Question

I register for being notified in superclass (UIViewController) like so:

SuperClass.m

- (void)viewWillAppear:(BOOL)animated {

    [super viewWillAppear:animated];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(notification:)
                                                 name:@"Notification"
                                               object:nil];
}

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

    // Do something for SuperClass with the notification
}

Now In subclass (subclass of SuperClass.m) I also listen for the same notification like so:

SubClass.m

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

    // Do something specific for SubClass with the notification
}

Is this an acceptable (codewise) way to deal with having a general behaviour when acting on a notification in a superclass and to having a more specific behaviour when acting on a notification in a subclass?

Answer 1

Usually when you want to allow more specific behavior in the subclass, while still maintaining the general behavior in the superclass, you have the subclass call super. For example, the -[UIViewController viewDidAppear:] documentation says:

You can override this method to perform additional tasks associated with presenting the view. If you override this method, you must call super at some point in your implementation.

So your notification setup is fine (although it’s a bit weird to have a NSNotification object as a parameter to a method you expect to be overridden) — but you’ll want to call [super notification:notification] to get the superclass’s behavior as well.