Provider.of总是返回null Flutter

如何解决Provider.of总是返回null Flutter

我有一个提供者对象，直到上星期我一直在工作

Flutter channel stable
Flutter upgrade

现在，它始终返回null。

问题出现在我的初始页面上。这是页面的内容：

import 'dart:io';
import 'package:Flutter/cupertino.dart';
import 'package:Flutter/material.dart';
import 'package:boots/helper/enum.dart';
import 'package:boots/helper/theme.dart';
import 'package:boots/page/Auth/selectAuthMethod.dart';
import 'package:boots/page/homePage.dart';
import 'package:boots/state/authState.dart';
import 'package:boots/widgets/customWidgets.dart';
import 'package:provider/provider.dart';

class SplashPage extends StatefulWidget {
  SplashPage({Key key}) : super(key: key);

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

class _SplashPageState extends State<SplashPage> {
  @override
  void initState() {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      timer();
    });
    super.initState();
  }

  void timer() async {
    Future.delayed(Duration(seconds: 1)).then((_) {
      var state = Provider.of<AuthState>(context,listen: false);
      state.getCurrentUser();
    });
  }

  Widget _body() {
    var height = 150.0;
    return Container(
      height: fullHeight(context),width: fullWidth(context),child: Container(
        height: height,width: height,alignment: Alignment.center,child: Container(
          padding: EdgeInsets.all(50),decoration: Boxdecoration(
            color: Colors.white,borderRadius: BorderRadius.all(
              Radius.circular(10),),child: Stack(
            alignment: Alignment.center,children: <Widget>[
              Platform.isIOS
                  ? CupertinoActivityIndicator(
                      radius: 35,)
                  : CircularProgressIndicator(
                      strokeWidth: 2,Image.asset(
                'assets/images/icon-480.png',height: 30,width: 30,)
            ],);
  }

  @override
  Widget build(BuildContext context) {
    var state = Provider.of<AuthState>(context);
    return Scaffold(
      backgroundColor: TwitterColor.white,body: state.authStatus == AuthStatus.NOT_DETERmineD
          ? _body()
          : state.authStatus == AuthStatus.NOT_LOGGED_IN
              ? WelcomePage()
              : HomePage(),);
  }
}

这是罪魁祸首：

  void timer() async {
    Future.delayed(Duration(seconds: 1)).then((_) {
      var state = Provider.of<AuthState>(context,listen: false);
      state.getCurrentUser();
    });
  }

我的main.dart是我为AuthState设置ChangeNotifierProvider的地方，看起来像：

import 'package:boots/blocs/place_bloc.dart';
import 'package:boots/helper/locator.dart';
import 'package:boots/state/communitiesstate.dart';
import 'package:boots/state/mapState.dart';
import 'package:Flutter/material.dart';
import 'package:boots/helper/theme.dart';
import 'package:boots/state/searchState.dart';
import 'package:boots/state/nearbyState.dart';
import 'package:Flutter/services.dart';
import 'helper/routes.dart';
import 'state/appState.dart';
import 'package:provider/provider.dart';
import 'state/authState.dart';
import 'state/chats/chatState.dart';
import 'state/FeedState.dart';
import 'package:google_fonts/google_fonts.dart';
import 'state/notificationState.dart';

void main() {
  setupLocator();
  WidgetsFlutterBinding.ensureInitialized();

  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    SystemChrome.setsystemUIOverlayStyle(
        systemUIOverlayStyle(statusBarColor: AppColor.primary));
    return MultiProvider(
      providers: [
        ChangeNotifierProvider<AppState>(create: (_) => AppState()),ChangeNotifierProvider<AuthState>(create: (_) => AuthState()),ChangeNotifierProvider<FeedState>(create: (_) => FeedState()),ChangeNotifierProvider<ChatState>(create: (_) => ChatState()),ChangeNotifierProvider<SearchState>(create: (_) => SearchState()),ChangeNotifierProvider<NotificationState>(
            create: (_) => NotificationState()),ChangeNotifierProvider<MapState>(create: (_) => MapState()),ChangeNotifierProvider<Communitiesstate>(
            create: (_) => Communitiesstate()),ChangeNotifierProvider<NearbyState>(create: (_) => NearbyState()),ChangeNotifierProvider<PlaceBloc>(create: (_) => PlaceBloc()),],child: MaterialApp(
        title: 'Boots',theme: AppTheme.apptheme.copyWith(
          textTheme: GoogleFonts.muliTextTheme(
            Theme.of(context).textTheme,debugShowCheckedModeBanner: false,routes: Routes.route(),// goes to splash.dart
        onGenerateRoute: (settings) => Routes.onGenerateRoute(settings),onUnkNownRoute: (settings) => Routes.onUnkNownRoute(settings),);
  }
}

