Pass parameters to the callback function

[darshansatra1]

Future<void> startPeriodicTask({
  required int steps,
  required int yesterdaySteps,
}) async {
  await FlutterForegroundTask.start(
      notificationTitle: "Notification", 
      callback: periodicTaskFun,
);
}

Right now I'm using this code to register the callback function, but can I pass parameters like String or Int to periodicTaskFun? If not please can you add such a feature?

[Dev-hwang]

Since the periodicTaskFun function is a top-level function, parameters cannot be passed directly. Use a mobile database like sqlite.

This is an example using sqflite. #9 (comment)

[darshansatra1]

Can you please go through this Object Box Issue. I have been trying to get the same instance of Store but as I'm making an instance from 2 different isolates the HashCodes are not the same because of which I'm not able to access the same store.

[Dev-hwang]

I've checked the requirements, but there doesn't seem to be a way right now. I'll keep thinking about how to pass a SendPort or parameters.

[darshansatra1]

Yes, it would be of great help if we can send some parameters in the callback function or can communicate with the main isolate.

[darshansatra1]

Future<void> startPeriodicTask({
  required int steps,
  required int yesterdaySteps,
  required Store store,
}) async {
  var port = ReceivePort();
  IsolateNameServer.registerPortWithName(port.sendPort, mainIsolatePortName);
  await FlutterForegroundTask.start(
    notificationTitle: "Today: $steps steps",
    notificationText: 'Yesterday: $yesterdaySteps steps',
    callback: periodicTaskFun,
  );
  final taskPort = (await port.first) as SendPort;
  taskPort.send(store.reference);
  IsolateNameServer.removePortNameMapping(mainIsolatePortName);
}


void periodicTaskFun() async {
  Stream<StepCount> _stepCountStream = Pedometer.stepCountStream;
  StreamSubscription<StepCount>? streamSubscription;
  final port = ReceivePort();
  IsolateNameServer.lookupPortByName(mainIsolatePortName)!.send(port.sendPort);
  final storeRef = (await port.first) as ByteData;
  LocalDataSource localDataSource = LocalDataSourceImpl();
  await localDataSource.initializeForForegroundService(reference: storeRef);
  FlutterForegroundTask.initDispatcher((timeStamp) async {
    if (streamSubscription != null) {
      return;
    }...

So this was the solution I got from Internet and it's working now. But when I kill the app and reopen it, It's throwing me an error.

Error:

 Tried to send a platform message to Flutter, but FlutterJNI was detached from native C++. Could not send. Channel: step_count. Response ID: 0

Do you have any idea why this is happening?

[Dev-hwang]

The above problem occurs if the cancel function of streamSubscription is not called. If the problem persists despite writing the code, check if the onDestroy in the initDispatcher function is working properly.

[darshansatra1]

So I checked the onDestroy function and it is working. But this error actually occurs when in the following steps:

1. I run the foreground service.
2. I kill the app.
3. And I walk to see whether the stream is updating or not.
4. It is updating but at the same time, it is throwing me the error.

Is this supposed to happen?

[Dev-hwang]

objectbox/objectbox-dart@e61ea42

I tested with the above file and there was no problem.
It may be a BroadcastStream problem, so can you try adding onCancel as below?

final _stepCountStream =
    Stream<StepCount?>.periodic(const Duration(seconds: 10))
        .asBroadcastStream(onCancel: (subscription) => subscription.cancel());

[darshansatra1]

I tried this but nothing changed. I think there is some issue with flutter.