计算给定时间与现在的时间差

- (void)timerFireMethod:(NSTimer *)timer

{

    NSCalendar *calendar = [NSCalendar currentCalendar];

    

    // 目标时间

    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    NSDate *fireDate = [dateFormatter dateFromString:self.endtime];

    

    NSDate *today = [NSDate date];//当前时间

    

    unsigned int unitFlags = NSCalendarUnitDay | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;

    NSDateComponents *d = [calendar components:unitFlags fromDate:today toDate:fireDate options:0];//计算时间差

    

    NSString *day = [d day] > 0 ? [NSString stringWithFormat:@"%zd天", [d day]] : @"";

    NSString *hour = [d hour] > 0 ? [NSString stringWithFormat:@"%zd小时", [d hour]] : @"";

    NSString *minute = [d minute] > 0 ? [NSString stringWithFormat:@"%zd分", [d minute]] : @"";

    NSString *second = [d second] > 0 ? [NSString stringWithFormat:@"%zd秒", [d second]] : @"";

    

    self.calendar.text = [NSString stringWithFormat:@"%@%@%@%@后截止", day, hour, minute, second];//倒计时显示

    if([d day]<0 || [d hour]<0 || [d minute]<0 || [d second]<0) {

        self.calendar.text = @"已结束";

    }

}