谷歌使用firebase登录，检查用户是否已经存在。

Question

我有一个google登录按钮，并存储在firebase.代码如下。

 func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {



        if let error = error {
           // ...
           return
         }

         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 error == nil {
            print("google signed in")

           }
           else
           {
               print(error?.localizedDescription)
           }


         }
    }

它不应该允许用户通过google登录在firebase中，如果这样的用户没有在firebase数据库中创建，如何验证，然后提醒用户这种情况？

Answer 1

我认为要检查一个用户是否存在，你可以使用一个方法来检查。fetchSignInMethods.

func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {



    if let error = error {
       // ...
       return
     }

     guard let authentication = user.authentication else { return }

     guard let email = user.profile.email else { return }

     Auth.auth().fetchSignInMethods(email: email) { (providers, error) in
       if let error = error {
        print(error)
        return
       }

       if let providers = providers { 
        //This returns an array and will tell you if an user exists or not
        //If the user exists you will get providers.count > 0 else 0

         if providers.count > 0 {
          //User Exists and you can print the providers like [google.com, facebook.com] <-- Providers used to sign in
         } else {
          //Show Alert user does not exist
         }
       }


     }

}

Answer 2

因此，你只需要一个条件，即如果用户没有找到，你将呈现一个警报给用户，"用户没有在数据库中创建 "的权利！。

为此，你可以检查GoogleSignIn的错误代码，如:

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 {
                if error._code == AuthErrorCode.userNotFound.rawValue {
                    //Present_your_desired_alert_here
                }
            }

        }