iOS -移动到后台时密码保存警报控制器消失-如何保留UIAlertController？

import UIKit

class ViewController: UIViewController {
    var alertController: UIAlertController?

    override func viewDidLoad() {
        super.viewDidLoad()
        // 初始化UIAlertController
        alertController = UIAlertController(title: "提示", message: "密码保存成功！", preferredStyle: .alert)
        let okAction = UIAlertAction(title: "确定", style: .default, handler: nil)
        alertController?.addAction(okAction)
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        // 显示UIAlertController
        if let alertController = alertController {
            present(alertController, animated: true, completion: nil)
        }
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        // 应用程序即将进入后台，保存UIAlertController的引用
        NotificationCenter.default.addObserver(self, selector: #selector(saveAlertController), name: UIApplication.willResignActiveNotification, object: nil)
    }

    @objc func saveAlertController() {
        // 保存UIAlertController的引用
        if let alertController = alertController {
            // 将UIAlertController保存到合适的数据结构中，或者声明为全局变量
            // 例如：SavedAlertController.shared.alertController = alertController
        }
    }
}