跳过NavigationController中的登录视图控制器

// 在AppDelegate中设置根视图控制器为NavigationController
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    let rootViewController = UINavigationController(rootViewController: LoginViewController())
    window?.rootViewController = rootViewController
    window?.makeKeyAndVisible()
    return true
}

// 在登录视图控制器中检查用户是否已登录
class LoginViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        if User.isLoggedIn {
            // 用户已登录，推入主视图控制器
            let mainViewController = MainViewController()
            navigationController?.pushViewController(mainViewController, animated: true)
        } else {
            // 用户未登录，替换为登录视图控制器
            let loginViewController = LoginViewController()
            navigationController?.setViewControllers([loginViewController], animated: true)
        }
    }
}

// 主视图控制器
class MainViewController: UIViewController {
    // 主视图控制器的内容
}