在flutter中使用firebase使用google登录时如何检查用户是新用户还是现有用户？

Question

我正在开发一个项目，其中用户数据将保存在Fire存储中，当用户使用谷歌登录时，我正在为用户制作新文档。下面是我的代码

import 'package:firebase_auth/firebase_auth.dart';
import 'package:gfd_official/User/User.dart';
import 'package:gfd_official/services/database.dart';
import 'package:google_sign_in/google_sign_in.dart';

class GSignInhelp {
 final FirebaseAuth _auth = FirebaseAuth.instance;

 //Firebase User
 Userdat _userFromFirebase(User user) {
 return user != null ? Userdat(uid: user.uid) : null;
 }

 //auth change user stream
 Stream<Userdat> get user {
 return _auth.authStateChanges().map(_userFromFirebase);
}

Future signInWithGoogle() async {
GoogleSignIn googleSignIn = GoogleSignIn();
final account = await googleSignIn.signIn();
final auth = await account.authentication;
final credential = GoogleAuthProvider.credential(
accessToken: auth.accessToken,
idToken: auth.idToken,
);
try {
final res = await _auth.signInWithCredential(credential);
User user = res.user;
await DatabaseService(uid: user.uid)
    .updateUserRole(user.displayName, user.email, 'basic');
return _userFromFirebase(user);
} catch (e) {
  print(e.toString());
  return null;
  }
}

Future logOut() async {
try {
  GoogleSignIn().signOut();
  return await _auth.signOut();
} catch (e) {
  print(e.toString());
  return null;
}
}
}

我成功地更改了消防存储中的用户角色，但正如您所看到的，当用户登录时，数据库值将设置为默认值，但我不希望这样。所以，我的问题是如何检查用户是否是首次登录或返回用户。

如果用户返回，那么我不想在 Fire 存储中重置用户数据，如果用户是新用户，则使用默认值在 Fire 存储中创建文档。

结论，当用户使用 google 登录时，我如何检查该用户是现有用户还是新用户？

Answer 1

您可以通过

User Credential

检查用户是否是新用户或之前注册的用户，如果用户尚未注册，您可以通过

authResult.additionalUserInfo.isNewUser

检索。

您可以使用此代码：

 Future<UserCredential> signInWithGoogle(BuildContext context) async {

    FirebaseAuth _auth = FirebaseAuth.instance;
    // Trigger the authentication flow
    final GoogleSignInAccount googleUser = await GoogleSignIn().signIn();

    // Obtain the auth details from the request
    final GoogleSignInAuthentication googleAuth =
        await googleUser.authentication;

    // Create a new credential
    final GoogleAuthCredential credential = GoogleAuthProvider.credential(
      accessToken: googleAuth.accessToken,
      idToken: googleAuth.idToken,
    );

    final UserCredential authResult =
        await _auth.signInWithCredential(credential);

    final User user = authResult.user;

    ///Her to check isNewUser OR Not
    if (authResult.additionalUserInfo.isNewUser) {
      if (user != null) {
      //Ex: Go to RegisterPage()
        }
    } else {
     
      //Ex: Go to HomePage()
    }

    return await FirebaseAuth.instance.signInWithCredential(credential);
  }

Answer 2

这是 Google 登录和退出的完整代码：-

class GSignInhelp {  
final FirebaseAuth _auth = FirebaseAuth.instance;   //Firebase User   
Userdat _userFromFirebaseUser(User user) {    
          return user != null ? Userdat(uid: user.uid) : null;   }   //auth 
         change user stream   
         Stream get user {    
             return _auth.authStateChanges().map(_userFromFirebaseUser);   
        }   
   Future signInWithGoogle() async {     
         GoogleSignIn googleSignIn = 
    GoogleSignIn();