ios - 为什么 [日历 dateFromComponents :] always return hour 16 ?

Question

当我将 [NSDate date] 传递给 NSDateComponents ，然后在修改工作日后传回时，我总是得到时间 16:00:00 。为什么？

代码如下:

     {
        NSCalendar *calendar = [[NSCalendar alloc]initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
        NSDate *now = [NSDate date];
        NSLog(@"now = %@",now);

        NSDateComponents *firstDayOfWeek = [calendar components:NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekday fromDate:now];
        firstDayOfWeek.weekday = 1; // Monday as first day of week

        NSDate *firstDayOfWeekDate = [calendar dateFromComponents:firstDayOfWeek];
        NSLog(@"first day = %@", firstDayOfWeekDate);
    }

    {
        NSCalendar *calendar = [[NSCalendar alloc]initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
        NSDate *now = [NSDate date];
        NSLog(@"now = %@",now);

        NSDateComponents *firstDayOfWeek = [calendar components:NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekday | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond fromDate:now];
        firstDayOfWeek.weekday = 1; // Monday as first day of week
        firstDayOfWeek.hour = 1;
        firstDayOfWeek.minute = 1;
        firstDayOfWeek.second = 1;

        NSDate *firstDayOfWeekDate = [calendar dateFromComponents:firstDayOfWeek];
        NSLog(@"first day = %@", firstDayOfWeekDate);
    }

输出是:

 now = 2016-01-18 03:14:08 +0000
 first day = 2016-01-17 16:00:00 +0000
 now = 2016-01-18 03:14:08 +0000
 first day = 2016-01-17 17:01:01 +0000

为什么小时从 16 开始？

Answer 1

NSDateComponents 没有到达 16:00:00。现在是您当前时区的午夜。但是 NSLog 显示的是等效的 GMT 时间。这就是 +0000 的意思:例如格林威治标准时间 +00:00。

最重要的是，如果您想在本地时区查看生成的 NSDate 对象，您应该使用 NSDateFormatter。