最后，我的AuthState类如下：

import 'dart:io';

import 'package:firebase_auth/firebase_auth.dart' as firebaseauth;
import 'package:firebase_database/firebase_database.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:firebase_storage/firebase_storage.dart';
import 'package:Flutter/material.dart';
import 'package:Flutter/services.dart';
import 'package:boots/helper/enum.dart';
import 'package:boots/helper/utility.dart';
import 'package:boots/model/user.dart';
import 'package:boots/widgets/customWidgets.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'package:path/path.dart' as Path;
import 'appState.dart';
import 'package:firebase_database/firebase_database.dart' as dabase;

class AuthState extends AppState {
  AuthStatus authStatus = AuthStatus.NOT_DETERmineD;
  bool isSignInWithGoogle = false;
  firebaseauth.User user;
  String userId;
  final FirebaseMessaging _firebaseMessaging = FirebaseMessaging();
  final firebaseauth.FirebaseAuth _firebaseAuth =
      firebaseauth.FirebaseAuth.instance;
  final GoogleSignIn _googleSignIn = GoogleSignIn();
  dabase.Query _profileQuery;
  List<User> _profileusermodelList;
  User _usermodel;

  User get usermodel => _usermodel;

  User get profileusermodel {
    if (_profileusermodelList != null && _profileusermodelList.length > 0) {
      return _profileusermodelList.last;
    } else {
      return null;
    }
  }

  void removeLastUser() {
    _profileusermodelList.removeLast();
  }

  /// logout from device
  void logoutCallback() {
    authStatus = AuthStatus.NOT_LOGGED_IN;
    userId = '';
    _usermodel = null;
    user = null;
    _profileusermodelList = null;
    if (isSignInWithGoogle) {
      _googleSignIn.signOut();
      logEvent('google_logout');
    }
    _firebaseAuth.signOut();
    notifyListeners();
  }

  /// Alter select auth method,login and sign up page
  void openSignUpPage() {
    authStatus = AuthStatus.NOT_LOGGED_IN;
    userId = '';
    notifyListeners();
  }

  databaseInit() {
    try {
      if (_profileQuery == null) {
        _profileQuery = kDatabase.child("profile").child(user.uid);
        _profileQuery.onValue.listen(_onProfileChanged);
      }
    } catch (error) {
      cprint(error,errorIn: 'databaseInit');
    }
  }

  /// Verify user's credentials for login
  Future<String> signIn(String email,String password,{GlobalKey<ScaffoldState> scaffoldKey}) async {
    try {
      loading = true;
      var result = await _firebaseAuth.signInWithEmailAndPassword(
          email: email,password: password);
      user = result.user;
      userId = user.uid;
      return user.uid;
    } catch (error) {
      loading = false;
      cprint(error,errorIn: 'signIn');
      kAnalytics.logLogin(loginMethod: 'email_login');
      customSnackBar(scaffoldKey,error.message);
      // logoutCallback();
      return null;
    }
  }

  /// Create user from `google login`
  /// If user is new then it create a new user
  /// If user is old then it just `authenticate` user and return firebase user data
  Future<firebaseauth.User> handleGoogleSignIn() async {
    try {
      /// Record log in firebase kAnalytics about Google login
      kAnalytics.logLogin(loginMethod: 'google_login');
      final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
      if (googleUser == null) {
        throw Exception('Google login cancelled by user');
      }
      final GoogleSignInAuthentication googleAuth =
          await googleUser.authentication;

      final firebaseauth.AuthCredential credential =
          firebaseauth.GoogleAuthProvider.credential(
        accesstoken: googleAuth.accesstoken,idToken: googleAuth.idToken,);
      user = (await _firebaseAuth.signInWithCredential(credential)).user;
      authStatus = AuthStatus.LOGGED_IN;
      userId = user.uid;
      isSignInWithGoogle = true;
      createuserFromGoogleSignIn(user);
      notifyListeners();
      return user;
    } on PlatformException catch (error) {
      user = null;
      authStatus = AuthStatus.NOT_LOGGED_IN;
      cprint(error,errorIn: 'handleGoogleSignIn');
      return null;
    } on Exception catch (error) {
      user = null;
      authStatus = AuthStatus.NOT_LOGGED_IN;
      cprint(error,errorIn: 'handleGoogleSignIn');
      return null;
    } catch (error) {
      user = null;
      authStatus = AuthStatus.NOT_LOGGED_IN;
      cprint(error,errorIn: 'handleGoogleSignIn');
      return null;
    }
  }

