Sad View Controller example for https://medium.com/@PatrykPeszko/notification-pattern-a862ceff4226

HappyPaymentViewController.swift

// It's just an example for notifications. The rest can be safely ignored :)
class HappyPaymentViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        PaymentNotifications.accepted.observe(self,
            selector: #selector(HappyPaymentViewController.paymentNotificationReceived(_:)))
        PaymentNotifications.rejected.observe(self,
            selector: #selector(HappyPaymentViewController.paymentNotificationReceived(_:)))
    }

    func paymentServiceDidReturn(paymentResponse: PaymentResponse) {
        switch paymentResponse {
        case .Accepted(_):
            PaymentNotifications.accepted.post()
        case .Rejected(_):
            PaymentNotifications.rejected.post()
        }
    }

    func paymentNotificationReceived(notification: NSNotification) {
        //FIXIT: Write this code before release, okay? Bye, I'm off for vacation. ᕕ( ᐛ )ᕗ
    }

    deinit {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }
    
}