Flutter Offline Sync

A Flutter package for offline data synchronization using both Hive and SQLite. This package ensures smooth data persistence and syncs with a remote server when the internet is available.

Features

• Dual Storage: Stores data using Hive (NoSQL) and SQLite (Relational DB).
• Automatic Sync: Data syncs with the server when online.
• Background Sync: Monitors connectivity changes for auto-sync.
• Optimized Read/Write: Uses the best available storage option.
• Custom Sync Implementation: Allows defining custom sync logic.
• Error Handling: Ensures safe data transactions.

Installation

Add the package dependencies to your pubspec.yaml:

dependencies:
  flutter:
    sdk: flutter
  connectivity_plus: ^5.0.2
  hive: ^2.2.3
  hive_flutter: ^1.1.0
  sqflite: ^2.3.0
  path_provider: ^2.1.2

Run:

flutter pub get

Usage

1. Initialize Sync Manager

In your main.dart, initialize the sync manager:

import 'package:flutter/material.dart';
import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:hive_flutter/hive_flutter.dart';
import 'sync_manager.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Hive.initFlutter();

  final syncManager = SyncManager();
  await syncManager.init();

  Connectivity().onConnectivityChanged.listen((event) {
    if (event != ConnectivityResult.none) {
      syncManager.syncData();
    }
  });

  runApp(MyApp());
}

2. Implement SyncManager

Create a SyncManager class to handle offline data storage and synchronization:

import 'package:hive/hive.dart';
import 'sqlite_db.dart';
import 'package:connectivity_plus/connectivity_plus.dart';

/// Manages offline data synchronization and local storage.
class SyncManager {
  late Box _box;

  /// Initializes Hive and SQLite databases.
  Future<void> init() async {
    _box = await Hive.openBox('offline_data');
    await SQLiteDB.init();
  }

  /// Saves data to both Hive and SQLite.
  Future<void> saveData(String key, dynamic value) async {
    _box.put(key, value);
    await SQLiteDB.insertData(key, value.toString());
  }

  /// Retrieves data from Hive first, then SQLite as fallback.
  Future<String?> getData(String key) async {
    return _box.get(key) ?? await SQLiteDB.getData(key);
  }

  /// Synchronizes offline data with the remote server when online.
  Future<void> syncData() async {
    if (await Connectivity().checkConnectivity() != ConnectivityResult.none) {
      var offlineData = _box.toMap();
      // Send data to the server
      print("Syncing data: \$offlineData");
      _box.clear();
      await SQLiteDB.clearDatabase();
    }
  }
}

3. SQLite Database Implementation

Create sqlite_db.dart to manage SQLite storage:

import 'package:sqflite/sqflite.dart';
import 'package:path/path.dart';

class SQLiteDB {
  static Database? _database;

  static Future<void> init() async {
    _database = await _initDB();
  }

  static Future<Database> _initDB() async {
    final path = join(await getDatabasesPath(), 'offline_data.db');
    return await openDatabase(
      path,
      version: 1,
      onCreate: (db, version) async {
        await db.execute('''
          CREATE TABLE offline_data (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            key TEXT UNIQUE,
            value TEXT
          )
        ''');
      },
    );
  }

  static Future<void> insertData(String key, String value) async {
    final db = await _database;
    await db?.insert('offline_data', {'key': key, 'value': value}, conflictAlgorithm: ConflictAlgorithm.replace);
  }

  static Future<String?> getData(String key) async {
    final db = await _database;
    final result = await db?.query('offline_data', where: 'key = ?', whereArgs: [key]);
    return result?.isNotEmpty == true ? result!.first['value'] as String : null;
  }

  static Future<void> clearDatabase() async {
    final db = await _database;
    await db?.delete('offline_data');
  }
}

4. Storing and Syncing Data

Save data locally and sync when online:

final syncManager = SyncManager();
await syncManager.saveData('user', {'name': 'John Doe', 'age': 25});

Retrieve stored data:

String? userData = await syncManager.getData('user');
print(userData);

Running Tests

To run tests, execute:

flutter test

Example Project

Check out the /example folder for a complete working example.

How to Run Example

1. Navigate to the example folder:

   cd example
   

2. Run the Flutter project:

   flutter run
   

Contributing

We welcome contributions! If you would like to contribute:

• Fork the repository.
• Create a new branch.
• Make your changes and submit a pull request.

For major changes, please open an issue first to discuss your proposal.

License

This project is licensed under the MIT License - see the LICENSE file for details.