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Я пытаюсь создать социальное приложение,в котором буду публиковать изображения.Когда я запускаю код, я сталкиваюсь с некоторыми проблемами при извлечении данных из firebase.

 firebase_auth: ^3.1.1
firebase_core: ^1.6.0
google_sign_in: ^5.1.0
firebase_storage: ^10.0.3
cloud_firestore: ^2.5.3
firebase_analytics: ^8.3.2
lottie: ^1.1.0
image_picker: ^0.8.4
 

Выше приведены зависимости файлов pubspec.yaml.

 class HomeScreen extends StatefulWidget {
@override
_HomeScreenState createState() => _HomeScreenState();
 }

class _HomeScreenState extends State<HomeScreen> {
int _currentIndex = 0;
final List<Widget> _children = [
 WeCareHomeScreen(),
 WeCareReminder(),
 Feed(),
 Chatroom(),
 Profile(),
 ];

 @override
 void initState() {
 super.initState();
 Provider.of<FirebaseOperations>(context, listen: false)
    .initUserData(context)
    .whenComplete(() {
  setState(() {});
 });
 }

 Widget build(BuildContext context) {
 return Scaffold(
   body: _children[_currentIndex],
   bottomNavigationBar: CurvedNavigationBar(
      index: 0,
      height: 50.0,
      items: <Widget>[
        Icon(
          Icons.home,
          size: 25,
          color: Colors.white,
        ),
        Icon(
          Icons.home,
          size: 25,
          color: Colors.white,
        ),
        Icon(
          Icons.home,
          size: 25,
          color: Colors.white,
        ),
        Icon(
          Icons.home,
          size: 25,
          color: Colors.white,
        ),
        Icon(
          Icons.home,
          size: 25,
          color: Colors.white,
        ),
      ],
      color: Color.fromRGBO(241, 201, 57, 1.0),
      buttonBackgroundColor: Colors.black,
      backgroundColor: Colors.white,
      animationCurve: Curves.easeInOut,
      animationDuration: Duration(milliseconds: 600),
      onTap: (index) {
        setState(() {
          _currentIndex = index;
        });
      }),
      );
         }
        }
 

Выше находится рабочий стол.код файла дротика.

  class Authentication with ChangeNotifier {
 final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
 final GoogleSignIn googleSignIn = GoogleSignIn();
 late String userUid;
 String get getUserUid => userUid;

 Future logIntoAccount(String email, String password) async {
 UserCredential userCredential = await firebaseAuth
    .signInWithEmailAndPassword(email: email, password: password);
 String userUid;
 User? user = userCredential.user;
 userUid = user!.uid;
 print(userUid);
 notifyListeners();
 }

 Future createAccount(String email, String password) async {  
 UserCredential userCredential = await firebaseAuth
    .createUserWithEmailAndPassword(email: email, password: password);

 User? user = userCredential.user;
 userUid = user!.uid;
 print('Created Account Uid => $userUid');
 notifyListeners();
  }

 Future logoutViaEmail() {
  return firebaseAuth.signOut();
 }

Future signInWithGoogle() async {
 final GoogleSignInAccount? googleSignInAccount =
     await googleSignIn.signIn();
 final GoogleSignInAuthentication googleSignInAuthentication =
     await googleSignInAccount!.authentication;
 final AuthCredential authCredential = GoogleAuthProvider.credential(
     accessToken: googleSignInAuthentication.accessToken,
     idToken: googleSignInAuthentication.idToken);

 final UserCredential userCredential =
     await firebaseAuth.signInWithCredential(authCredential);
 final User? user = userCredential.user;
 assert(user!.uid != null);

 userUid = user!.uid;
 print('Google User Uid => $userUid');
 notifyListeners();
  }

 Future signOutWithGoogle() async {
 return googleSignIn.signOut();
 }
  }
 

Above is Authentification.dart file.

