Iphone 倒数计时器不准确

我在我的应用程序中倒数到午夜。唯一的问题是倒计时计时器总是关闭5分钟或更长时间。直到午夜，它才真正接近实际剩下的时间。我做了计算，很确定它是正确的，但也许我犯了一个愚蠢的错误

-(void) timerRun
{
NSDateFormatter *formatterAmPm = [[NSDateFormatter alloc] init];
[formatterAmPm setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterAmPm setDateFormat:@"a"];

NSString *amPmString = [formatterAmPm stringFromDate:[NSDate date]];

secondsCount = secondsCount + 1;
int hours = ((12*3600)-(secondsCount))/3600;
int minutes = ((12*3600)-(secondsCount)-(hours*3600))/60;
int seconds = ((12*3600)-(secondsCount)-(hours*3600))%60;

NSString *timerOutput = [NSString stringWithFormat:@"%.2d:%.2d:%.2d", hours, minutes, seconds];
_countDownLabel.text = timerOutput;

if ((secondsCount == 0) && ([amPmString isEqualToString:@"AM"]))
{
    [_countdownTimer invalidate];
    _countdownTimer = nil;
    MainViewController *ViewController = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
    ViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
    [self.navigationController pushViewController:ViewController animated:YES];
    self.sidePanelController.centerPanel = [[UINavigationController alloc] initWithRootViewController:[[MainViewController alloc] init]];

}
}

-(void) setTimer
{
NSDateFormatter *formatterHour = [[NSDateFormatter alloc] init];
[formatterHour setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterHour setDateFormat:@"HH"];

NSDateFormatter *formatterMinute = [[NSDateFormatter alloc] init];
[formatterMinute setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterMinute setDateFormat:@"mm"];

NSDateFormatter *formatterSecond = [[NSDateFormatter alloc] init];
[formatterSecond setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterSecond setDateFormat:@"ss"];

NSDateFormatter *formatterAmPm = [[NSDateFormatter alloc] init];
[formatterAmPm setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[formatterAmPm setDateFormat:@"a"];

NSString *amPmString = [formatterAmPm stringFromDate:[NSDate date]];
NSString *hourString = [formatterHour stringFromDate:[NSDate date]];
NSString *minuteString = [formatterHour stringFromDate:[NSDate date]];
NSString *secondString = [formatterHour stringFromDate:[NSDate date]];

int hour = (([hourString intValue]) * 60 * 60);
int minute = (([minuteString intValue]) * 60);
int second = [secondString intValue];
if ([amPmString isEqualToString:@"PM"])
{
    stopTime = 12*60*60;
}
else
{
    stopTime = 24*60*60;
}

secondsCount = hour + minute + second;

secondsCount = secondsCount - stopTime;

_countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self     selector:@selector(timerRun) userInfo:nil repeats:YES];
}

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NSTimer

不精确，它会在适当的时间发射。这意味着您不能在尝试时使用它来计算秒数

---

相反，您需要做的是在

timerRun

方法中获取实际时间，并使用该时间确定剩余的秒数。您已经在调用

[NSDate]

来获取AM/PM指示，只需使用它来获取当前时间，然后计算剩余的秒数。

n计时器不是跟踪时间的准确方法，因为它们与运行循环有关。