OfflineSync

OfflineSync is a Flutter package that provides offline-first data management and synchronization. It ensures smooth functionality even without an internet connection and syncs data once connectivity is restored.

Features

  • Local data storage and retrieval
  • Automatic synchronization with server when online
  • Conflict resolution
  • Encryption of sensitive data
  • Batch syncing for improved performance
  • Error handling and retry mechanisms

Installation

Add this to your package's pubspec.yaml file:

dependencies:
  offline_sync: ^1.0.0

Usage

Initialization

First, initialize the OfflineSync instance in your app:

import 'package:offline_sync/offline_sync.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final offlineSync = OfflineSync(
    config: OfflineSyncConfig(
      apiEndpoint: 'https://your-custom-api.com',
      // encryptionKey is optional and will be generated automatically if not provided
    ),
  );
  await offlineSync.initialize();
  runApp(MyApp());
}

Setting Custom API Endpoint

Set a custom endpoint for your specific server:

final offlineSync = OfflineSync();
offlineSync.setApiEndpoint('https://your-custom-api.com');

Saving Data

To save data locally and queue it for syncing:

final offlineSync = OfflineSync();
await offlineSync.saveLocalData('user_1', {
  'name': 'John Doe',
  'email': 'john@example.com',
  'age': 30,
});

Reading Data

To read locally stored data:

final userData = await offlineSync.readLocalData('user_1');
if (userData != null) {
  print('User name: ${userData['name']}');
} else {
  print('User not found');
}

Syncing with Server

The package automatically syncs data when an internet connection is available. However, you can manually trigger a sync:

try {
  await offlineSync.updateFromServer();
  print('Data updated from server successfully');
} catch (e) {
  print('Failed to update from server: $e');
}

Handling Authentication

Set the authentication token for API requests:

await offlineSync.setAuthToken('your_auth_token_here');

Advanced Usage:

Conflict Resolution

The package includes basic conflict resolution. You can customize this by extending the OfflineSync class:

class CustomOfflineSync extends OfflineSync {
  @override
  Future<Map<String, dynamic>> resolveConflict(
    String id,
    Map<String, dynamic> localData,
    Map<String, dynamic> serverData
  ) async {
    // Implement your custom conflict resolution strategy here
    // This example prefers local changes
    final resolvedData = Map<String, dynamic>.from(serverData);
    localData.forEach((key, value) {
      if (value != serverData[key]) {
        resolvedData[key] = value;
      }
    });
    return resolvedData;
  }
}

Batch Processing

The package processes sync queue in batches. You can adjust the batch size:

class CustomOfflineSync extends OfflineSync {
  @override
  int get batchSize => 100; // Default is 50
}

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

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

Using with Flutter Provider

Wrap your app with the OfflineSyncProvider to make the sync instance and its status available throughout the widget tree:

final offlineSync = OfflineSync(config: OfflineSyncConfig(
  apiEndpoint: 'https://your-api.com',
  // encryptionKey is now optional
));
await offlineSync.initialize();

runApp(
  OfflineSyncProvider(
    offlineSync: offlineSync,
    child: MyApp(),
  ),
);

Then, anywhere in your widget tree, you can access the sync instance and status:

final offlineSync = OfflineSyncProvider.of(context);
ValueListenableBuilder<SyncStatus>(
  valueListenable: offlineSync.syncStatus,
  builder: (context, status, _) {
    // Show sync status in UI
    return Text('Sync status: $status');
  },
)

API Reference

OfflineSyncConfig

  • apiEndpoint (String, required): The server endpoint for syncing.
  • batchSize (int, default: 50): Number of items to sync per batch.
  • encryptionKey (String, optional): 32-character key for AES encryption. If not provided, a secure key is generated and stored automatically.
  • encryptionIV (IV, optional): Custom IV for encryption.
  • conflictResolver (callback, optional): Custom function for resolving data conflicts.
  • logger (callback, optional): Function for debug or error logging.

OfflineSync

  • OfflineSync({required OfflineSyncConfig config, ...}): Create a new instance with config and optional injected dependencies.
  • Future<void> initialize(): Initialize the database and connectivity.
  • Future<void> setAuthToken(String token): Set the auth token for API requests.
  • Future<void> saveLocalData(String id, Map<String, dynamic> data): Save data locally and queue for sync.
  • Future<Map<String, dynamic>?> readLocalData(String id): Read local data by ID.
  • Future<void> updateFromServer(): Manually trigger sync from server.
  • ValueNotifier<SyncStatus> syncStatus: Listen for sync status changes.
  • ValueNotifier<SyncErrorType?> lastError: Listen for error changes.
  • ValueNotifier<double> syncProgress: Listen for sync progress (0.0 to 1.0).

Migration Guide

From Singleton to Instance API

  • Before: 
    final offlineSync = OfflineSync();
await offlineSync.initialize();
offlineSync.setApiEndpoint('https://api.com');
  • After: 
    final offlineSync = OfflineSync(
  config: OfflineSyncConfig(
    apiEndpoint: 'https://api.com',
    // encryptionKey is now optional
  ),
);
await offlineSync.initialize();
  • Use the new OfflineSyncProvider to expose the instance to your widget tree.
  • Set all configuration options via OfflineSyncConfig instead of setters.

Libraries

offline_sync