iphone - NSDateFormatter 返回不正确的字符串？

Question

我在 NSDate 上编写了一个方法作为类别，它从日期返回一个字符串。格式为{四年数}{两个月数}{两天数}。出于某种原因，格式化程序将当前年份作为四位年份数字返回，而不是返回日期的年份。这是我的代码:

- (NSString *) YYYYMMDD{
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];

    [formatter setTimeStyle:NSDateFormatterNoStyle];
    [formatter setDateStyle:NSDateFormatterFullStyle];
    [formatter setDateFormat:@"YYYYMMdd"];   // This line is doing something odd, not sure why yet.

    NSString *dateAsString = [formatter stringFromDate:self];

    NSLog(@"Date: %@ String: %@", [self description], dateAsString);

   return dateAsString;

查看记录的行，您会注意到年份是不灵活的并且坚持当前年份，即使应该由日期对象表示的年份不是当前年份也是如此。

知道这是为什么吗？我使用的格式化程序不正确吗？

Answer 1

如 Data Formatting Guide 中的评论所述:

A common mistake is to use YYYY. yyyy specifies the calendar year whereas YYYY specifies the year (of “Week of Year”), used in the ISO year-week calendar. In most cases, yyyy and YYYY yield the same number, however they may be different. Typically you should use the calendar year.

所以尝试:

[formatter setDateFormat:@"yyyyMMdd"];