The first thing we need to do in this class is to initialize our database.

.../image.png
.../Mx/image.png
.../Nx/image.png
...etc.

import 'dart:io';

import 'package:mqtt_client/mqtt_client.dart';
import 'package:mqtt_client/mqtt_server_client.dart';

class MQTTClientManager {
  MqttServerClient client =
      MqttServerClient.withPort('10.0.2.2', 'mobile_client', 1883);

  Future<int> connect() async {
    client.logging(on: true);
    client.keepAlivePeriod = 60;
    client.onConnected = onConnected;
    client.onDisconnected = onDisconnected;
    client.onSubscribed = onSubscribed;
    client.pongCallback = pong;

    final connMessage =
        MqttConnectMessage().startClean().withWillQos(MqttQos.atLeastOnce);
    client.connectionMessage = connMessage;

    try {
      await client.connect();
    } on NoConnectionException catch (e) {
      print('MQTTClient::Client exception - $e');
      client.disconnect();
    } on SocketException catch (e) {
      print('MQTTClient::Socket exception - $e');
      client.disconnect();
    }

    return 0;
  }

  void disconnect(){
    client.disconnect();
  }

  void subscribe(String topic) {
    client.subscribe(topic, MqttQos.atLeastOnce);
  }

  void onConnected() {
    print('MQTTClient::Connected');
  }

  void onDisconnected() {
    print('MQTTClient::Disconnected');
  }

  void onSubscribed(String topic) {
    print('MQTTClient::Subscribed to topic: $topic');
  }

  void pong() {
    print('MQTTClient::Ping response received');
  }

  void publishMessage(String topic, String message) {
    final builder = MqttClientPayloadBuilder();
    builder.addString(message);
    client.publishMessage(topic, MqttQos.exactlyOnce, builder.payload!);
  }

  Stream<List<MqttReceivedMessage<MqttMessage>>>? getMessagesStream() {
    return client.updates;
  }
}

  Future<void> getInboxData() async {
    String? currentUserId = auth.currentUser?.uid;
    if (currentUserId != null) {
      try {
        // Listen to changes in the "Messages" collection where 'receiverId' is the current user ID
        firestore
            .collection("Messages")
            .where('receiverId', isEqualTo: currentUserId)
            .snapshots()
            .listen((querySnapshot) {
          List<String> differentUsersList = [];
          for (var doc in querySnapshot.docs) {
            var userInfo = doc.data();
            _urlImage = userInfo['imageUrl'];
            List<String> idsList = doc['idsList'];
            for (String id in idsList) {
              if (id == currentUserId) {
                return;
              }

              if (differentUsersList.contains(id)) {
                return;
              }
              differentUsersList.add(id);

              var inboxModel = InboxModel(
                name: '',
                message: doc['message'],
                image: '',
                backgroundColor: Colors.black,
                unReadMessages: 0,
                inboxId: '',
                uniqueId: doc['uniqueId'],
                receiverId: doc['receiverId'],
                senderId: doc['senderId'],
                timeStamp: doc['timeStamp'],
                idsList: doc['idsList'],
              );

              inboxModelList.add(inboxModel);
              // filter krna hai
            }

            // inboxModelList[].name = userInfo['name'] ?? inboxModelList[].name;
            // inboxModelList[].imageUrl = userInfo['imageUrl'] ?? inboxModelList[].imageUrl;
          }
          getOthersUserData(differentUsersList);

          // If the widget is still mounted, update the state
          if (mounted) {
            setState(() {});
          }
        });
      } catch (error) {
        print('Error fetching inbox data: $error');
      }
    } else {
      print('Error: Current user ID is null');
    }
  }

lib/main.dart
void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );
  runApp(MyApp());
}

import 'package:go_router/go_router.dart';

// GoRouter configuration
final _router = GoRouter(
  initialLocation: '/',
  routes: [
    GoRoute(
      name: 'home', // Optional, add name to your routes. Allows you navigate by name instead of path
      path: '/',
      builder: (context, state) => HomeScreen(),
    ),
    GoRoute(
      name: 'page2',
      path: '/page2',
      builder: (context, state) => Page2Screen(),
    ),
  ],
);

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      routerConfig: _router,
    );
  }
}

class NoteDatabase {
  static final NoteDatabase instance = NoteDatabase._internal();

  static Database? _database;

  NoteDatabase._internal();

  Future<Database> get database async {
    if (_database != null) {
      return _database!;
    }

    _database = await _initDatabase();
    return _database!;
  }

  Future<Database> _initDatabase() async {
    final databasePath = await getDatabasesPath();
    final path = '$databasePath/notes.db';
    return await openDatabase(
      path,
      version: 1,
      onCreate: _createDatabase,
    );
  }
}