Detect iPhone 24-Hour time setting

Question

I'm using a UIDatePicker to select a time. I am also customising the background of the picker, however I need 2 different images depending on whether the user is using 12 hour mode (which displays AM/PM column) or 24 hour mode. How can I detect the users setting for the 12/24 hour time?

Thanks

Answer 1

Even shorter than the others:

NSString *format = [NSDateFormatter dateFormatFromTemplate:@"j" options:0 locale:[NSLocale currentLocale]];
BOOL is24Hour = ([format rangeOfString:@"a"].location == NSNotFound);

Explanation

The string formatting character to represent the am/pm symbol is "a", as documented in Unicode Locale Markup Language – Part 4: Dates.

The same document also explains the special template symbol "j":

This is a special-purpose symbol. It must not occur in pattern or skeleton data. Instead, it is reserved for use in skeletons passed to APIs doing flexible date pattern generation. In such a context, it requests the preferred hour format for the locale (h, H, K, or k), as determined by whether h, H, K, or k is used in the standard short time format for the locale. In the implementation of such an API, 'j' must be replaced by h, H, K, or k before beginning a match against availableFormats 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).

The NSString method dateFormatFromTemplate:options:locale: is described in Apple's NSDateFormatter documentation:

Returns a localized date format string representing the given date format components arranged appropriately for the specified locale.

So, what that method will do is turn the @"j" you pass in as a template in to a format string suitable for NSDateFormatter. If this string contains the am / pm symbol @"a" in it anywhere, then you know the locale (and other user settings being interrogated by the OS for you) wants am / pm to be displayed.