iPhone上的UIAlertView中的UITextField - 如何使其响应？

import UIKit

let alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)

let textField = UITextField()
alertController.addTextField { (textField) in
    textField.placeholder = "Enter text here"
}

let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
alertController.addAction(cancelAction)

self.present(alertController, animated: true, completion: nil)

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let button = UIButton(frame: CGRect(x: 0, y: 0, width: 100, height: 50))
        button.center = view.center
        button.setTitle("Show Alert", for: .normal)
        button.addTarget(self, action: #selector(showAlert), for: .touchUpInside)
        view.addSubview(button)
    }

    @objc func showAlert() {
        let alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)

        let textField = UITextField()
        alertController.addTextField { (textField) in
            textField.placeholder = "Enter text here"
        }

        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
        alertController.addAction(cancelAction)

        self.present(alertController, animated: true, completion: nil)
    }
}