 class FirebaseOperations with ChangeNotifier {
late UploadTask imageUploadTask;
late String initUserEmail;
late String initUserImage;
late String initUserName;

String get getInitUserImage => initUserImage;
String get getInitUserName => initUserName; 
String get getInitUserEmail => initUserEmail;

Future uploadUserAvatar(BuildContext context) async {
Reference imageReference = FirebaseStorage.instance.ref().child(
    'userProfileAvatar/${Provider.of<LandingUtils>(context, listen: 
false).getUserAvatar.path}/${TimeOfDay.now()}');
imageUploadTask = imageReference.putFile(
    Provider.of<LandingUtils>(context, listen: false).getUserAvatar);

await imageUploadTask.whenComplete(() {
  print('Image uploaded!');
});
imageReference.getDownloadURL().then((url) {
  Provider.of<LandingUtils>(context, listen: false).userAvatarUrl =
      url.toString();
  print(
      'the user profile avatar url => ${Provider.of<LandingUtils>(context, listen: 
   false).userAvatarUrl}');
  notifyListeners();
    });
  }

   Future createUserCollection(BuildContext context, dynamic data) async {
   return FirebaseFirestore.instance
    .collection('users')
    .doc(Provider.of<Authentication>(context, listen: false).getUserUid)
    .set(data);
   }

  Future initUserData(BuildContext context) async {
  return FirebaseFirestore.instance
    .collection('users')
    .doc(Provider.of<Authentication>(context, listen: false).getUserUid)
    .get()
    .then((doc) {
  print('Fetching user data');

  initUserName = doc.data()!['username'];
  initUserEmail = doc.data()!['useremail'];
  initUserImage = doc.data()!['userimage'];
  print(initUserName);
  print(initUserEmail);
  print(initUserImage);
  notifyListeners();
  });
   }

  Future uploadPostData(String postId, dynamic data) async {
  return FirebaseFirestore.instance.collection('posts').doc(postId).set(data);
 }
  }
 

Above is the firebaseoperations.dart file.
Here once it printed ‘Fetching user Data’ in the console,it is showing ‘Unhandled Exception: Null check operator used on a null value’ error.
Also once the image is uploaded ,instead of printing the url of image, ‘*************’ is printed.
And ‘Unhandled Exception: LateInitializationError: Field ‘initUserName’ has not been initialized.’ is also printed.

It will me more helpful,if anyone pointout my mistakes and give me a solution.

 Unhandled Exception: LateInitializationError: Field 'initUserName' has not been 
initialized.
 .
 .
 .
 I/flutter (18214): Post image uploaded to storage
 I/flutter (18214): Image uploaded
 I/flutter (18214): 
 *************************************************************************************
 *************************************************************************************
 *********************************************
 .
 .
 .
  E/flutter (18214): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: 
  LateInitializationError: Field 'initUserName' has not been initialized.
 

This is how the error looks.

 class ProfileHelpers with ChangeNotifier {
ConstantColors constantColors = ConstantColors();
Widget headerProfile(
  BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
print(snapshot.data);
return SizedBox(
  height: MediaQuery.of(context).size.height * 0.26,
  width: MediaQuery.of(context).size.width,
  child: Row(
    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
    children: [
      Container(
        height: 150.0,
        width: 170.0,
        child: Column(
          children: [
            GestureDetector(
              onTap: () {},
              child: CircleAvatar(
                backgroundColor: constantColors.transparent,
                radius: 38.0,
                backgroundImage: NetworkImage(
                    '${Provider.of<FirebaseOperations> 
         (context).getInitUserImage}'),
              ),
            ),
            Padding(
              padding: const EdgeInsets.only(top: 8.0),
              child: Text(
                'Vijay',
                //snapshot.data?['username'],
                //snapshot.data!.data()['username'],
                style: TextStyle(
                    color: constantColors.whiteColor,
                    fontWeight: FontWeight.bold,
                    fontSize: 20.0),
              ),
            ),
            Padding(
              padding: const EdgeInsets.only(top: 8.0),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  Icon(EvaIcons.email,
                      color: constantColors.greenColor, size: 16),
                  Padding(
                    padding: const EdgeInsets.only(left: 8.0),
                    child: Text(
                      'username@gmail.com',
                      // snapshot.data!.get('useremail'),
                      style: TextStyle(
                          color: constantColors.whiteColor,
                          fontWeight: FontWeight.bold,
                          fontSize: 12.0),
                    ),
                  ),
                ],
              ),
                 )
               ],
              ),
             ),
      
