iOS 13 不使用storyboard 设置rootViewC

遇到不使用storyboard设置rootViewController ，根据很久之前的经验，在appdelegate中的window中设置，结果无效，然后看到了sceneDelegate这个文件，在这个方法中设置

    @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 windowScene = (scene as? UIWindowScene) else { return }
        self.window = UIWindow(windowScene: windowScene)
        let splash = SplashViewController()
        self.window?.rootViewController = splash
        self.window?.makeKeyAndVisible()
    }