Objective-C，如何以UTC时区获取当前日期？ [英] Objective-C, How can I get the current date in UTC timezone?

问题描述

我正在尝试：

NSDate *currentDateInLocal = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:SS.SSS'Z'"];
NSString *currentLocalDateAsStr = [dateFormatter stringFromDate:currentDateInLocal];

NSDateFormatter * dateFormatter2 = [[NSDateFormatter alloc] init];
NSTimeZone *timeZone = [NSTimeZone timeZoneWithName:@"UTC"];
[dateFormatter2 setTimeZone:timeZone];
[dateFormatter2 setDateFormat:@"yyyy-MM-dd'T'HH:mm:SS.SSS'Z'"];
NSDate *currentDateInUTC = [dateFormatter2 dateFromString:currentLocalDateAsStr];

但它仍然不代表当前的UTC时间，我该如何实现？

but It's still does not represent the current UTC time, how can I achieve this?

谢谢

推荐答案

NSDate *currentDate = [[NSDate alloc] init];

现在是UTC，（至少在使用下面的方法之后）

要将此时间存储为UTC（自参考日期1970起），请使用

Now it is in UTC, (at least after using the method below)
To store this time as UTC (since refernce date 1970) use

double secsUtc1970 = [[NSDate date]timeIntervalSince1970];

设置日期格式化程序输出当地时间：

Set Date formatter to output local time:

NSTimeZone *timeZone = [NSTimeZone defaultTimeZone];
// or Timezone with specific name like
// [NSTimeZone timeZoneWithName:@"Europe/Riga"] (see link below)
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setTimeZone:timeZone];
[dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"];
NSString *localDateString = [dateFormatter stringFromDate:currentDate];

可用的NSTimeZone名称

A NSDate 对象始终使用UTC作为时间参考，但字符串表示为基于UTC时区，日期不是必需的。

A NSDate object always uses UTC as time reference, but the string representation of a date is not neccessarily based on UTC timezone.

请注意，UTC不是（仅）一个时区，它是一个系统如何测量地球上的时间，它是如何测量的是协调的（UTC中的C代表协调）。

NSDate与UTC时间1.1.1970午夜的参考日期相关，尽管Apple稍微错误地将其描述为1.1.1970 GMT。

Please note that UTC is not (only) a timeZone, It is a system how time on earth is measured, how it is coordinated (The C in UTC stands for coordinated).
The NSDate is related to a reference Date of midnight 1.1.1970 UTC, altough slightly wrongly described by Apple as 1.1.1970 GMT.

在原始问题中，最后一个词timeZone并不完美。

In the original question the last word timeZone is not perfect.

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