 

Above is the profile page code.

 enter code here
  
class FeedHelpers with ChangeNotifier {
  ConstantColors constantColors = ConstantColors();
  Widget appBar(BuildContext context) {
  return AppBar(
  backgroundColor: constantColors.darkColor.withOpacity(0.6),
  centerTitle: true,
  actions: [
    IconButton(
        icon: Icon(Icons.camera_enhance_rounded,
            color: constantColors.greenColor),
        onPressed: () {
          Provider.of<UploadPost>(context, listen: false)
              .selectPostImageType(context);
        })
  ],
  title: RichText(
    text: TextSpan(
        text: 'Social ',
        style: TextStyle(
          color: constantColors.whiteColor,
          fontWeight: FontWeight.bold,
          fontSize: 20.0,
        ),
        children: <TextSpan>[
          TextSpan(
              text: 'Feed',
              style: TextStyle(
                color: constantColors.blueColor,
                fontWeight: FontWeight.bold,
                fontSize: 20.0,
              ))
        ]),
         ),
        );
      }

     Widget feedBody(BuildContext context) {
     return SingleChildScrollView(
     child: Padding(
      padding: const EdgeInsets.only(top: 8.0),
      child: Container(
      child: StreamBuilder<QuerySnapshot<Map<String, dynamic>>>(
        stream: 
       FirebaseFirestore.instance.collection('posts').snapshots(),
        builder: (BuildContext context,
            AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>> 
         snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting) 
            {
            return Center(
              child: SizedBox(
                height: 500.0,
                width: 400.0,
                child: 
           Lottie.asset('assets/animations/loading.json'),
              ),
            );
          } else {
            return loadPosts(context, snapshot);
          }
        },
      ),
      height: MediaQuery.of(context).size.height,
      width: MediaQuery.of(context).size.width,
      decoration: BoxDecoration(
          color: constantColors.darkColor.withOpacity(0.6),
          borderRadius: BorderRadius.only(
              topLeft: Radius.circular(18.0),
              topRight: Radius.circular(18.0))),
    ),
  ),
    );
   }