  /// Create user profile from google login
  createuserFromGoogleSignIn(firebaseauth.User user) {
    var diff = DateTime.Now().difference(user.Metadata.creationTime);
    // Check if user is new or old
    // If user is new then add new user to firebase realtime kDatabase
    if (diff < Duration(seconds: 15)) {
      User model = User(
        bio: 'Edit profile to update bio',dob: DateTime(1950,DateTime.Now().month,DateTime.Now().day + 3)
            .toString(),location: 'Somewhere in universe',profilePic: user.photoURL,displayName: user.displayName,email: user.email,key: user.uid,userId: user.uid,contact: user.phoneNumber,isverified: user.emailVerified,);
      createuser(model,newUser: true);
    } else {
      cprint('Last login at: ${user.Metadata.lastSignInTime}');
    }
  }

  /// Create new user's profile in db
  Future<String> signUp(User usermodel,{GlobalKey<ScaffoldState> scaffoldKey,String password}) async {
    try {
      loading = true;
      var result = await _firebaseAuth.createuserWithEmailAndPassword(
        email: usermodel.email,password: password,);

      user = result.user;
      authStatus = AuthStatus.LOGGED_IN;
      kAnalytics.logSignUp(signUpMethod: 'register');

      await result.user.updateProfile(
        displayName: usermodel.displayName,photoURL: usermodel.profilePic,);
      _usermodel = usermodel;
      _usermodel.key = user.uid;
      _usermodel.userId = user.uid;
      createuser(_usermodel,newUser: true);
      return user.uid;
    } catch (error) {
      loading = false;
      cprint(error,errorIn: 'signUp');
      customSnackBar(scaffoldKey,error.message);
      return null;
    }
  }

  /// `Create` and `Update` user
  /// IF `newUser` is true new user is created
  /// Else existing user will update with new values
  createuser(User user,{bool newUser = false}) {
    if (newUser) {
      // Create username by the combination of name and id
      user.userName = getUserName(email: user.email);
      kAnalytics.logEvent(name: 'create_newUser');

      // Time at which user is created
      user.createdAt = DateTime.Now().toUtc().toString();
    }

    kDatabase.child('profile').child(user.userId).set(user.toJsonUpdate());
    _usermodel = user;
    if (_profileusermodelList != null) {
      _profileusermodelList.last = _usermodel;
    }
    loading = false;
  }

  /// Fetch current user profile
  Future<firebaseauth.User> getCurrentUser() async {
    try {
      loading = true;
      logEvent('get_currentUSer');
      user = _firebaseAuth != null ? _firebaseAuth.currentUser : null;
      if (user != null) {
        authStatus = AuthStatus.LOGGED_IN;
        userId = user.uid;
        getProfileUser();
      } else {
        authStatus = AuthStatus.NOT_LOGGED_IN;
      }
      loading = false;
      return user;
    } catch (error) {
      loading = false;
      cprint(error,errorIn: 'getCurrentUser');
      authStatus = AuthStatus.NOT_LOGGED_IN;
      return null;
    }
  }

  /// Reload user to get refresh user data
  reloadUser() async {
    await user.reload();
    user = _firebaseAuth.currentUser;
    if (user.emailVerified) {
      usermodel.isverified = true;
      // If user verifed his email
      // Update user in firebase realtime kDatabase
      createuser(usermodel);
      cprint('User email verification complete');
      logEvent('email_verification_complete',parameter: {usermodel.userName: user.email});
    }
  }

  /// Send email verification link to email2
  Future<void> sendEmailVerification(
      GlobalKey<ScaffoldState> scaffoldKey) async {
    firebaseauth.User user = _firebaseAuth.currentUser;
    user.sendEmailVerification().then((_) {
      logEvent('email_verifcation_sent',parameter: {usermodel.displayName: user.email});
      customSnackBar(
        scaffoldKey,'An email verification link is send to your email.',);
    }).catchError((error) {
      cprint(error.message,errorIn: 'sendEmailVerification');
      logEvent('email_verifcation_block',error.message,);
    });
  }

  /// Check if user's email is verified
  Future<bool> isEmailVerified() async {
    firebaseauth.User user = _firebaseAuth.currentUser;
    return user.emailVerified;
  }

