I am trying to list some data from a firestore database. While pulling the data I got this exception:

======== Exception caught by provider ==============================================================
The following assertion was thrown:
An exception was throw by _MapStream<QuerySnapshot<Map<String, dynamic>>, List<UserModel>?> listened by

StreamProvider<List<UserModel>?>, but no `catchError` was provided.

Exception:
type 'int' is not a subtype of type 'double?'

====================================================================================================

These are my database functions:

  // users list from snapshot
  List<UserModel>? _usersListFromSnapshot(QuerySnapshot snapshot) {
    return snapshot.docs.map((doc) {
      return UserModel(
        uid: doc.get('uid'),
        username: doc.get('username') ?? '',
        email: doc.get('email') ?? '',
        type: doc.get('type') ?? '',
        balance: doc.get('balance'),
        usertag: doc.get('usertag') ?? '',
        connected: doc.get('connected') ?? '',
      );
    }).toList();
  }

  // get users stream
  Stream<List<UserModel>?> get usersList {
    User? user = _auth.currentUser;
    UserModel? userModel = _userFromFirebaseUser(user);
    final CollectionReference userRef = FirebaseFirestore.instance.collection("users");
    final List? connectedList = userModel?.connected;
    final Query inList = userRef.where('uid', whereIn: connectedList);
    return inList.snapshots().map(_usersListFromSnapshot);
  }

This is my user.dart:

class UserModel {
  String? uid;
  String? username;
  String? email;
  String? type;
  double? balance;
  String? usertag;
  List<dynamic>? connected;

  UserModel({this.uid, this.username, this.email, this.type, this.balance, this.usertag, this.connected});

  // receive data from the server
  factory UserModel.fromMap(map) {
    return UserModel(
      uid: map['uid'],
      username: map['username'],
      email: map['email'],
      type: map['type'],
      balance: map['balance'],
      usertag: map['usertag'],
      connected: map['connected']
    );
  }

  // send data to the server
  Map<String, dynamic> toMap() {
    return {
      'uid': uid,
      'username': username,
      'email': email,
      'type': type,
      'balance': balance,
      'usertag': usertag,
      'connected': connected,
    };
  }
}

This is my Listbuilder:

class ConnectedScreen extends StatefulWidget {
  const ConnectedScreen({Key? key}) : super(key: key);

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

class _ConnectedScreenState extends State<ConnectedScreen> {

  User? user = FirebaseAuth.instance.currentUser;
  UserModel userModel = UserModel();

  @override
  void initState() {
    super.initState();
    FirebaseFirestore.instance
        .collection('users')
        .doc(user!.uid)
        .get()
        .then((value) {
      userModel = UserModel.fromMap(value.data());
      setState(() {});
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: customAppBar("Connect Users", "back", ""),
      body: Padding(
        padding: EdgeInsets.all(8.0),
        child: SingleChildScrollView(
          child: StreamProvider<List<UserModel>?>.value(
            value: AuthService().usersList,
            initialData: [],
            child: ConnectedListBuilder(),
          ),
        ),
      ),
    );
  }
}


class ConnectedListBuilder extends StatefulWidget {
  const ConnectedListBuilder({Key? key}) : super(key: key);

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

class _ConnectedListBuilderState extends State<ConnectedListBuilder> {
  @override
  Widget build(BuildContext context) {

    final connectedUsers = Provider.of<List<UserModel>?>(context);

    if (connectedUsers!.isNotEmpty) {
      return Padding(
        padding: EdgeInsets.only(top: 8.0),
        child: ListView.builder(
          itemCount: connectedUsers.length,
          itemBuilder: (context, index) {
            return ConnectedUserTile(userModel: connectedUsers[index]);
          },
        ),
      );
    } else if (connectedUsers.isEmpty) {
      return Text("List is empty");
    }
    return Center(
      child: CircularProgressIndicator(),
    );
  }
}


class ConnectedUserTile extends StatelessWidget {

  final UserModel? userModel;

  const ConnectedUserTile({Key? key, required this.userModel}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.all(8.0),
      child: Card(
        margin: EdgeInsets.fromLTRB(20, 6, 20, 0),
        child: ListTile(
          leading: CircleAvatar(
            backgroundImage: NetworkImage('https://picsum.photos/100'),
            radius: 25,
          ),
          title: Text(
            "${userModel!.username}",
            style: TextStyle(
              color: Colors.black54,
              fontSize: 18,
              fontWeight: FontWeight.bold,
            ),
          ),
          subtitle: Text(
            "${userModel!.usertag}",
            style: TextStyle(
              color: Colors.black38,
              fontSize: 14,
            ),
          ),
        ),
      ),
    );
  }
}

What's interesting is that this exact code works for another ListView, so I don't think it's an error with the database functions, but I´m out of ideas how to try fixing it. I also didn't find much helpful information on the internet about this, so I would be very thankful for any help.

CodePudding user response：

Looks like the issue is in parsing the balance field. In the instances that it works, the balance was probably formatted as a double, e.g. "1.23" and so when it's converted to a map, it's converted as a double, which is a subtype of double?.

When it's not working, it's most likely dealing with an integer balance, like "25" - The value stored in the map will then have a type of int, which is not a subtype of double?, because int is not a subtype of double.

To fix this, you can simply ensure that you're always dealing with a double, by calling toDouble() on the value.

// receive data from the server
factory UserModel.fromMap(map) {
  return UserModel(
    uid: map['uid'],
    username: map['username'],
    email: map['email'],
    type: map['type'],
    balance: map['balance'].toDouble(), // <- Change this line
    usertag: map['usertag'],
    connected: map['connected']
  );
}