override func viewDidLoad() {
        super.viewDidLoad()

        // 註冊監控
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(keyboardWillShow), // 執行keyboardWillShow function
            name: NSNotification.Name.UIKeyboardWillShow, // 在鍵盤跳出來的時候
            object: nil
        )
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(keyboardWillHide), // 執行keyboardWillHide function
            name: NSNotification.Name.UIKeyboardWillHide, // 在鍵盤收起來的時候
            object: nil
        )
    }

    @objc func keyboardWillShow(_ notification: Notification) {
        // 擷取鍵盤高度，並將view的y座標設定為負的鍵盤高度，這樣view就會往上提高
        if let keyboardFrame: NSValue = notification.userInfo?[UIKeyboardFrameEndUserInfoKey] as? NSValue {
            let keyboardRectangle = keyboardFrame.cgRectValue
            keyboardHeight = keyboardRectangle.height
            self.view.frame = CGRect(x: 0.0, y: -keyboardHeight, width: self.view.frame.width, height: self.view.frame.size.height)
        }
    }
    @objc func keyboardWillHide(_ notification: Notification) {
        // 鍵盤收起來時，就將view歸回原位
        self.view.frame = CGRect(x: 0, y: 0, width: self.view.frame.size.width, height: self.view.frame.size.height)
    }