override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    NotificationCenter.default.addObserver(forName:Notification.Name(rawValue: kCustomNotification), object:nil, queue:nil) { notification in
        // my code
    }
}

override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    NotificationCenter.default.removeObserver(kCustomNotification)
    NotificationCenter.default.removeObserver(self)
}