NavigationBar未出现

Question

我试着做一个有两个视图控制器的应用程序。第一个是LoginViewController，第二个是MainViewController，MainViewController有一个导航栏。我在SceneDelegate中设置了初始视图控制器，如下所示：

guard let windowScene = (scene as? UIWindowScene) else { return }
        window = UIWindow(frame: UIScreen.main.bounds)
        window?.windowScene = windowScene
        
 // a user is currently logged in

        if let _ = Auth.auth().currentUser {
          UIViewController.showViewController(storyBoardName: "Main", viewControllerId: "MainViewController")
        } else { 
            
 // no logged in user

          UIViewController.showViewController(storyBoardName: "Main", viewControllerId: "LoginViewController")
        }

        window?.makeKeyAndVisible()
      }
    }

这很好用，但是导航栏没有出现，我搜索了一下，发现初始的视图控制器应该是导航控制器，而不是MainViewController，所以我这样做：

guard let windowScene = (scene as? UIWindowScene) else { return }
        window = UIWindow(frame: UIScreen.main.bounds)
        window?.windowScene = windowScene
        
 // a user is currently logged in

        if let _ = Auth.auth().currentUser {
          UIViewController.showViewController(storyBoardName: "Main", viewControllerId: "MainViewController")
        } else { 
            
 // no logged in user

  let vc = MainViewController()
            let nav = UINavigationController(rootViewController: vc)
            nav.navigationBar.barTintColor = .white
            nav.navigationBar.isTranslucent = false
            nav.navigationBar.tintColor = .black
            self.window = UIWindow(frame: UIScreen.main.bounds)
            self.window!.rootViewController = nav
            self.window?.makeKeyAndVisible()
}
    }

但是，导航栏仍然没有显示

Answer 1

在用户登录后，您必须以根用户身份创建MainViewController

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
    // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
    // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).
    
    guard let _ = (scene as? UIWindowScene) else { return }
    
    // a user is currently logged in
    
    if isUserLoggedIn {
        
        let vc = LoginViewController()
        let nav = UINavigationController(rootViewController: vc)
        nav.navigationBar.barTintColor = .white
        nav.navigationBar.isTranslucent = false
        nav.navigationBar.tintColor = .black
        self.window = UIWindow(frame: UIScreen.main.bounds)
        self.window!.rootViewController = nav
        self.window?.makeKeyAndVisible()
        
    } else {
        let vc = ViewController()
        let nav = UINavigationController(rootViewController: vc)
        nav.navigationBar.barTintColor = .white
        nav.navigationBar.isTranslucent = false
        nav.navigationBar.tintColor = .black
        self.window = UIWindow(frame: UIScreen.main.bounds)
        self.window!.rootViewController = nav
        self.window?.makeKeyAndVisible()
        
    }
}