如何从 App Delegate 切换到不同的视图控制器？

Question

用户使用 Google 登录后，我想将他们带到主屏幕；但是，代码并没有完全执行。

这是代码：

func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!,
              withError error: Error!) {
      if let error = error {
        if (error as NSError).code == GIDSignInErrorCode.hasNoAuthInKeychain.rawValue {
          print("The user has not signed in before or they have since signed out.")
        } else {
          print("\(error.localizedDescription)")
        }
        return
      }
        let firstName = user.profile.givenName
        let lastName = user.profile.familyName
        let email = user.profile.email
    //Firebase sign in
      guard let authentication = user.authentication else {return}
        let credential = GoogleAuthProvider.credential(withIDToken: authentication.idToken, accessToken: authentication.accessToken)

        Auth.auth().signIn(with: credential) { (authResult, error) in
            if let error = error {
                print("Firebase sign In error")
                print(error)
                return
            } else {
                let db = Firestore.firestore()

                db.collection("users").addDocument(data: ["firstName": firstName!, "lastName": lastName!, "email": email!, "uid": authResult!.user.uid]) { (error) in

                    if error != nil {
                        print("Error: User data not saved")
                    }
            }
            print("User is signed in with Firebase")
            let mainStoryboard:UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
            let homeViewController = mainStoryboard.instantiateViewController(withIdentifier: "HomeVC") as! HomeViewController
            self.window?.rootViewController = homeViewController
            self.window?.makeKeyAndVisible()

        }
    }
}

更具体地说：

Auth.auth().signIn(with: credential) { (authResult, error) in
            if let error = error {
                print("Firebase sign In error")
                print(error)
                return
            } else {
                let db = Firestore.firestore()

                db.collection("users").addDocument(data: ["firstName": firstName!, "lastName": lastName!, "email": email!, "uid": authResult!.user.uid]) { (error) in

                    if error != nil {
                        print("Error: User data not saved")
                    }
            }
            print("User is signed in with Firebase")
            let mainStoryboard:UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
            let homeViewController = mainStoryboard.instantiateViewController(withIdentifier: "HomeVC") as! HomeViewController
            self.window?.rootViewController = homeViewController
            self.window?.makeKeyAndVisible()

        }
    }

print("User is signed in with Firebase") 确实发生了，但它无法切换 HomeViewController，我不确定我在这里做错了什么。

Answer 1

我的猜测是 window 为 nil，这就是您的代码无法正常执行的原因。如果您的目标是 iOS 13，请尝试以下代码。理想情况下，如果您的应用还支持 iOS 12、11 等，您可能希望将登录代码移动到 SceneDelegate 中并在 AppDelegate 中复制它。

   Auth.auth().signIn(with: credential) { (authResult, error) in
        if let error = error {
            print("Firebase sign In error")
            print(error)
            return
        } else {
            let db = Firestore.firestore()

            db.collection("users").addDocument(data: ["firstName": firstName!, "lastName": lastName!, "email": email!, "uid": authResult!.user.uid]) { (error) in

                if error != nil {
                    print("Error: User data not saved")
                }
            }
            print("User is signed in with Firebase")
            DispatchQueue.main.async {
                let scene = UIApplication.shared.connectedScenes.first
                if let sceneDelegate = scene?.delegate as? SceneDelegate {  
                    let window = sceneDelegate?.window
                    let mainStoryboard:UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
                    let homeViewController = mainStoryboard.instantiateViewController(withIdentifier: "HomeVC") as! HomeViewController
                    window?.rootViewController = homeViewController
                    window?.makeKeyAndVisible()

                }
            }
        }
    }

Answer 2

代码中的问题是 Firebase 是异步的。所以本节

} else {
   let db = Firestore.firestore()

   db.collection("users").addDocument(data: ["firstName": firstName!, "lastName": lastName!, "email": email!, "uid": authResult!.user.uid]) { (error) in

      if error != nil {
         print("Error: User data not saved")
      }
   }

   print("User is signed in with Firebase")

这个打印语句

print("User is signed in with Firebase")

将在闭包内的代码之前执行。原因是代码比互联网快 - 您必须“等待”数据从 Firebase 返回，然后才能继续执行代码。要解决此问题，请移动闭包内的语句，以便它们在 Firebase 返回时执行

} else {
   let db = Firestore.firestore()

   db.collection("users").addDocument(data: ["firstName": firstName!, "lastName": lastName!, "email": email!, "uid": authResult!.user.uid]) { (error) in

      if error != nil {
         print("Error: User data not saved")
         return
      }

      print("User is signed in with Firebase")
      let mainStoryboard:UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
      let homeViewController = mainStoryboard.instantiateViewController(withIdentifier: "HomeVC") as! HomeViewController
      self.window?.rootViewController = homeViewController
      self.window?.makeKeyAndVisible()
    }

请注意，使用此代码流，每次现有用户签名时，都会在 users 集合中创建一个新文档。这可能不是本意。