Only the UIApplicationDelegate
defines those methods. If you want any other class to handle those events, you need to have the class register for the corresponding notification.
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(backgrounding) name:UIApplicationDidEnterBackgroundNotification object:nil];
And don't forget to remove the observer.
Then you need the method:
- (void)backgrounding {
// App entered background
}