}

或者，您可以使用一个整数来表示您期望的滴答数，然后每次计时器滴答时从该整数中减去一个。像这样:

- (void)start
{
    self.timerCountdown = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateCountdown) userInfo:nil repeats:YES];
    self.countdown = TIMER_COUNT * HOURS_IN_HOUR;
}

- (void)updateCountdown
{
    self.countdown--;

    //your code

    if (self.countdown == 0)
    {
         NSLog(@"Done.");
         [self stop];
    }
}