UIAlertController的文本字段Swift出现问题

let alertController = UIAlertController(title: "标题", message: "消息", preferredStyle: .alert)

// 添加文本字段
alertController.addTextField { textField in
    textField.placeholder = "请输入文本"
}

// 添加取消按钮
let cancelAction = UIAlertAction(title: "取消", style: .cancel, handler: nil)
alertController.addAction(cancelAction)

// 添加确定按钮
let okAction = UIAlertAction(title: "确定", style: .default) { action in
    if let textField = alertController.textFields?.first {
        let text = textField.text ?? ""
        // 处理用户输入的文本
        print("用户输入的文本：\(text)")
    }
}
alertController.addAction(okAction)

// 显示UIAlertController
present(alertController, animated: true, completion: nil)