Question

当我将[NSDate日期]传递给NSDateComponents，然后在工作日修改后传回，我总是得到16:00:00。为什么？

以下代码：

     {
        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

这是由于时区。

尝试在使用NSDateFormatter输出日期之前添加NSLog，例如

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setLocale:[NSLocale currentLocale]];
[dateFormatter setDateStyle:NSDateFormatterShortStyle];
[dateFormatter setTimeStyle:NSDateFormatterLongStyle];
NSString *dateDisplay = [dateFormatter stringFromDate:firstDayOfWeekDate];
NSLog(@"first day = %@",dateDisplay);

您可以参考this article了解更多示例。

Answer 2

NSDateComponents没有将其16:00:00。它正在你当前时区的午夜。但NSLog向您显示相当的GMT时间。这就是+0000的含义：例如GMT +00：00。

底线，如果您想在当地时区看到生成的NSDate对象，则应使用NSDateFormatter。

为什么[calendar dateFromComponents：]总是返回16小时？

2 个答案: