flutter - 未处理的异常：NoSuchMethodError：在 null 上调用了方法“[]”。尝试调用：[]("username")

Question

Bonjour tout le monde,

我的控制台中有此错误消息，我搜索了几天没有找到答案。

错误消息：未处理的异常：NoSuchMethodError：在 null 上调用了方法“[]”。尝试调用：

你能帮助我吗？这是我的代码：

final auth = FirebaseAuth.instance;
final googleSignIn = GoogleSignIn();
final ref = FirebaseFirestore.instance.collection('Users');
final FirebaseMessaging _firebaseMessaging = FirebaseMessaging();


Users currentUserModel;

Future<void> main() async {

  WidgetsFlutterBinding.ensureInitialized(); // after upgrading flutter this is now necessary
  await Firebase.initializeApp();
  // enable timestamps in firebase
  runApp(MyApp());
}

Future<Null> _ensureLoggedIn(BuildContext context) async {
  GoogleSignInAccount user = googleSignIn.currentUser;
  if (user == null) {
    user = await googleSignIn.signInSilently();
  }
  if (user == null) {
    await googleSignIn.signIn();
    await tryCreateUserRecord(context);
  }

  if (await auth.currentUser == null) {

    final GoogleSignInAccount googleUser = await googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth = await googleUser
        .authentication;


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

    await auth.signInWithCredential(credential);
  }
}

Future<Null> _silentLogin(BuildContext context) async {
  GoogleSignInAccount user = googleSignIn.currentUser;

  if (user == null) {
    user = await googleSignIn.signInSilently();
    await tryCreateUserRecord(context);
  }

  if (await auth.currentUser == null && user != null) {
    final GoogleSignInAccount googleUser = await googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth = await googleUser
        .authentication;


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

    await auth.signInWithCredential(credential);
  }


}

Future<Null> _setUpNotifications() async {
  if (Platform.isAndroid) {
    _firebaseMessaging.configure(
      onMessage: (Map<String, dynamic> message) async {
        print('on message $message');
      },
      onResume: (Map<String, dynamic> message) async {
        print('on resume $message');
      },
      onLaunch: (Map<String, dynamic> message) async {
        print('on launch $message');
      },
    );

    _firebaseMessaging.getToken().then((token) {
      print("Firebase Messaging Token: " + token);

      FirebaseFirestore.instance
          .collection("Users")
          .doc(currentUserModel.id)
          .update({"androidNotificationToken": token});
    });
  }
}

Future<void> tryCreateUserRecord(BuildContext context) async {
  GoogleSignInAccount user = googleSignIn.currentUser;
  if (user == null) {
    return null;
  }
  DocumentSnapshot userRecord = await ref.doc(user.id).get();
  if (userRecord.data == null) {
    // no user record exists, time to create

    String userName = await Navigator.push(
      context,
      MaterialPageRoute(
          builder: (context) => Center(
                child: Scaffold(
                    appBar: AppBar(
                      leading: Container(),
                      title: Text('Fill out missing data',
                          style: TextStyle(
                              color: Colors.black,
                              fontWeight: FontWeight.bold)),
                      backgroundColor: Colors.white,
                    ),
                    body: ListView(
                      children: <Widget>[
                        Container(
                          child: CreateAccount(),
                        ),
                      ],
                    )),
              )),
    );

    if (userName != null || userName.length != 0) {
      ref.doc(user.id).set({
        "id": user.id,
        "username": userName,
        "photoUrl": user.photoUrl,
        "email": user.email,
        "displayName": user.displayName,
        "bio": "",
        "followers": {},
        "following": {},
      });
    }
    userRecord = await ref.doc(user.id).get();
  }

  currentUserModel = Users.fromDocument(userRecord);
  return null;
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'MyApp',
      theme: ThemeData(
          // This is the theme of your application.
          //
          // Try running your application with "flutter run". You'll see the
          // application has a blue toolbar. Then, without quitting the app, try
          // changing the primarySwatch below to Colors.green and then invoke
          // "hot reload" (press "r" in the console where you ran "flutter run",
          // or press Run > Flutter Hot Reload in IntelliJ). Notice that the
          // counter didn't reset back to zero; the application is not restarted.
          primarySwatch: Colors.blue,
          buttonColor: Colors.pink,
          primaryIconTheme: IconThemeData(color: Colors.black)),
      home: HomePage(title: 'Myapp'),
    );
  }
}

class HomePage extends StatefulWidget {
  HomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _HomePageState createState() => _HomePageState();
}

