Bad state: Stream has already been listened to

[sgalway00]

I have successfully implemented your package but when I try to start the isolate a second time I get an error "Bad state: Stream has already been listened to." During the first activation everything works as expected.

static void callback(LocationDto locationDto) async {
    print('location in dart: ${locationDto.toString()}');

    final SendPort send = IsolateNameServer.lookupPortByName(_gpsIsolate);
    send?.send(locationDto);
  }

  void getLocationFromBackground(LocationDto inGpsData) async {
    print(inGpsData);
  }

  void startLocationService() {
    print('startLocationService started');
    BackgroundLocator.registerLocationUpdate(
      callback,
      //optional
      //androidNotificationCallback: notificationCallback,
      settings: LocationSettings(
          //Scroll down to see the different options
          notificationTitle: "Start Location Tracking example",
          notificationMsg: "Track location in background exapmle",
          wakeLockTime: 20,
          autoStop: false,
          interval: 1),
    );
  }

  void startGps2() async {
    print('startGps2 pressed');

    if (IsolateNameServer.lookupPortByName(_gpsIsolate) != null) {
      IsolateNameServer.removePortNameMapping(_gpsIsolate);
    }

     IsolateNameServer.registerPortWithName(
        gpsReceivePort.sendPort, _gpsIsolate);

     startLocationService();

    

     gpsReceivePort.listen((dynamic data) async {
      getLocationFromBackground(data);
      print('Incoming Data: $data');
    });
  }

  void stopGps2() async {
    BackgroundLocator.unRegisterLocationUpdate();
    IsolateNameServer.removePortNameMapping(_gpsIsolate);

    gpsReceivePort.close();

    print('stopGps2 pressed, Isolate stopped');

    
  }

VERBOSE-2:ui_dart_state.cc(157)] Unhandled Exception: Bad state: Stream has already been listened to. #0 _StreamController._subscribe (dart:async/stream_controller.dart:683:7) #1 _ControllerStream._createSubscription (dart:async/stream_controller.dart:833:19) #2 _StreamImpl.listen (dart:async/stream_impl.dart:475:9) #3 _ReceivePortImpl.listen (dart:isolate-patch/isolate_patch.dart:87:31) #4 GPSBloc.startGps2 package:yonav2/blocs/gpsBloc.dart:161 #5 _GpsSwitchState.build.<anonymous closure>.<anonymous closure> package:yonav2/gpsWidgets/gpsWidgets.dart:62 #6 _rootRunUnary (dart:async/zone.dart:1192:38) #7 _CustomZone.runUnary (dart:async/zone.dart:1085:19) #8 _FutureListener.handleValue (dart:async/future_impl.dart:141:18) #9 Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:682:45) #10 Future._propagateToListeners (dart:async/future_impl.dart:711:32) #11 Future._completeWithValue (dart:async/future_impl.da<…>

[leonardoayres]

Have you tried to close the Port and recreate it?

Move the:
gpsReceivePort.listen((dynamic data) async { getLocationFromBackground(data); print('Incoming Data: $data'); });

to a function and call it to recreate the Port.

[sgalway00]

From my code snippet above you can see that I do close the port in the stopGps2() function.

I don't understand what you mean my "move to a function". The listener should be in a separate function from where the port is created?

[leonardoayres]

@sgalway00 you could do something like that:

void _backgroundListener() {
if (gpsReceivePort != null) {
--- your code ---
} else {
--- create the port ---
}
}

But my scenario is that i'm only activate the background_locator when my app go to INACTIVE state, so i have to create and recreate the port in certains conditions.

[mehdok]

Closing this issue due inactivity, but feel free to open it anytime;