Datetime format from iPhone settings and GMT offset

问题

I have string with date time format e.g.: 2013-05-28 10:56:31

How can I format this string to the iPhone default format? (in iPhone settings)

And how to set datetime in GMT plus time shift offset (set in iphone too). e.g. GMT+1

Is this possible?

回答1:

You can use NSDateFormatter to achieve this.

NSString *dateString = @"2013-05-28 10:56:31";

NSDateFormatter *formatter = [[NSDateFormatter alloc]init];

//Special Locale for fixed dateStrings
NSLocale *locale = [[NSLocale alloc]initWithLocaleIdentifier:@"en_US_POSIX"];
[formatter setLocale:locale];

//Assuming the dateString is in GMT+00:00
//formatter by default would be set to local timezone 
NSTimeZone *timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0];
[formatter setTimeZone:timeZone];

[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

NSDate *date =[formatter dateFromString:dateString];

//After forming the date set local time zone to formatter    
NSTimeZone *localTimeZone = [NSTimeZone localTimeZone];
[formatter setTimeZone:localTimeZone];

NSString *newTimeZoneDateString = [formatter stringFromDate:date];
NSLog(@"%@",newTimeZoneDateString);

A few pointers for using dateFormatter.

1. If the string don't contain any information about timezone and it is not in same timezone as in the device always set the timezone to the dateFormatter.
2. For fixed format dateStrings always use en_US_POSIX locale
3. NSDate when logged in console always show in GMT+00:00. NSDate don't have timezone, it just differs when represented in different timezone.
4. Convert the formed date to any timezone, by setting new timezone to formatter. Formatter never changes the date it just recalculates how it will be represented in this new timezone.

回答2:

See the documentation about NSDateFormatter, specifically dateFromString, which returns "A date representation of string interpreted using the receiver’s current settings."

来源：https://stackoverflow.com/questions/16790832/datetime-format-from-iphone-settings-and-gmt-offset