Flutter 如何查看用户之前是否注册过google provider？

Question

我想检查用户之前是否注册过（如果这是他第一次我会让他写一些数据，否则他会进入应用程序的主页）。

GoogleSignInAccount _user;
GoogleSignInAccount get user => _user;

Future googlelogin() async {
  try {
  final googleUser = await googleSignIn.signIn();
  if (googleUser == null) return;
  _user = googleUser;

  final googleAuth = await googleUser.authentication;

  final credential = GoogleAuthProvider.credential(
    accessToken: googleAuth.accessToken,
    idToken: googleAuth.idToken,
  );

  await FirebaseAuth.instance.signInWithCredential(credential);
} catch (e) {
  print(e.toString());
}
notifyListeners();

}

我还有一个 StreamBuilder 来检查用户输入的数据

StreamBuilder<Object>(
      stream: FirebaseAuth.instance.authStateChanges(),
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return Center(
            child: CircularProgressIndicator.adaptive(),
          );
        } else if (snapshot.hasData) {
          return LoggedInWidget();
        } else if (snapshot.hasError) {
          return Center(
            child: Text('Something went wrong'),
          );
        } else {
          return SignUp();
        }
      })

Answer 1

您可以使用“UserCredential”class 的预构建方法“isNewUser”。 从一个变量调用带有凭据 function 的唱歌，并使用该变量执行检查。

...
var result =
        await FirebaseAuth.instance.signInWithCredential(credential);

   if (result.additionalUserInfo!.isNewUser) {

// Perform what you need to do for new users here
// like creating a user document

      }else {

         //Perform what you want to do for old users here
         //like fetching a specific user document

}
...