Google登录错误:键入'Future<GoogleSignInAccount?>‘不是’GoogleSignInAccount‘类型的子类型？in型铸造

Question

使用FirebaseAuth，我正在尝试将google帐户注册到我的应用程序。

在我的主屏幕上，我单击一个ConnectionPage，导航到LoggedInWidget，它在初始使用时将我转到SignUpWidget，然后单击使用google的登录，它弹出弹出式窗口，允许我选择谷歌用户，此时应该将其路由到LoggedInWidget，但是没有发生任何事情(即快照没有数据)，我一直得到带有错误日志的SignUpWidget ( 721)：输入'Future‘不是’GoogleSignInAccount‘类型在类型转换中的子类型？

在GoogleSignInProvider中有一个转换错误，我无法解决这个错误。有什么帮助吗？

谢谢。

与====相关的属地====

# Google SignIn
  firebase_auth: ^3.2.0
  google_sign_in: ^5.2.1
# Google Icon
  font_awesome_flutter: ^9.2.0

代码片段

==== GoogleSignIn Provider ====

//LIBRARIES

//PACKAGES
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:google_sign_in/google_sign_in.dart';

//PAGES


//utilizing Provider dependency
class GoogleSignInProvider extends ChangeNotifier {
  //class implements the logic of the google sign in when clicking on google sign in button at the SignUpWidget
  final googleSignIn = GoogleSignIn();

  GoogleSignInAccount? _user; // the user that has signed in
  GoogleSignInAccount get user => _user!;

  Future googleLogin() async {
    try {
      final googleUser = googleSignIn
          .signIn(); // user account = account selected in login pop up
      // ignore: unnecessary_null_comparison
      if (googleUser == null) return;
      _user =
          googleUser as GoogleSignInAccount?; // saving account in _user field
      final googleAuth =
          await _user?.authentication; //getting accessToken and IdToken
      final credential = GoogleAuthProvider.credential(
        accessToken: googleAuth!.accessToken,
        idToken: googleAuth.idToken,
      );

      await FirebaseAuth.instance.signInWithCredential(credential); // use credentials to sign into firebaseAuth
    } catch (e) {
      print(e.toString());
    }
    notifyListeners(); // updates the UI
  }

  Future logout() async {
    await googleSignIn.disconnect();
    FirebaseAuth.instance.signOut();
  }
}

====连接页====

//PACKAGES
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';

//PAGES
import '../data/vars.dart';
import '../widget/sign_up_widget.dart';
import '../widget/logged_in_widget.dart';

class ConnectionPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: BG_COLOR,
      body: StreamBuilder(
          stream: FirebaseAuth.instance.authStateChanges(),
          builder: (context, snapshot) {
            // case: connection is waiting
            if (snapshot.connectionState == ConnectionState.waiting) {
              return Center(child: LinearProgressIndicator());
            }
            // case: connection has error
            else if (snapshot.hasError) {
              return Center(
                child: Text(
                  'Something Went Wrong',
                  style: Theme.of(context).textTheme.headline1!.copyWith(),
                ),
              );
            }
            //case: user is logged in already
            else if (snapshot.hasData){
              return LoggedInWidget();
            }
            // case: user is not logged in
            else {
              return SignUpWidget();
                //SignUpWidget();
            }
          }),
    );
  }
}

==== SIGNUPWIDGET ====

//LIBRARIES

//PACKAGES
import 'package:flutter/material.dart';
import 'package:font_awesome_flutter/font_awesome_flutter.dart';
import 'package:provider/provider.dart';

//PAGES
import '../data/vars.dart';
import '../provider/google_sign_in.dart';

class SignUpWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final data = MediaQuery.of(context);
    return Scaffold(
      appBar: AppBar(backgroundColor: BG_COLOR,),
      body: Container(
        color: BG_COLOR,
        height: data.size.height,
        width: data.size.width,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            buildSignUp(context),
          ],
        ),
      ),
    );
  }

    Widget buildSignUp(BuildContext context) =>
        ElevatedButton.icon(
          onPressed: () {
            final provider = Provider.of<GoogleSignInProvider>(context,
                listen: false); // implemented in Provider package
            provider
                .googleLogin(); // user provider to call googleLogin method
          },
          style: Theme
              .of(context)
              .elevatedButtonTheme
              .style!
              .copyWith(),
          label: Text('Google Sign In'),
          icon: FaIcon(FontAwesomeIcons.google, color: Colors.white70,),
        );

}

==== LoggedInWidget ====

//LIBRARIES
//import 'dart:js';

//PACKAGES

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

//PAGES
import '../data/vars.dart';
import '../provider/google_sign_in.dart';

class LoggedInWidget extends StatelessWidget {
  //final FirebaseAuth firebaseAuth = FirebaseAuth.instance;

  @override
  Widget build(BuildContext context) {
    final data = MediaQuery.of(context);
    final user = FirebaseAuth.instance.currentUser!;
    return Scaffold(
      appBar: AppBar(
        title: Text('Logged In'),
        centerTitle: true,
        actions: [
          TextButton(
              onPressed: () {
                final provider = Provider.of<GoogleSignInProvider>(context, listen:false);
                provider.logout();
              },
              child: Text('Log Out')
          )
        ],
      ),
      body: Container(
        height: data.size.height,
        width: data.size.width,
        padding: EdgeInsets.all(16.0),
        decoration: BoxDecoration(
          color: BG_COLOR,
          border: Border.all(
              width: 3.0, color: Colors.grey, style: BorderStyle.solid),
        ),
        alignment: Alignment.center,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              'Profile',
              style: Theme.of(context).textTheme.headline1!.copyWith(),
            ),

            //Display Avatar
            SizedBox(
              height: 20,
            ),
            CircleAvatar(
              radius: 50,
              backgroundImage: NetworkImage(user.photoURL!),
            ),

            //Display Name
            SizedBox(
              height: 8,
            ),
            Text(
              'Name: ' + user.displayName!,
              style: Theme.of(context).textTheme.caption!.copyWith(),
            ),

            //Display Email
            SizedBox(
              height: 8,
            ),
            Text(
              'Email: ' + user.email!,
              style: Theme.of(context).textTheme.caption!.copyWith(),
            ),
          ],
        ),
      ),
    );
  }
}

Answer 1

在这一行中，您丢失了一个await，这就是错误消息的意义所在。改变这一点：

final googleUser = googleSignIn.signIn();

对此：

final googleUser = await googleSignIn.signIn();