PageController pageController;

class _HomePageState extends State<HomePage> {
  int _page = 0;
  bool triedSilentLogin = false;
  bool setupNotifications = false;

  Scaffold buildLoginPage() {
    return Scaffold(
      body: Center(
        child: Padding(
          padding: const EdgeInsets.only(top: 240.0),
          child: Column(
            children: <Widget>[
              Text(
                'MyApp',
                style: TextStyle(
                    fontSize: 60.0,
                    fontFamily: "Billabong",
                    color: Colors.black),
              ),
              Padding(padding: const EdgeInsets.only(bottom: 100.0)),
              GestureDetector(
                onTap: login,
                child: Image.asset(
                  "assets/images/google_signin_button.png",
                  width: 225.0,
                ),
              )
            ],
          ),
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    if (triedSilentLogin == false) {
      silentLogin(context);
    }

    if (setupNotifications == false && currentUserModel != null) {
      setUpNotifications();
    }

    return (googleSignIn.currentUser == null || currentUserModel == null)
        ? buildLoginPage()
        : Scaffold(
            body: PageView(
              children: [
                Container(
                  color: Colors.white,
                  child: Feed(),
                ),
                Container(color: Colors.white, child: SearchPage()),
                Container(
                  color: Colors.white,
                  child: Uploader(),
                ),
                Container(
                    color: Colors.white, child: ActivityFeedPage()),
                Container(
                    color: Colors.white,
                    child: ProfilePage(
                      userId: googleSignIn.currentUser.id,
                    )),
              ],
              controller: pageController,
              physics: NeverScrollableScrollPhysics(),
              onPageChanged: onPageChanged,
            ),
            bottomNavigationBar: CupertinoTabBar(
              backgroundColor: Colors.white,
              items: <BottomNavigationBarItem>[
                BottomNavigationBarItem(
                    icon: Icon(Icons.home,
                        color: (_page == 0) ? Colors.black : Colors.grey),
                    title: Container(height: 0.0),
                    backgroundColor: Colors.white),
                BottomNavigationBarItem(
                    icon: Icon(Icons.search,
                        color: (_page == 1) ? Colors.black : Colors.grey),
                    title: Container(height: 0.0),
                    backgroundColor: Colors.white),
                BottomNavigationBarItem(
                    icon: Icon(Icons.add_circle,
                        color: (_page == 2) ? Colors.black : Colors.grey),
                    title: Container(height: 0.0),
                    backgroundColor: Colors.white),
                BottomNavigationBarItem(
                    icon: Icon(Icons.star,
                        color: (_page == 3) ? Colors.black : Colors.grey),
                    title: Container(height: 0.0),
                    backgroundColor: Colors.white),
                BottomNavigationBarItem(
                    icon: Icon(Icons.person,
                        color: (_page == 4) ? Colors.black : Colors.grey),
                    title: Container(height: 0.0),
                    backgroundColor: Colors.white),
              ],
              onTap: navigationTapped,
              currentIndex: _page,
            ),
          );
  }

  void login() async {
    await _ensureLoggedIn(context);
    setState(() {
      triedSilentLogin = true;
    });
  }

  void setUpNotifications() {
    _setUpNotifications();
    setState(() {
      setupNotifications = true;
    });
  }

  void silentLogin(BuildContext context) async {
    await _silentLogin(context);
    setState(() {
      triedSilentLogin = true;
    });
  }

  void navigationTapped(int page) {
    //Animating Page
    pageController.jumpToPage(page);
  }

  void onPageChanged(int page) {
    setState(() {
      this._page = page;
    });
  }

  @override
  void initState() {
    super.initState();
    pageController = PageController();
  }

  @override
  void dispose() {
    super.dispose();
    pageController.dispose();
  }
}

和我的 user.dart：

class Users {
  final String email;
  final String id;
  final String photoUrl;
  final String username;
  final String displayName;
  final String bio;
  final Map followers;
  final Map following;

  const Users(
      {this.username,
      this.id,
      this.photoUrl,
      this.email,
      this.displayName,
      this.bio,
      this.followers,
      this.following});

  factory Users.fromDocument(DocumentSnapshot doc) {
    return Users(
      id: doc.id,
      username: doc.data()['username'],
      email: doc.data()['email'],
      photoUrl: doc.data()['photoUrl'],
      displayName: doc.data()['displayName'],
      bio: doc.data()['bio'],
      followers: doc.data()['followers'],
      following: doc.data()['following'],
    );
  }
}

我认为问题出在 user.dart 文件中的工厂，但我不确定......我还在寻找......谢谢你的帮助

标签： fluttergoogle-cloud-firestore