medium-form-combine-vc-part3.swift

func setupPublishers() {
    // 1
    NotificationCenter.default
        .publisher(for: UITextField.textDidChangeNotification, object: emailTextField)
        .map { ($0.object as! UITextField).text ?? "" }
        .assign(to: \.email, on: viewModel)
        .store(in: &cancellables)

    NotificationCenter.default
        .publisher(for: UITextField.textDidChangeNotification, object: passwordTextField)
        .map { ($0.object as! UITextField).text ?? "" }
        .assign(to: \.password, on: viewModel)
        .store(in: &cancellables)
    
    // 2
    viewModel.isSubmitEnabled
        .assign(to: \.isEnabled, on: submitButton)
        .store(in: &cancellables)

    // 3
    viewModel.$state
        .sink { [weak self] state in
            switch state {
            case .loading:
                self?.submitButton.isEnabled = false
                self?.submitButton.setTitle("Loading..", for: .normal)
                self?.hideError(true)
            case .success:
                self?.showResultScreen()
                self?.resetButton()
                self?.hideError(true)
            case .failed:
                self?.resetButton()
                self?.hideError(false)
            case .none:
                break
            }
        }
        .store(in: &cancellables)
}

@objc func onSubmit() {
    // 4
    viewModel.submitLogin()
}

func resetButton() {
    // 5
    submitButton.setTitle("Login", for: .normal)
    submitButton.isEnabled = true
}

func showResultScreen() {
    // show another view controller once success
}

// 6
func hideError(_ isHidden: Bool) {
    errorLabel.alpha = isHidden ? 0 : 1
}