flutter getx web sockets - stream data to be cascaded to provider and controller-CodePudding

Objective is simple

flutter app makes a call to graphql api over websockets
app view calls the controller, controller calls the provider, provider calls the AWS appsync api over websockets or over HTTP api socket call
we receive a stream of data from appsync api or HTTP api socket call over websockets every now and then from backend
streams need to be cascaded back to provider , and then to controller (this is the critical step)
controller (not the provider) would update the obs or reactive variable, make the UI reflect the changes

problem : data is recieved via websockets in the caller, but never passed back as stream to provider or controller to reflect the changes

sample code

actual caller orderdata.dart

  @override
  Stream<dynamic> subscribe({
    String query,
    Map<String, dynamic> variables,
  }) async* {
    debugPrint('===->subscribe===');
    // it can be any stream here, http or file or image or media
    final Stream<GraphQLResponse<String>> operation = Amplify.API.subscribe(
      GraphQLRequest<String>(
        document: query,
        variables: variables,
      ),
      onEstablished: () {
        debugPrint(
          '===->subscribe onEstablished ===',
        );
      },
    );

    operation.listen(
      (event) async* {
        final jsonData = json.decode(event.data.toString());
        debugPrint('===->subscription data $jsonData');
        yield jsonData;
      },
      one rror: (Object e) => debugPrint('Error in subscription stream: $e'),
    );
  }

in the provider orderprovider.dart

  Stream<Order> orderSubscription(String placeId) async* {
    debugPrint('===->=== $placeId');
    subscriptionResponseStream = orderData.subscribe(
      query: subscribeToMenuOrder,
      variables: {"place_id": placeId},
    );

    subscriptionResponseStream.listen((event) async* {
      debugPrint(
        "===->=== yielded $event",
      );
      yield event;
    });
    debugPrint('===->=== finished');
  }

in the controller homecontroller.dart

  Future<void> getSubscriptionData(String placeId) async {
    debugPrint('===HomeController->getSubscriptionData===');
    OrderProvider().orderSubscription(placeId).listen(
          (data) {
            //this block is executed when data event is receivedby listener
            debugPrint('Data: $data');
            Get.snackbar('orderSubscription', data.toString());
          },
          one rror: (err) {
            //this block is executed when error event is received by listener
            debugPrint('Error: $err');
          },
          cancelOnError:
              false, //this decides if subscription is cancelled on error or not
          onDone: () {
            //this block is executed when done event is received by listener
            debugPrint('Done!');
          },
        );
  }

homeview calls homecontroller

CodePudding user response：

Try using map for transforming Streams:

 @override
  Stream<dynamic> subscribe({
    String query,
    Map<String, dynamic> variables,
  }) {
    debugPrint('===->subscribe===');
    // it can be any stream here, http or file or image or media
    final Stream<GraphQLResponse<String>> operation = Amplify.API.subscribe(
      GraphQLRequest<String>(
        document: query,
        variables: variables,
      ),
      onEstablished: () {
        debugPrint(
          '===->subscribe onEstablished ===',
        );
      },
    );
    
    return operation.map((event) {
      return json.decode(event.data);
    });
  }

  // elsewhere

  final subscription = subscribe(
    query: 'some query', 
    variables: {},
  );

  subscription.listen(
    (jsonData) {
      debugPrint('===->subscription data $jsonData');
    },
    one rror: (Object e) => debugPrint('Error in subscription stream: $e'),
  );