NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; [formatter setLocale:[NSLocale currentLocale]]; [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 is24h = (amRange.location == NSNotFound && pmRange.location == NSNotFound);
NSString *formatStringForHours = [NSDateFormatter dateFormatFromTemplate:@"j" options:0 locale:[NSLocale currentLocale]]; NSRange containsA = [formatStringForHours rangeOfString:@"a"]; BOOL is24h = containsA.location == NSNotFound;
This uses a special date template string called "j" which according to the ICU Spec ...
[...] requests the preferred hour format for the locale (h, H, K, or k), as determined by the preferred attribute of the hours element in supplemental data. [...] Note that use of 'j' in a skeleton passed to an API is the only way to have a skeleton request a locale's preferred time cycle type (12-hour or 24-hour).
That last sentence is important. It "is the only way to have a skeleton request a locale's preferred time cycle type". Since
NSCalendar are built on the ICU library, the same holds true here.
The second option was derived from this answer.