swift - 第一次启动应用程序 xcode 时出现黑屏

Question

我在第一次使用空白屏幕登录应用程序时遇到了一个小问题，并且收到警告“尝试呈现不在窗口层次结构中的 View !”关闭并重新启动后， View 看起来不错。我相信它与 rootViewController 有关，但不确定......提前感谢您的任何帮助或指导!

应用程序委托(delegate)

    @UIApplicationMain
    class AppDelegate: UIResponder, UIApplicationDelegate {

        var window: UIWindow?
        var ref:FIRDatabaseReference?
        var databaseHandle:FIRDatabaseHandle?

        func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

            window = UIWindow(frame: UIScreen.main.bounds)
            window?.makeKeyAndVisible()
            window?.rootViewController = MainNavigationController()

            FIRApp.configure()
            ref = FIRDatabase.database().reference()

            return true
        }

导航 Controller 为 rootViewController

    class MainNavigationController: UINavigationController {

        var segmentedController: UISegmentedControl!

        override func viewDidLoad() {
            super.viewDidLoad()

            let vc1 = TravelersFeedVC()
            let vc2 = ProfileVC()

            if isLoggedIn() {
                // assume user is logged in
                let homeController = HomeController()
                viewControllers = [homeController]
                homeController.firstViewController = vc1
                homeController.secondViewController = vc2


            } else {
                perform(#selector(showLoginController), with: nil, afterDelay: 0.01)
            }
        }

        fileprivate func isLoggedIn() ->  Bool {
            return UserDefaults.standard.isLoggedIn()
        }

        func showLoginController() {
            let loginController = LoginController()
            present(loginController, animated: true, completion: {
                // perhaps do something here later
            })
        }
    }

//登录函数调用

    func finishLoggingIn() {
        let rootViewController = UIApplication.shared.keyWindow?.rootViewController
        guard let mainNavigationController = rootViewController as? MainNavigationController else { return }

        let vc1 = TravelersFeedVC()
        let vc2 = ProfileVC()

        if isLoggedIn() {
            // assume user is logged in
            let homeController = HomeController()
            mainNavigationController.viewControllers = [HomeController()]
            homeController.firstViewController = vc1
            homeController.secondViewController = vc2

        } else {
            perform(#selector(showLoginController), with: nil, afterDelay: 0.01)
        }
        UserDefaults.standard.setIsLoggedIn(value: true)
        dismiss(animated: true, completion: nil)
    }

Answer 1

好吧，所以我的最后一个答案是错误的(我删除了它)，问题是应用程序中有一个键窗口，这是你的导航 Controller ，并且你不能在这个窗口上呈现任何内容，直到它加载其 subview (即使它没有任何)，这会发生在 viewdidappear 上，因此您应该将 viewdidload 中的代码放在那里。