Applications often need to sync data when they’re not in active use. This document explains background syncing implementations with PowerSync.

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Platform Support

Background syncing has been tested in: These examples can be adapted for other frameworks like React Native. For implementation questions or assistance, chat to us on Discord.

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Flutter Implementation Guide

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Prerequisites

  1. Complete the workmanager platform setup
  2. Review the Supabase To-Do List Demo for context

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Configure the Background Task

In main.dart: 
void main() async {
  // ... existing setup code ...
  
  const simpleTaskKey = "com.domain.myapp.taskId";
  
  // Mandatory if the App is obfuscated or using Flutter 3.1+
  @pragma('vm:entry-point')
  void callbackDispatcher() {
    Workmanager().executeTask((task, inputData) async {
      switch (task) {
        case simpleTaskKey:
          // Initialize PowerSync database and connection
          final currentConnector = await openDatabase();
          db.connect(connector: currentConnector!);
          
          // Perform database operations
          await TodoList.create('New background task item');
          await currentConnector.uploadData(db);
          await TodoList.create('testing1111');
          await currentConnector.uploadData(db);
          // print("$simpleTaskKey was executed. inputData = $inputData");
          break;
      }
      // Close database when done
      await db.close();
      return Future.value(true);
    });
  }

  // Initialize the workmanager with your callback
  Workmanager().initialize(
    callbackDispatcher,
    // Shows notifications during task execution (useful for debugging)
    isInDebugMode: true
  );
  
  // ... rest of your app initialization ...
}
Note specifically in the switch statement: 
// currentConnector is the connector to the remote DB
// openDatabase sets the db variable to the PowerSync database
final currentConnector = await openDatabase();
// connect PowerSync to the remote database
db.connect(connector: currentConnector!);
// a database write operation
await TodoList.create('Buy new shoes');
// Sync with the remote database
await currentConnector.uploadData(db);
  1. Since WorkManager executes in a new process, you need to set up the PowerSync local database and connect to the remote database using your connector.
  2. Run a write (in the case of this demo app, we create a ‘todo list’)
  3. Make sure to run currentConnector.uploadData(db); so that the local write is uploaded to the remote database.

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Testing

Add a test button: 
  ElevatedButton(
  title: const Text("Start the Flutter background service"),
     onTap: () async {
        await Workmanager().cancelAll();
        // print("RUN BACKGROUND TASK");
        await Workmanager().registerOneOffTask(
        simpleTaskKey,
        simpleTaskKey,
        initialDelay: Duration(seconds: 10),
        inputData: <String, dynamic>{
        int': 1,
      },
    );
  },
),
Press the button, background the app, wait 10 seconds, then verify new records in the remote database.

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Platform Compatibility

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Android

  • Implementation works as expected.

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iOS

  • At the time of last testing this (January 2024), we were only able to get part of this to work using the branch for this PR into workmanager.
  • While testing we were not able to get iOS background fetching to work, however this is most likely an issue with the package.