在iOS 3.0中,NSDateFormatter为@"dd-MM-yy"返回nil

Question

我有这部分代码:

NSDate *date =nil;
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
[dateFormatter setDateFormat:@"dd-MM-yy"];
date = [dateFormatter dateFromString:inString];
[dateFormatter release];

它在iOS 4.0中的预期效果非常好.但是相同的代码在3.0中没有.

我得到的字符串就像"12-Nov-10",它包含在inString指针中.

如果本机操作系统是3.0或3.1,则日期格式化程序返回nil.出于某些原因,我需要坚持使用相同的日期格式.还有其他人遇到过这个问题吗？有什么建议来解决这个问题吗？

谢谢,

拉吉

编辑: 正确的代码,遵循Harkonian指出的建议和问答讨论:

NSDate *date =nil;
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
[dateFormatter setDateFormat:@"dd-MMM-yy"];

NSLocale *enUSPOSIXLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
[dateFormatter setLocale:enUSPOSIXLocale];
[enUSPOSIXLocale release];

date = [dateFormatter dateFromString:inString];
[dateFormatter release];

Answer 1

一个非常有用的页面不再存在,所以只需将其内容放在此处用于存档目的:

a:  AM/PM
A:  0~86399999 (Millisecond of Day)

c/cc:   1~7 (Day of Week)
ccc:    Sun/Mon/Tue/Wed/Thu/Fri/Sat
cccc:   Sunday/Monday/Tuesday/Wednesday/Thursday/Friday/Saturday

d:  1~31 (0 padded Day of Month)
D:  1~366 (0 padded Day of Year)

e:  1~7 (0 padded Day of Week)
E~EEE:  Sun/Mon/Tue/Wed/Thu/Fri/Sat
EEEE:   Sunday/Monday/Tuesday/Wednesday/Thursday/Friday/Saturday

F:  1~5 (0 padded Week of Month, first day of week = Monday)

g:  Julian Day Number (number of days since 4713 BC January 1)
G~GGG:  BC/AD (Era Designator Abbreviated)
GGGG:   Before Christ/Anno Domini

h:  1~12 (0 padded Hour (12hr))
H:  0~23 (0 padded Hour (24hr))

k:  1~24 (0 padded Hour (24hr)
K:  0~11 (0 padded Hour (12hr))

L/LL:   1~12 (0 padded Month)
LLL:    Jan/Feb/Mar/Apr/May/Jun/Jul/Aug/Sep/Oct/Nov/Dec
LLLL:   January/February/March/April/May/June/July/August/September/October/November/December

m:  0~59 (0 padded Minute)
M/MM:   1~12 (0 padded Month)
MMM:    Jan/Feb/Mar/Apr/May/Jun/Jul/Aug/Sep/Oct/Nov/Dec
MMMM:   January/February/March/April/May/June/July/August/September/October/November/December

q/qq:   1~4 (0 padded Quarter)
qqq:    Q1/Q2/Q3/Q4
qqqq:   1st quarter/2nd quarter/3rd quarter/4th quarter
Q/QQ:   1~4 (0 padded Quarter)
QQQ:    Q1/Q2/Q3/Q4
QQQQ:   1st quarter/2nd quarter/3rd quarter/4th quarter

s:  0~59 (0 padded Second)
S:  (rounded Sub-Second)

u:  (0 padded Year)

v~vvv:  (General GMT Timezone Abbreviation)
vvvv:   (General GMT Timezone Name)

w:  1~53 (0 padded Week of Year, 1st day of week = Sunday, NB: 1st week of year starts from the last Sunday of last year)
W:  1~5 (0 padded Week of Month, 1st day of week = Sunday)

y/yyyy: (Full Year)
yy/yyy: (2 Digits Year)
Y/YYYY: (Full Year, starting from the Sunday of the 1st week of year)
YY/YYY: (2 Digits Year, starting from the Sunday of the 1st week of year)

z~zzz:  (Specific GMT Timezone Abbreviation)
zzzz:   (Specific GMT Timezone Name)
Z:  +0000 (RFC 822 Timezone)

Answer 2

如果您使用的是用户可见日期,则应避免设置日期格式字符串,因为很难预测格式字符串在所有可能的用户配置中的表达方式.相反,你应该尝试限制自己设置日期和时间样式(通过 - [NSDateFormatter setDateStyle:]和 - [NSDateFormatter setTimeStyle:]).

另一方面,如果您使用的是固定格式的日期,则应首先将日期格式化程序的区域设置设置为适合您的固定格式的区域设置.在大多数情况下,选择的最佳语言环境是"en_US_POSIX",这是一种专门用于产生美国英语结果的语言环境,无论用户和系统偏好如何."en_US_POSIX"在时间上也是不变的(如果美国在未来的某个时刻改变了格式化日期的方式,"en_US"将改变以反映新行为,但"en_US_POSIX"将不会),以及机器之间( "en_US_POSIX"在iPhone OS上的工作方式与在Mac OS X上的工作方式相同,就像在其他平台上一样.

将"en_US_POSIX"设置为日期格式化程序的语言环境后,您可以设置日期格式字符串,日期格式化程序将对所有用户表现一致.

以上信息和更多内容可以在Apple的技术问答QA1480中找到

这是我的应用程序中的一段代码,它实现了上述建议:

static NSDateFormatter* dateFormatter = nil;
if (!dateFormatter) {
   dateFormatter = [[NSDateFormatter alloc] init];

   NSLocale *enUSPOSIXLocale = [[[NSLocale alloc] 
      initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];
   assert(enUSPOSIXLocale != nil);
   [dateFormatter setLocale:enUSPOSIXLocale];
   [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
   dateFormatter.dateFormat = @"EEE, dd MMM yyyy HH:mm:ss +0000";
}