How to detect the system time format change in ios?

Question

I want to detect the time format change done in the system setting. I used following code but it always give me the time old format. How can i get new time format?

#pragma mark
#pragma mark - application change time format
-(void)applicationSignificantTimeChange:(UIApplication *)application
{
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setLocale:[NSLocale currentLocale]];
    [formatter setDateStyle:NSDateFormatterNoStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    [formatter setTimeZone:[NSTimeZone localTimeZone]];
    NSString *dateString = [formatter stringFromDate:[NSDate date]];
    NSLog(@"dataString ::%@",dateString);
    NSRange amRange = [dateString rangeOfString:[formatter AMSymbol]];
    NSRange pmRange = [dateString rangeOfString:[formatter PMSymbol]];
    is12Hour = (amRange.length > 0 || pmRange.length > 0);
}

Answer 1

I'm not sure why you expect that the dateFormat changes if the date changes significantly.
The significant time change event is triggered when the time (i.e. [NSDate date]) changes. For example if a new day starts, if the user changes timezone or if daylight-saving starts or ends.
But those events don't change the date format.

I think you want to monitor locale changes. There is a notification for that: NSCurrentLocaleDidChangeNotification.

Something like this should work:

j is a template that will be replaced with h a (12 hour format) or H (24 hour format) by the date template method

id localeDidChangeNotification = [[NSNotificationCenter defaultCenter] addObserverForName:NSCurrentLocaleDidChangeNotification object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *note) {
    NSString *dateFormat = [NSDateFormatter dateFormatFromTemplate:@"j" options:0 locale:[NSLocale currentLocale]];
    if ([dateFormat rangeOfString:@"h"].location != NSNotFound) {
        // 12 hour
    }
    else {
        // 24 hour
    }
}];

// Don't forget to remove the notification in the appropriate place
// [[NSNotificationCenter defaultCenter] removeObserver:localeDidChangeNotification];

Answer 2

Store time format of system. store it in NSUserDefaults say PtimeFormat Next time on application launched check if PtimeFormat exists. get once again time format of system and match both format, whether they are same or not.