  /// Send password reset link to email
  Future<void> forgetpassword(String email,{GlobalKey<ScaffoldState> scaffoldKey}) async {
    try {
      await _firebaseAuth.sendPasswordResetEmail(email: email).then((value) {
        customSnackBar(scaffoldKey,'A reset password link is sent yo your mail.You can reset your password from there');
        logEvent('forgot+password');
      }).catchError((error) {
        cprint(error.message);
        return false;
      });
    } catch (error) {
      customSnackBar(scaffoldKey,error.message);
      return Future.value(false);
    }
  }

  /// `Update user` profile
  Future<void> updateUserProfile(User usermodel,{File image}) async {
    try {
      if (image == null) {
        createuser(usermodel);
      } else {
        Reference storageReference = FirebaseStorage.instance
            .ref()
            .child('user/profile/${Path.basename(image.path)}');
        UploadTask uploadTask = storageReference.putFile(image);
        await uploadTask.then((value) {
          storageReference.getDownloadURL().then((fileURL) async {
            print(fileURL);
            await user.updateProfile(
              displayName: usermodel?.displayName ?? user.displayName,photoURL: fileURL,);
            if (usermodel != null) {
              usermodel.profilePic = fileURL;
              createuser(usermodel);
            } else {
              _usermodel.profilePic = fileURL;
              createuser(_usermodel);
            }
          });
        });
      }
      logEvent('update_user');
    } catch (error) {
      cprint(error,errorIn: 'updateUserProfile');
    }
  }

  /// `Fetch` user `detail` whoose userId is passed
  Future<User> getuserDetail(String userId) async {
    User user;
    var snapshot = await kDatabase.child('profile').child(userId).once();
    if (snapshot.value != null) {
      var map = snapshot.value;
      user = User.fromJson(map);
      user.key = snapshot.key;
      return user;
    } else {
      return null;
    }
  }

  /// Fetch user profile
  /// If `userProfileId` is null then logged in user's profile will fetched
  getProfileUser({String userProfileId}) {
    try {
      loading = true;
      if (_profileusermodelList == null) {
        _profileusermodelList = [];
      }

      userProfileId = userProfileId == null ? user.uid : userProfileId;
      kDatabase
          .child("profile")
          .child(userProfileId)
          .once()
          .then((DataSnapshot snapshot) {
        if (snapshot.value != null) {
          var map = snapshot.value;
          if (map != null) {
            _profileusermodelList.add(User.fromJson(map));
            if (userProfileId == user.uid) {
              _usermodel = _profileusermodelList.last;
              _usermodel.isverified = user.emailVerified;
              if (!user.emailVerified) {
                // Check if logged in user verified his email address or not
                reloadUser();
              }
              if (_usermodel.fcmToken == null) {
                updateFCMToken();
              }
            }

            logEvent('get_profile');
          }
        }
        loading = false;
      });
    } catch (error) {
      loading = false;
      cprint(error,errorIn: 'getProfileUser');
    }
  }

  /// if firebase token not available in profile
  /// Then get token from firebase and save it to profile
  /// When someone sends you a message FCM token is used
  void updateFCMToken() {
    if (_usermodel == null) {
      return;
    }
    getProfileUser();
    _firebaseMessaging.getToken().then((String token) {
      assert(token != null);
      _usermodel.fcmToken = token;
      createuser(_usermodel);
    });
  }

  /// Follow / Unfollow user
  ///
  /// If `removeFollower` is true then remove user from follower list
  ///
  /// If `removeFollower` is false then add user to follower list
  followUser({bool removeFollower = false}) {
    /// `usermodel` is user who is looged-in app.
    /// `profileusermodel` is user whoose profile is open in app.
    try {
      if (removeFollower) {
        /// If logged-in user `alredy follow `profile user then
        /// 1.Remove logged-in user from profile user's `follower` list
        /// 2.Remove profile user from logged-in user's `following` list
        profileusermodel.followersList.remove(usermodel.userId);

