使用标签栏控制器作为根视图控制器，如果用户未登录，则显示登录视图控制器

Question

我已经读过，项目的选项卡栏控制器应该始终是基本控制器，但我想知道，如果用户未登录，如何显示登录视图控制器，然后在用户登录后关闭？

以下是我的代码

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

    let storyboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
    let loginViewController = storyboard.instantiateViewControllerWithIdentifier("signInViewController") as! SignInViewController

    self.window?.makeKeyAndVisible()
    self.window!.rootViewController!.presentViewController(loginViewController, animated: true, completion: nil)

    return true
}

它确实按预期工作，但我在控制台中显示了它。

2016-01-07 12:37:58.139 Fingers[461:67210] Presenting view controllers on detached view controllers is discouraged <AppName.HomeViewController: 0x13ed4f8f0>.
2016-01-07 12:37:58.149 Fingers[461:67210] Unbalanced calls to begin/end appearance transitions for <UITabBarController: 0x13ed4ed60>.

同样这将触发视图在根视图控制器上加载，有什么方法可以避免这种情况？

Answer 1

使用NSNotificationCenter可以很容易地做到这一点。 只需使用提供登录ViewController的方法在TabBarViewController中注册通知即可。

let vc = ViewController() //change this to your class name
self.presentViewController(vc, animated: true, completion: nil)

然后，如果isLogged标志为NO，则可以发布通知以触发上述方法。

登录后，只需将其关闭即可。

self.dismissViewControllerAnimated(true, completion: {});

Answer 2

这是使用App Delegate的didFinishLaunchingWithOptions方法的Firebase的简单示例

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

    var window: UIWindow?
    if Auth.auth().currentUser == nil {
            let storyboard = UIStoryboard(name: "Main", bundle: Bundle.main)
            let authVC = storyboard.instantiateViewController(withIdentifier: "AuthVC")
            window?.makeKeyAndVisible()
            window?.rootViewController?.present(authVC, animated: true, completion: nil)
            return true
    }
    //other things to do at launch if applicable
    return true
}