NSTimer 无法正常工作。答案

【问题标题】：NSTimer not working accurately.NSTimer 无法正常工作。
【发布时间】：2015-03-07 05:55:51
【问题描述】：

我正在尝试制作一个倒数计时器，但是我正在为我的代码而苦苦挣扎。我有一个 UIDatePicker 来选择倒计时的日期，但是每次我尝试倒计时时，秒数都从 54 秒开始，而不是调整到设备的实际时间。代码非常简单明了，但我很难弄清楚。

- (IBAction)startCountdown:(id)sender {
if (ti == 0||ti <= 0) {
    [self stopCountdown:self];
}

//Set up a timer that calls the updateTime method every second to update the label
timer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                         target:self
                                       selector:@selector(updateTime)
                                       userInfo:nil
                                        repeats:YES];
}
-(void)updateTime{


//Get the time left until the specified date and convert time into seconds.
NSInteger ti = ((NSInteger)[self.datePicker.date timeIntervalSinceNow]); //this is the key part of the code.
NSInteger seconds = ti % 60;
NSInteger minutes = (ti / 60) % 60;
NSInteger hours = (ti / 3600) % 24;
//NSInteger days = (ti / 86400);

//Update the lable with the remaining time
//self.countdownLabel.text = [NSString stringWithFormat:@"%02i days %02i hrs %02i min %02i sec", days, hours, minutes, seconds];
self.countdownLabel.text = [NSString stringWithFormat:@"%02i hrs %02i min %02i sec", hours, minutes, seconds];

}

请帮帮我，不胜感激！

提前谢谢各位朋友！！

【问题讨论】：

标签： objective-c nstimer countdown uidatepicker nsinteger

【解决方案1】：

有更简单的方法可以提取时间单位，以防止计算错误。看看[NSCalendar components:fromDate:toDate:options:]

它可能变成：

NSDate *now = [NSDate date];
NSCalendar *calendar = [NSCalendar currentCalendar];
NSCalendarUnit components = NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
NSDateComponents *diff = [calendar components:components fromDate:self.datePicker.date toDate:now options:0];
NSInteger seconds = [diff second];
NSInteger minutes = [diff minute];
NSInteger hours = [diff hour];

【讨论】：