NSDateFormatter in 12-hour mode

问题

I have the following code.

NSDateFormatter *df = ...;
[df setTimeZone:[NSTimeZone defaultTimeZone]];
[df setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSSZZZ"];
NSDate * date = [df dateFromString:date_string]; //here is the problem

In 24-hour mode everything is ok. When 12-hour mode is set on device, stringFromDate returns null. Format of date_string is the same all the time, date format too. Why does it happen?

回答1:

Try to set the locale in this way :

NSLocale *twelveHourLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
df.locale = twelveHourLocale;

To force instead to 24 hour, you can use :

NSLocale *twentyFour = [[NSLocale alloc] initWithLocaleIdentifier:@"en_GB"];

回答2:

In your NSDateFormatter "yyyy-MM-dd'T'HH:mm:ss.SSSZZZ" HH stands for 24 hour and hh stands for 12 hour

回答3:

12-hour mode to 24 hour mode:

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"hh:mm a"];
NSDate *amPmDate = [formatter dateFromString:amPmHourString];
[formatter setDateFormat:@"HH:mm"];
NSString *24HourString = [formatter stringFromDate:amPmDate]];

For 24-hour mode to 12 hour mode just do the opposite

回答4:

NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
NSLocale *locale = [[[NSLocale alloc] 
                initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];  
[dateFormat setLocale:locale];

来源：https://stackoverflow.com/questions/11062280/nsdateformatter-in-12-hour-mode