   Widget loadPosts(
  BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
  return ListView(
     children: snapshot.data!.docs.map((DocumentSnapshot 
  documentSnapshot) {
  Map<String, dynamic> data =
      documentSnapshot.data()! as Map<String, dynamic>;
  return Container(
    height: MediaQuery.of(context).size.height * 0.62,
    width: MediaQuery.of(context).size.width,
    child: Column(
      mainAxisAlignment: MainAxisAlignment.start,
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Padding(
          padding: const EdgeInsets.only(top: 8.0, left: 8.0),
          child: Row(
            children: [
              GestureDetector(
                child: CircleAvatar(
                  backgroundColor: constantColors.blueGreyColor,
                  radius: 20.0,
                  backgroundImage: NetworkImage(
                      '${Provider.of<UploadPost> 
                 (context).getUploadPostImage}'),
                  //  NetworkImage(documentSnapshot['userimage']),
                ),
              ),
              Padding(
                padding: const EdgeInsets.only(left: 8.0),
                child: Container(
                  width: MediaQuery.of(context).size.width * 0.6,
                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.start,
                    crossAxisAlignment: CrossAxisAlignment.start,
                    children: [
                      Container(
                          child: RichText(
                        text: TextSpan(
                            text: data['username'],
                            style: TextStyle(
                                color: constantColors.blueColor,
                                fontSize: 14.0,
                                fontWeight: FontWeight.bold),
                            children: <TextSpan>[
                              TextSpan(
                                  text: '  , 12 hours ago',
                                  style: TextStyle(
                                      color: 
                       constantColors.lightColor
                                          .withOpacity(0.8)))
                            ]),
                      )),
                      Container(
                        child: Text(
                          data['username'],
                          style: TextStyle(
                            color: constantColors.greenColor,
                            fontWeight: FontWeight.bold,
                            fontSize: 16.0,
                          ),
                        ),
                      ),
                    ],
                  ),
                ),
              )
            ],
          ),
        ),
        Padding(
          padding: const EdgeInsets.only(top: 8.0),
          child: Container(
              height: MediaQuery.of(context).size.height * 0.46,
              width: MediaQuery.of(context).size.width,
              child: FittedBox(
                  //  child: Image.network(downloadURL.toString()),
                  child: Image.network(data['postimage'], scale: 
        2))),
        ),
        Padding(
          padding: const EdgeInsets.only(top: 8.0),
          child: Padding(
            padding: const EdgeInsets.only(left: 20.0),
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                Container(
                  width: 80.0,
                  child: Row(
                    children: [
                      GestureDetector(
                        child: Icon(
                          FontAwesomeIcons.heart,
                          color: constantColors.redColor,
                          size: 22.0,
                        ),
                      ),
                      Padding(
                        padding: const EdgeInsets.only(left: 8.0),
                        child: Text(
                          '0',
                          style: TextStyle(
                              color: constantColors.whiteColor,
                              fontWeight: FontWeight.bold,
                              fontSize: 18.0),
                        ),
                      )
                    ],
                  ),
                ),
 

Выше приведен файл feed_helper.

 class UploadPost with ChangeNotifier {
TextEditingController captionController = TextEditingController();
ConstantColors constantColors = ConstantColors();
late File uploadPost;
late File uploadPostImage;
File get getUploadPostImage => uploadPostImage;
late String uploadPostImageUrl;
String get getUploadPostImageUrl => uploadPostImageUrl;
final picker = ImagePicker();
late UploadTask imagePostUploadTask;

Future pickUploadPostImage(BuildContext context, ImageSource 
source) async {
final uploadPostImageVal = await picker.pickImage(source: source);
uploadPostImageVal == null
    ? print('Select Image')
    : uploadPostImage = File(uploadPostImageVal.path);
print(uploadPostImageVal!.path);

uploadPostImage != null
    ? showPostImage(context)
    : print('Image upload error');

notifyListeners();
}

 Future uploadPostImageToFirebase() async {
 Reference imageReference = FirebaseStorage.instance
    .ref()
    .child('posts/${uploadPostImage!.path}/${TimeOfDay.now()}');
imagePostUploadTask = imageReference.putFile(uploadPostImage!);
await imagePostUploadTask.whenComplete(() {
  print('Post image uploaded to storage');
});
imageReference.getDownloadURL().then((imageUrl) {
  uploadPostImageUrl = imageUrl;
  print(uploadPostImageUrl);
});
notifyListeners();
 }
 

Вышеуказанный файл является файлом uploadpost.dart

Проблема в том, что вы объявляете initUserName поле как late и пытаетесь получить к нему доступ перед его инициализацией (присвоением ему значения).

late Ключевое слово говорит компилятору не беспокоиться о том, что переменная имеет значение null, потому что вы гарантируете, что присвоите ей значение, прежде чем пытаться получить к ней доступ.

Вы можете либо объявить initUserName как String? initUserName

Таким образом, вы инициализируете его null значением;

В противном случае вы можете убедиться, что задали ему такое значение: FirebaseOperations.initUserName = 'username'; прежде чем пытаться прочитать его значение