CODEWITHSUNDEEP
firebaseflutterfirebase-authentication
user18124547
user18124547

Reputation:

flutter got error code. _CastError (Null check operator used on a null value)

Update context

Can I use where and orderby in FirebaseFirestore to running? Because I got the error in itemCount: snapshot.data!.docs.length when I use this code on below...

enter image description here

body: StreamBuilder(
        stream: FirebaseFirestore.instance
            .collection('Posts')
            .where('country', isEqualTo: '${user.country}')
            //.where('country', isEqualTo: 'Australia')
            .orderBy('time', descending: true) 
            .snapshots(),
        builder: (context,
            AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>> snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Center(
              child: CircularProgressIndicator(),
            );
          }
          return ListView.builder(
            itemCount: snapshot.data!.docs.length,
            itemBuilder: (context, index) => Container(
              margin: EdgeInsets.symmetric(
                  horizontal: width > webScreenSize ? width * 0.3 : 0,
                  vertical: width > webScreenSize ? 15 : 0),
              child: PostCard(
                snap: snapshot.data!.docs[index],
              ),
            ),
          );
        },
      ),

So...where has problem? when I mark the .where('country', isEqualTo: '${user.country}') it's working, but can't use both...

Update context

When I want to get data from firebase, I tried to used this methods, but I get a error code _CastError (Null check operator used on a null value).

User get getUser => _user!;

enter image description here

If I mark .where('country', isEqualTo: '${user.country}') or .orderBy('time', descending: true), it was working, but they can't appear at the same time.

So how can do use both?

class _FeedScreenState extends State<FeedScreen> {
  @override
  Widget build(BuildContext context) {
    final width = MediaQuery.of(context).size.width;
    final User user = Provider.of<UserProvider>(context).getUser;
    return Scaffold(
body: StreamBuilder(
        stream: FirebaseFirestore.instance
            .collection('Posts')
            .where('country', isEqualTo: '${user.country}')
            .orderBy('time', descending: true)
            .snapshots(),
        builder: (context,
            AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>> snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Center(
              child: CircularProgressIndicator(),
            );
          }
          return ListView.builder(
            itemCount: snapshot.data!.docs.length,
            itemBuilder: (context, index) => Container(
              margin: EdgeInsets.symmetric(
                  horizontal: width > webScreenSize ? width * 0.3 : 0,
                  vertical: width > webScreenSize ? 15 : 0),
              child: PostCard(
                snap: snapshot.data!.docs[index],
              ),
            ),
          );
        },
      ),

UserProvider.dart

class UserProvider with ChangeNotifier {
  User? _user;
  final AuthMethods _authMethods = AuthMethods();

  User get getUser => _user!;

  Future<void> refreshUser() async {
    User user = await _authMethods.getUserDetails();
    _user = user;
    notifyListeners();
  }
}

Upvotes: 0

Views: 396

Answers (1)

Frank nike
Frank nike

Reputation: 388

You're not updating _user.

You need to call
Provider.of<UserProvider>(context).refreshUser() at least i think that's how you use provider.

So it should be

    final width =  MediaQuery.of(context).size.width;
    Provider.of<UserProvider>(context).refreshUser();
    final User user = Provider.of<UserProvider>(context).getUser;

That should update/set the value of _user

Upvotes: 0

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