NSNotification

## UIApplicationSignificantTimeChangeNotification : 날짜 시간이 변경될때 알림

NSNotificationCenter *noteCenter = [NSNotificationCenter defaultCenter];
[noteCenter addObserver:self
               selector:@selector(notiSignificantTimeChanged:)
                   name:UIApplicationSignificantTimeChangeNotification
                 object:nil];

- (void)notiSignificantTimeChanged:(NSNotification *)notification {
}