No keyboard showed, when I click on the field. Can anyone spot what is wrong with my code?

class ViewController: UIViewController {

    @IBOutlet weak var nameTextField: UITextField!
    @IBOutlet weak var textFieldBottomConstraint: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()

        NotificationCenter.default.addObserver(self, selector: #selector(ViewController.keyboardWillShow(_:)), name: Notification.Name.UIKeyboardWillShow, object: nil)

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "StartAdventure" {

            do {
                if let name = nameTextField.text {
                    if name == "" {
                        throw AdventureError.nameNotProvided
                    } else {
                        guard let pageController = segue.destination as? PageController else
                            { return }
                        pageController.page = Adventure.story(withName: name)
                    }
                }
            } catch AdventureError.nameNotProvided {
                let alertController = UIAlertController(title: "Name Not Provided", message: "Provide a name to start the story", preferredStyle: .alert)
                let action = UIAlertAction(title: "OK", style: .default, handler: nil)
                alertController.addAction(action)

                present(alertController, animated: true, completion: nil)
            } catch let error {
                fatalError("\(error.localizedDescription)")
            }
        }
    }

    @objc func keyboardWillShow(_ notification: Notification) {
        if let info = notification.userInfo, let keyboardFrame = info [UIKeyboardFrameEndUserInfoKey] as? NSValue {
            let frame = keyboardFrame.cgRectValue
            textFieldBottomConstraint.constant = frame.size.height + 10

            UIView.animate(withDuration: 0.8) {
                self.view.layoutIfNeeded()
            }
        }
    }

    deinit {
    NotificationCenter.default.removeObserver(self)
    }
}

extension ViewController: UITextFieldDelegate {
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        return true
    }
}

```swift