gistfile1.txt

BOOL isBackgroundingAvailable = (&UIApplicationDidEnterBackgroundNotification != NULL);
if (isBackgroundingAvailable) {
  [[NSNotificationCenter defaultCenter] addObserver:self
                                           selector:@selector(applicationWillEnterForegroundNotification:)
                                               name:UIApplicationWillEnterForegroundNotification
                                             object:nil];
}