In my Flutter app I fetch about 20,000 items from my Supabase backend and then save it my local storage using Floor. Fetching is fast but looping through is what takes a lot of time and its bad on UX.

@override
  Future<void> saveProfiles(List<Profile> profiles) async {
    try {
      logger('${profiles.length} profiles to be saved');
      if (profiles.isNotEmpty) {
        for (final profile in profiles) {
          await _database.profilesDao.insertProfile(profile);
        }
      }
    } catch (e) {
      logger('Unable to save profiles: $e');
    }
  }

My app is supposed to profile offline access because the target market are in the rural areas otherwise I would not be going through all this pain to do this. So I tried to set up workmanager like this in my bloc

class ProfilesSaveBloc extends Bloc<ProfilesSaveEvent, ProfilesSaveState> {
  ProfilesSaveBloc() : super(const _ProfilesSaveState()) {
    on<SaveProfiles>(_onSaveProfiles);
  }

  void _onSaveProfiles(
    SaveProfles event,
    Emitter<ProfilesSaveState> emit,
  ) async {
    emit(const ProfilesLoadingState());
    
    Workmanager().registerOneOffTask(
      'saveProfilesTask',
      'saveProfilesTask',
      inputData: {
        'profiles': event.profiles.map((profile) => profile.toJson()).toList(),
      },
    );

    emit(const ProfilesSavedState());
  }
}

Now in my main.dart I did do my stuff there too

@pragma('vm:entry-point')
void callbackDispatcher() {
  Workmanager().executeTask((task, inputData) async {
    try {
      await configureDependencies(Environments.production);
      switch (task) {
        case 'saveProfilesTask':
          final List<dynamic> rawData = inputData!['profiles'];
          final profiles = rawData.map((json) => Profle.fromJson(json)).toList();
          final dbRepo = getIt<DatabaseRepository>();
          await dbRepo.saveProfiles(profiles);
          break;
      }
    } catch (e) {
      logger('Callback failed: $e');
    }
    return Future.value(true);
  });
}

Future<void> main() async {
  logger('Starting app from main.dart');
  WidgetsFlutterBinding.ensureInitialized();
  await configureDependencies(Environments.production);

  Workmanager().initialize(callbackDispatcher, isInDebugMode: false);

  runApp(const MyApp());
}

My dependency injection which uses code generation thanks to get_it looks like this

final getIt = GetIt.instance;

@InjectableInit(
  initializerName: r'initGetIt',
  generateForDir: ['lib'],
)
Future<void> configureDependencies(String environment) async {
  logger('Using environment: $environment');
  await getIt.initGetIt(environment: environment);
  await getIt.allReady();
}

@module
abstract class RegisterModule {
  @singleton
  @preResolve
  Future<SharedPreferences> prefRepo() => SharedPreferences.getInstance();

  @singleton
  @preResolve
  Future<AppDatabase> provideAppDatabase() async => await $FloorAppDatabase
      .databaseBuilder(await AppConstants.databaseFile)
      .build();

  @lazySingleton
  DatabaseRepository provideDatabaseRepository(AppDatabase appDatabase) =>
      DatabaseRepositoryImpl(appDatabase);
}

dynamic _parseAndDecode(String response) => jsonDecode(response);

dynamic parseJson(String text) =>
    compute<String, dynamic>(_parseAndDecode, text);

I am sure I followed all the guidelines including the android manifest

    android:enableOnBackInvokedCallback="true"

But my workmanager doesn't fire up and do what I need it to do. I am frustrated