Flutter Location Tracking in the Background: Handling App Termination

This article details how to implement background location tracking in a Flutter application, specifically addressing the issue of app termination and ensuring continuous location updates every 30 seconds. It outlines the best practices and possible error handling scenarios.

The Problem: App Termination and Background Location Updates

Many Flutter applications require continuous location tracking, even when the application is in the background or terminated by the user. The built-in Flutter location services are designed for foreground access. Using standard methods, data isn’t reliably collected if the application is closed.

The Solution: Using Background Services and Isolates

To achieve continuous location updates even when the app is in the background or terminated, consider these techniques:

1. Background Service with Isolates

Combine a background service with an isolate to handle the continuous location retrieval. The isolate ensures that location updates continue uninterrupted even after the main application thread is terminated.

import 'dart:async';
import 'package:flutter_background_service/flutter_background_service.dart';
import 'package:geolocator/geolocator.dart';
import 'package:flutter/foundation.dart';

// ... other imports

class LocationService extends BackgroundService {
  @override
  Future onStart(ServiceInstance service) async {
    // Set isRunning to true to allow the isolate to run
    service.on('start', (event) {
      // start background task
    });

    // Start the location update loop in a separate isolate
    _locationUpdatesIsolate();
  }
  
  @override
  Future onStop(ServiceInstance service) async {
    // Stop the location update loop
    // ...
  }

  Future _locationUpdatesIsolate() async {
    // Start location service in isolate, preventing main thread block
    Isolate.spawn(_updateLocation, null);
  }

  static Future _updateLocation(dynamic data) async {
    // Initialize location service
    // ...

    while(isRunning){ // Condition to allow isolate loop
      try {
        LocationPermission permission = await Geolocator.requestPermission();
        if (permission == LocationPermission.denied) {
            // Handle permission denial.
          return;
        }

        Position position = await Geolocator.getCurrentPosition();
        // ... Send data ...
        print(position.toString()); // Example print statement
      } catch (e) {
        print("Error updating location: $e");
      }
      await Future.delayed(const Duration(seconds: 30)); // update every 30 seconds
    }
  }


}
// ... other parts of the class

2. Error Handling

Implement comprehensive error handling within the isolate’s _updateLocation function:

• Location Permissions: Check for location permissions regularly. If permission is denied, handle it gracefully. Guide the user to enable permissions.
• Geolocator Errors: Catch any exceptions from the Geolocator library (e.g., location unavailable, permission issues). Provide informative error messages to the user and log errors appropriately.
• Network Errors: Consider network errors if you’re sending location data. Implement retry mechanisms or alternative data storage.
• Isolate Communication: Ensure communication with the main thread if needed for updating UI components or performing UI interactions.

3. Important Considerations:

• Background Services Package: Use a suitable background service package (e.g., flutter_background_service) to handle the background service. Ensure compatibility with your Flutter version.
• Platform Differences: Background services and access to locations behave differently between Android and iOS. Consider platform-specific limitations.
• Battery Usage: Be mindful of battery consumption, especially for continuous location tracking in the background. Consider optimizing the frequency and duration of location updates.

Possible Errors and Solutions

By combining background services and isolates, you can implement robust location tracking, ensuring data collection in Flutter even when the application is terminated.