ios - 在 swift 中以编程方式创建 navigationController 时，ViewController 出现多次

Question

我一直在以编程方式完全从头开始创建我的应用程序，没有使用 Storyboard 。

我的应用程序与 Firebase 集成，并使用 Facebook 登录。

我的设置相当简单:

1. Launch the app -> takes you to the first VC called WelcomeViewController.
2. There is a check that happens in the viewDidLoad method to see if a user is already signed in and exists. If there is, it sends you straight to the second VC called FilmsViewController
3. The FilmsViewController is a collectionViewController that displays films. The user can press a film, and it takes them to more information about that film.

(作为引用，我已经在我的应用程序中登录了 Facebook)

我有一个当前问题，当上面的第 2 步发生时，它会转换到 FilmsViewController，但它会转换 2 或 3 次。所以你看到新的 VC 出现了 2 或 3 次，然后内容加载了。如果您按下导航栏中的 Back 按钮，它会带您返回到它加载的 2 或 3 个 viewController，然后再返回到 WelcomeViewController。

我的观点如下。

在 AppDelegate.swift 中:

var window: UIWindow?
var navController: UINavigationController?

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.

    navController = UINavigationController()
    let firstViewController: WelcomeViewController = WelcomeViewController()
    self.navController!.pushViewController(firstViewController, animated: true)

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

    return true

}

在 viewDidLoad 的 WelcomeViewController 中:

FIRAuth.auth()?.addStateDidChangeListener { auth, user in

        if let user = user {

            // User is signed in.
            // Direct the user to the home screen

            let toFilmListVC = FilmsViewController(collectionViewLayout: UICollectionViewFlowLayout())
            self.navigationController?.pushViewController(toFilmListVC, animated: true)

        } else { ...
        }
}

我找了很多解决方案 - 但一无所获。我只找到一篇关于这个问题的帖子，有人说解决方案是更改该 Controller 的类名，我已经这样做了，但没有任何改变。

谁能帮我解决这个问题？谢谢。

Answer 1

addStateDidChangeListener 可能被调用了多次。

你应该修改它来检查一个 FilmsViewController 是否已经被推送，以防止推送另一个:

FIRAuth.auth()?.addStateDidChangeListener { auth, user in

    if let user = user {

        // User is signed in.
        // Direct the user to the home screen

        // Only push one FilmsViewController onto the navigation stack!
        var shouldPush = true
        if let navigationController = self.navigationController {
            for viewController in navigationController.viewControllers {
                if viewController is FilmsViewController {
                    shouldPush = false
                }
            }
        }

        if shouldPush {
            let toFilmListVC = FilmsViewController(collectionViewLayout: UICollectionViewFlowLayout())
            self.navigationController?.pushViewController(toFilmListVC, animated: true)
        }
    } else { ...
    }
}