计算某个时间和当前时间的时间差

NSString *timeStr = @"2019-06-28 12:12:12";

// 1.将时间转换为date

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

formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss";

NSDate *date1=[NSDate date];

NSDate *date2 = [formatter dateFromString:timeStr];

// 2.创建日历

NSCalendar *calendar = [NSCalendar currentCalendar];

NSCalendarUnit type = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;

// 3.利用日历对象比较两个时间的差值

NSDateComponents *cmps = [calendar components:type fromDate:date1 toDate:date2 options:0];

// 4.输出结果

NSLog(@"时间差%ld年%ld月%ld日%ld小时%ld分钟%ld秒", cmps.year, cmps.month, cmps.day, cmps.hour, cmps.minute, cmps.second);