类型'NSNotification.Name'没有成员'UIResponder'...这是我得到的错误

Question

我在我的项目中使用firebase并出现以下错误：

  

类型“ NSNotification.Name”没有成员“ UIResponder”

这是我的代码：

override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        emailField.becomeFirstResponder()
        NotificationCenter.default.addObserver(self, selector:#selector(keyboardWillAppear), name: NSNotification.Name.UIResponder.keyboardWillShowNotification, object: nil)

}