xcode: Version 11.3.1 (11C504)
iOS: 13
语言：Swift/Objective-C

资料参考链接

指定根视图,兼容iOS13以及iOS13之前的系统：

SceneDelegate.swift文件中修改

@available(iOS 13.0, *)
    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 winScene = (scene as? UIWindowScene) else { return }

        // Create the root view controller as needed
        let vc = LoginViewController()
        let nc = UINavigationController(rootViewController: vc)

        // Create the window. Be sure to use this initializer and not the frame one.
        let win = UIWindow(windowScene: winScene)
        win.rootViewController = nc
        win.makeKeyAndVisible()
        window = win
    }

AppDelegate.swift文件中修改

var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        window = UIWindow(frame: UIScreen.main.bounds)
        
        let loginVC = LoginViewController()
        let navi = UINavigationController(rootViewController: loginVC)
        window?.rootViewController = navi
        window?.makeKeyAndVisible()
        
        return true
    }

2021年2月5号更新：
更新内容Objective-C版本。
Appdelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    CGRect mainRect = [UIScreen mainScreen].bounds;
    self.window = [[UIWindow alloc]initWithFrame:mainRect];
    
    MainViewController *mainVC = [[MainViewController alloc]init];
    UINavigationController *naviVC = [[UINavigationController alloc]initWithRootViewController:mainVC];
    
    self.window.rootViewController = naviVC;
    [self.window makeKeyAndVisible];
    
    return YES;
}

SceneDelegate

- (void)scene:(UIScene *)scene willConnectToSession:(UISceneSession *)session options:(UISceneConnectionOptions *)connectionOptions  API_AVAILABLE(ios(13.0)){
    // 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).
    
    
    UIWindowScene *windowScene = [[UIWindowScene alloc]initWithSession:session connectionOptions:connectionOptions];
    self.window = [[UIWindow alloc]initWithWindowScene:windowScene];
    
    MainViewController *mainVC = [[MainViewController alloc]init];
    UINavigationController *naviVC = [[UINavigationController alloc]initWithRootViewController:mainVC];
    
    self.window.rootViewController = naviVC;
    [self.window makeKeyAndVisible];
}

完美结束