        /// Remove profile user from logged-in user's following list
        usermodel.followingList.remove(profileusermodel.userId);
        cprint('user removed from following list',event: 'remove_follow');
      } else {
        /// if logged in user is `not following` profile user then
        /// 1.Add logged in user to profile user's `follower` list
        /// 2. Add profile user to logged in user's `following` list
        if (profileusermodel.followersList == null) {
          profileusermodel.followersList = [];
        }
        profileusermodel.followersList.add(usermodel.userId);
        // Adding profile user to logged-in user's following list
        if (usermodel.followingList == null) {
          usermodel.followingList = [];
        }
        usermodel.followingList.add(profileusermodel.userId);
      }
      // update profile user's user follower count
      profileusermodel.followers = profileusermodel.followersList.length;
      // update logged-in user's following count
      usermodel.following = usermodel.followingList.length;
      kDatabase
          .child('profile')
          .child(profileusermodel.userId)
          .child('followerList')
          .set(profileusermodel.followersList);
      kDatabase
          .child('profile')
          .child(usermodel.userId)
          .child('followingList')
          .set(usermodel.followingList);
      cprint('user added to following list',event: 'add_follow');
      notifyListeners();
    } catch (error) {
      cprint(error,errorIn: 'followUser');
    }
  }

  /// Trigger when logged-in user's profile change or updated
  /// Firebase event callback for profile update
  void _onProfileChanged(Event event) {
    if (event.snapshot != null) {
      final updatedUser = User.fromJson(event.snapshot.value);
      if (updatedUser.userId == user.uid) {
        _usermodel = updatedUser;
      }
      cprint('User Updated');
      notifyListeners();
    }
  }
}

这些是我做的日志

Flutter clean

之后

Flutter run --release

日志：

I/Flutter (13941): 
E/Flutter (13941): [ERROR:Flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: NoSuchMethodError: The method 'getCurrentUser' was called on null.
E/Flutter (13941): Receiver: null
E/Flutter (13941): Tried calling: getCurrentUser()
E/Flutter (13941): #0      _SplashPageState.timer.<anonymous closure> (package:boots/page/common/splash.dart:31)
E/Flutter (13941): #1      _rootRunUnary (dart:async/zone.dart:1198)
E/Flutter (13941): #2      _CustomZone.runUnary (dart:async/zone.dart:1100)
E/Flutter (13941): #3      _FutureListener.handleValue (dart:async/future_impl.dart:143)
E/Flutter (13941): #4      Future._propagatetoListeners.handleValueCallback (dart:async/future_impl.dart:696)
E/Flutter (13941): #5      Future._propagatetoListeners (dart:async/future_impl.dart:725)
E/Flutter (13941): #6      Future._complete (dart:async/future_impl.dart:519)
E/Flutter (13941): #7      new Future.delayed.<anonymous closure> (dart:async/future.dart:323)
E/Flutter (13941): #8      _rootRun (dart:async/zone.dart:1182)
E/Flutter (13941): #9      _CustomZone.run (dart:async/zone.dart:1093)
E/Flutter (13941): #10     _CustomZone.runGuarded (dart:async/zone.dart:997)
E/Flutter (13941): #11     _CustomZone.bindCallbackGuarded.<anonymous closure> (dart:async/zone.dart:1037)
E/Flutter (13941): #12     _rootRun (dart:async/zone.dart:1190)
E/Flutter (13941): #13     _CustomZone.run (dart:async/zone.dart:1093)
E/Flutter (13941): #14     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:1021)
E/Flutter (13941): #15     TickerFuture.whenCompleteOrCancel.thunk (package:Flutter/src/scheduler/ticker.dart:399)
E/Flutter (13941): #16     _Timer._runTimers (dart:isolate-patch/timer_impl.dart:397)
E/Flutter (13941): #17     _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:428)
E/Flutter (13941): #18     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168)
E/Flutter (13941):

由于我的应用程序因此无法再启动，因此我想纠正此问题。感谢所有帮助！

解决方法

结果是我的更新导致需要添加新的firebase依赖项。

在pubspec.yaml中，必须添加：

df <- structure(list(organisms = structure(1:3,.Label = c("A","B","C"),class = "factor"),indicator_value = c(0.98,0.98,0.98
),R_G1 = c(1,0.05,0.02),p_G1 = c(0.05,NA,R_G2 = c(0.2,0.1,0.07),p_G2 = c(5L,3L,NA),R_G3 = c(0.09,0.09,0.2),p_G3 = c(0.02,0.04,0.02)),class = "data.frame",row.names = c(NA,-3L))

df
#>   organisms indicator_value R_G1 p_G1 R_G2 p_G2 R_G3 p_G3
#> 1         A            0.98 1.00 0.05 0.20    5 0.09 0.02
#> 2         B            0.98 0.05   NA 0.10    3 0.09 0.04
#> 3         C            0.98 0.02 0.02 0.07   NA 0.20 0.02

主要是必须添加

firebase_core: ^0.5.2

就在

之前

await Firebase.initializeApp();