@objc func promptForAnswer() { let ac = UIAlertController(title: "Enter Answer", message: nil, preferredStyle: .alert)

    ac.addTextField()

    let submitAction = UIAlertAction(title: "Submit", style: .default) {
        [weak self, weak ac] action in
        guard let answer = ac?.textFields?[0].text else {return}
        self?.submit(answer)
    }

    ac.addAction(submitAction)
    present(ac, animated: true)
}

With ac.addTexfield() the alert controller isn't appearing, However, without that line and the closure, the alert is appearing. There's no error, the alert just doesnt appear.

However, in the console I do see Class _PointQueue is implemented in both /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/UIKitCore.framework/UIKitCore (0x10fe0b628) and /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/TextInputUI.framework/TextInputUI (0x12fd836b8). One of the two will be used. Which one is undefined.

Could anyone help please?

Hi there! It is difficult to say with having only part of the code. Basically, I have the same ->

  @objc func promptForAnswer() {
    let ac = UIAlertController(title: "Enter answer", message: nil, preferredStyle: .alert)
    ac.addTextField()

    let submitAction = UIAlertAction(title: "Submit", style: .default) { [weak self, weak ac] _ in
      guard let answer = ac?.textFields?[0].text else { return }
      self?.submit(answer)
    }

    ac.addAction(submitAction)
    present(ac, animated: true)

  }

and this function is called by invoking it from navigation right bar button like that - you should have it in viewDidLoad() ->

navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(promptForAnswer))

Thank you @ygeras , I have the same code as yours, even the invoking of the rightBarButton in the viewDidLoad(). I'm not sure, why it doesn't appear with textfield method ac.addTextField() . The alert appears If I just comment that and the closure of the UIAlertAction.

Try to Clean Build Folder by pressing Shift+Cmd+K. As an option try to add print("TextField added") or other print statements in the flow to check where the issue is...

 let ac = UIAlertController(title: "Enter answer", message: nil, preferredStyle: .alert)
    ac.addTextField()

    print("TextField added")