Flutter Workmanager
PR #647

Debugging Background Tasks

Debug and troubleshoot background tasks on Android and iOS

Background tasks can be tricky to debug since they run when your app is closed. Here's how to effectively debug and troubleshoot them on both platforms.

Hook-Based Debug System

The Workmanager plugin uses a hook-based debug system that allows you to customize how debug information is handled.

Quick Setup

Initialize Workmanager without any debug parameters:

dart
await Workmanager().initialize(callbackDispatcher);

Then set up platform-specific debug handlers as needed.

Android Debug Handlers

Logging Debug Handler (Recommended)

Shows debug information in Android's Log system (visible in adb logcat):

kotlin
// In your Application class
import dev.fluttercommunity.workmanager.WorkmanagerDebug
import dev.fluttercommunity.workmanager.LoggingDebugHandler

class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        WorkmanagerDebug.setCurrent(LoggingDebugHandler())
    }
}

Notification Debug Handler

Shows debug information as notifications (requires notification permissions):

kotlin
import dev.fluttercommunity.workmanager.NotificationDebugHandler

class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        WorkmanagerDebug.setCurrent(NotificationDebugHandler())
    }
}

iOS Debug Handlers

Logging Debug Handler (Recommended)

Shows debug information in iOS's unified logging system:

swift
// In your AppDelegate.swift
import workmanager_apple

@main
class AppDelegate: FlutterAppDelegate {
    override func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
    ) -> Bool {
        WorkmanagerDebug.setCurrent(LoggingDebugHandler())
        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }
}

Notification Debug Handler

Shows debug information as notifications:

swift
WorkmanagerDebug.setCurrent(NotificationDebugHandler())

Custom Debug Handlers

Create your own debug handler for custom logging needs:

kotlin
class CustomDebugHandler : WorkmanagerDebug() {
    override fun onTaskStatusUpdate(context: Context, taskInfo: TaskDebugInfo, status: TaskStatus, result: TaskResult?) {
        // Custom status handling logic
        // See Task Status documentation for detailed status information
    }
    
    override fun onExceptionEncountered(context: Context, taskInfo: TaskDebugInfo?, exception: Throwable) {
        // Handle exceptions
    }
}

WorkmanagerDebug.setCurrent(CustomDebugHandler())

For detailed information about task statuses, lifecycle, and notification formats, see the Task Status Tracking guide.

Android Debugging

Job Scheduler Inspection

Use ADB to inspect Android's job scheduler:

bash
# View scheduled jobs
adb shell dumpsys jobscheduler | grep yourapp

# View detailed job info  
adb shell dumpsys jobscheduler yourapp

# Force run job (debug only)
adb shell cmd jobscheduler run -f yourapp JOB_ID

Monitor Job Execution

bash
# Monitor WorkManager logs
adb logcat | grep WorkManager

# Monitor app background execution
adb logcat | grep "yourapp"

Common Android Issues

Tasks not running:

  • Check battery optimization settings
  • Verify app is not in "App Standby" mode
  • Ensure device isn't in Doze mode
  • Check if constraints are too restrictive

Tasks running too often:

  • Android enforces minimum 15-minute intervals for periodic tasks
  • Use appropriate constraints to limit execution

Debug Commands

bash
# Check if your app is whitelisted from battery optimization
adb shell dumpsys deviceidle whitelist

# Check battery optimization status
adb shell settings get global battery_saver_constants

# Force device into idle mode (testing)
adb shell dumpsys deviceidle force-idle

iOS Debugging

Console Logging

iOS background tasks have limited execution time. Add detailed logging:

dart
@pragma('vm:entry-point')
void callbackDispatcher() {
  Workmanager().executeTask((task, inputData) async {
    print('[iOS BG] Task started: $task at ${DateTime.now()}');
    
    try {
      // Your task logic
      final result = await performTask();
      print('[iOS BG] Task completed successfully');
      return true;
    } catch (e) {
      print('[iOS BG] Task failed: $e');
      return false;
    }
  });
}

Xcode Debugging

For Background Fetch tasks: Use Debug → Perform Fetch from the Xcode run menu while your app is running.

