从UINavigationItem扩展呈现UIAlertController

extension UINavigationItem {
    func showAlert(title: String?, message: String?, viewController: UIViewController) {
        let alertController = UIAlertController(title: title, message: message, preferredStyle: .alert)
        
        let okAction = UIAlertAction(title: "OK", style: .default, handler: nil)
        alertController.addAction(okAction)
        
        viewController.present(alertController, animated: true, completion: nil)
    }
}

class MyViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 假设你的导航栏项是 self.navigationItem
        self.navigationItem.showAlert(title: "提示", message: "这是一个警告对话框", viewController: self)
    }
}