无法在 AppDelegate 中以编程方式将 viewContoller 添加到选项卡栏

Question

我正在尝试通过 didFinishLaunchWithOptions 以编程方式将 viewController 添加到现有选项卡栏，但我的代码不起作用，我无法将 rootViewController 向下转换为 UITabBarController。

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
        if let tabBarController = window?.rootViewController as? UITabBarController {
            print("rootVC")
            let storyboard = UIStoryboard(name: "Main", bundle: nil)
            let vc = storyboard.instantiateViewController(withIdentifier: "NavController")
            vc.tabBarItem = UITabBarItem(tabBarSystemItem: .topRated, tag: 1)
            tabBarController.viewControllers?.append(vc)
        }

        return true
    }

这是我的故事板，我觉得这里没问题，Tab Bar Contoller 是初始视图控制器...

Main.storyboard

Answer 1

在 iOS 13+ 中，应用程序委托中的 didFinishLaunchingWithOptions 中的 window 将为零。而是将代码移动到 SceneDelegate:

中的 willConnectTo session 方法

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    if let tabBarController = window?.rootViewController as? UITabBarController {
        print("rootVC")
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let vc = storyboard.instantiateViewController(withIdentifier: "NavController")
        vc.tabBarItem = UITabBarItem(tabBarSystemItem: .topRated, tag: 1)
        tabBarController.viewControllers?.append(vc)
    }
    guard let _ = (scene as? UIWindowScene) else { return }
}

无法在 AppDelegate 中以编程方式将 viewContoller 添加到选项卡栏

Can't add viewContoller to Tab Bar programmatically in the AppDelegate

ios

swift

xcode

downcast