For BGTaskScheduler tasks (processing/periodic): Use Xcode's console to trigger tasks manually:

objc
// Trigger specific BGTaskScheduler task
e -l objc -- (void)[[BGTaskScheduler sharedScheduler] 
  _simulateLaunchForTaskWithIdentifier:@"com.yourapp.task.identifier"]

Monitor Scheduled Tasks

Check what tasks iOS has scheduled:

dart
// iOS 13+ only
if (Platform.isIOS) {
  final tasks = await Workmanager().printScheduledTasks();
  print('Scheduled tasks: $tasks');
}

This prints output like:

text
[BGTaskScheduler] Task Identifier: your.task.id earliestBeginDate: 2023.10.10 PM 11:10:12
[BGTaskScheduler] There are no scheduled tasks

Common iOS Issues

Background App Refresh disabled:

Tasks never run:

Tasks stop working:

Tasks run but don't complete:

General Debugging Tips

Add Comprehensive Logging

dart
@pragma('vm:entry-point')
void callbackDispatcher() {
  Workmanager().executeTask((task, inputData) async {
    final startTime = DateTime.now();
    print('🚀 Task started: $task');
    print('📊 Input data: $inputData');
    
    try {
      // Your task implementation
      final result = await performTask(task, inputData);
      
      final duration = DateTime.now().difference(startTime);
      print('✅ Task completed in ${duration.inSeconds}s');
      
      return result;
    } catch (e, stackTrace) {
      final duration = DateTime.now().difference(startTime);
      print('❌ Task failed after ${duration.inSeconds}s: $e');
      print('📋 Stack trace: $stackTrace');
      
      return false; // Retry
    }
  });
}

Test Task Logic Separately

Create a way to test your background logic from the UI:

dart
// Add a debug button to test task logic
ElevatedButton(
  onPressed: () async {
    // Test the same logic that runs in background
    final result = await performTask('test_task', {'debug': true});
    print('Test result: $result');
  },
  child: Text('Test Task Logic'),
)

Monitor Task Health

Track when tasks last ran successfully:

dart
Future<void> saveTaskExecutionTime(String taskName) async {
  final prefs = await SharedPreferences.getInstance();
  await prefs.setString('${taskName}_last_run', DateTime.now().toIso8601String());
}

Future<bool> isTaskHealthy(String taskName, Duration maxAge) async {
  final prefs = await SharedPreferences.getInstance();
  final lastRunString = prefs.getString('${taskName}_last_run');
  
  if (lastRunString == null) return false;
  
  final lastRun = DateTime.parse(lastRunString);
  final age = DateTime.now().difference(lastRun);
  
  return age &lt; maxAge;
}

Platform-Specific Testing

Android Testing Workflow

  1. Enable debug mode and install app
  2. Schedule task and verify it appears in job scheduler
  3. Put device to sleep and wait for execution
  4. Check debug notifications to confirm execution
  5. Use ADB commands to force execution if needed

iOS Testing Workflow

  1. Test on physical device (simulator doesn't support background tasks)
  2. Enable Background App Refresh in iOS Settings
  3. Use Xcode debugger to trigger tasks immediately
  4. Monitor Xcode console for logging output
  5. Check iOS Settings > Battery for background activity

Troubleshooting Checklist

Quick Checks:

  • Workmanager initialized in main()
  • Task names are unique
  • Platform setup completed (iOS setup guide)
  • Debug handler configured (see Debug Handlers)

Performance & Reliability:

  • Task logic optimized for background execution
  • Dependencies initialized in background isolate
  • Error handling with try-catch blocks
  • iOS 30-second execution limit respected

Remember: Background task execution is controlled by the operating system and is never guaranteed. Always design your app to work gracefully when background tasks don't run as expected.

Task Status Tracking

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