title: Type 'NSNotification.Name' has no member 'UITextField'
body: <p>With Swift 4.2, getting following error, that was working fine with Swift 4.</p>
  
  <blockquote>
    <p>Type 'NSNotification.Name' has no member 'UITextField'</p>
  </blockquote>
  
  <p>Here is my error code.</p>
  
  <pre><code>NotificationCenter.default.addObserver(forName: NSNotification.Name.UITextField.textDidChangeNotification, object: textField, queue: OperationQueue.main) { (notification) in
              loginAction.isEnabled = textField.text != ""
          }
  </code></pre>
  
  <p>Full Code:</p>
  
  <pre><code>@IBAction func alertWithLogin(){
  
      let alertController = UIAlertController(title: "Please Enter Credential", message: nil, preferredStyle: .alert)
  
      // ADD ACTIONS HANDLER
      let loginAction = UIAlertAction(title: "Login", style: .default) { (_) in
  
          let loginTextField = alertController.textFields![0] as UITextField
          let passwordTextField = alertController.textFields![1] as UITextField
  
          // do something with after login
      }
      loginAction.isEnabled = false
      alertController.addAction(loginAction)
  
      let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) { (_) in
          // do something
      }
      alertController.addAction(cancelAction)
  
      // ADD TEXT FIELDS
      alertController.addTextField { (textField) in
          textField.placeholder = "Email"
      }
      alertController.addTextField { (textField) in
          textField.placeholder = "Password"
          textField.isSecureTextEntry = true
  
          // enable login button when password is entered
          NotificationCenter.default.addObserver(forName: NSNotification.Name.UITextField.textDidChangeNotification, object: textField, queue: OperationQueue.main) { (notification) in
              loginAction.isEnabled = textField.text != ""
          }
      }
  
      // PRESENT
      present(alertController, animated: true)
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/4oPMD.png" rel="noreferrer"><img src="https://i.stack.imgur.com/4oPMD.png" alt="enter image description here"></a></p>