Detect whether iPhone is displaying time in 12-Hour or 24-Hour Mode?

Question

How can you detect whether iPhone is displaying time in 12-Hour or 24-Hour Mode?

I currently monitor the current region for changes, however that's not the only setting that affects how times are displayed. The 24-hour toggle in the date & time settings overrides the current regions settings.

Is there any way to detect this 12/14 hour setting?

Consultation

Answer 1

I've figured out a decent way of determining this with a little function I've added to a category of NSLocale. It appears to be pretty accurate and haven't found any problems with it while testing with several regions.

@implementation NSLocale (Misc)
- (BOOL)timeIs24HourFormat {
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateStyle:NSDateFormatterNoStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    NSString *dateString = [formatter stringFromDate:[NSDate date]];
    NSRange amRange = [dateString rangeOfString:[formatter AMSymbol]];
    NSRange pmRange = [dateString rangeOfString:[formatter PMSymbol]];
    BOOL is24Hour = amRange.location == NSNotFound && pmRange.location == NSNotFound;
    [formatter release];
    return is24Hour;
}
@end

Consultation

Answer 2

Are you using the NSDateFormatter class? As far as I know, that respects whatever regional time-format settings the user has in place.

edit - re: your comment:

The format-string comparison might be the right approach. Something along the lines of:

 NSDateComponents *midnightComp = [[NSDateComponents alloc] init];
 [midnightComp setHour:0]
 [midnightComp setMinute:0];
 NSDateFormatter *format = [[NSDateFormatter alloc] init];
 [format setDateStyle:NSDateFormatterNoStyle];
 [format setTimeStyle:NSDateFormatterShortStyle];
 BOOL midnightIsZeros = [[[format stringFromDate:[[NSCalendar currentCalendar] dateFromComponents:midnightComp]] substringToIndex:2] isEqualToString:@"00"];

 [[NSUserDefaults standardUserDefaults] setBool:midnightIsZeros forKey:@"TimeWas24Hour"];

Run that as your app quits, then do it again when the app launches and check it against the value stored in the defaults.

Bunde

I basically need to detect whether that setting has changed since the last load. I can detect the locale identifier, but there's no such setting for the 24 hour setting. Only thing I can think of is to compare a saved formatted date string, but there's issues with timezones and daylight savings which could result issues with direct comparisons. – Consultation

Thanks for that addition, however I've noticed that several regions actually show hours with 0 in 24 hour mode. – Consultation

In that case, grab the first two characters as above, and check whether they're either "00" or "0:". – Bunde

Not all regions use a colon as the hour/minute delimiter ;-) Pretty tricky. But my answer seems to avoid all of this and it working great. Thanks for your help though! – Consultation