Bloc: Using streams in mapEventToState

[algirdasmac]

Hello,

I have a question regarding the best approach for working with streams in BLoC. Below is one specific use case, but I was wondering about similar approaches in other use cases.

What I am trying to do:

1. When user clicks a button with one of his addresses on screen, I want to dispatch an event SelectAddress.
2. In BLoC I want to map this event with State. I am receiving Address object (latitude, longitude and etc.) with an SelectAddress event, pass it to GeoFlutterFire library method and get Stream<List<Store>>.
3. After receiving data, I want to update State with new values from List<Store>.
4. After State changes, I change view (showing user locations nearby).

Where I am stuck
First part works, second and third does not. Last part is OK.

I have a repository, which returns Stream<List<Store>> from Firestore (plugin is https://pub.dartlang.org/packages/geoflutterfire), but this stream emits at least 8-9 events, before it returns list with documents.
I am trying to listen to this stream in mapEventToState, but StreamSubscription does not work at all:

    if (event is SelectAddress) {
      yield state.copyWith(isLoading: true);
      try {
        StreamSubscription streamSubscription;
        Stream<List<Store>> _storeListStream =
            _databaseInterface.getNearbyStores(event.deliveryAddress, 5);
        streamSubscription = _storeListStream.listen((stores) async* {
          if (stores.isNotEmpty) {
            yield state.copyWith(
              isLoading: false,
              deliveryAddress: event.deliveryAddress,
              isAddressSelected: true,
              listOfStores: stores,
            );
          } else {
            yield state.copyWith(isLoading: false);
          }
        });
      } catch (error) {
        yield state.copyWith(isLoading: false, error: error);
      }
    }

When using await for method, I cannot pass new events to this bloc after SelectAddress event:

    if (event is SelectAddress) {
      yield state.copyWith(isLoading: true);
      try {
        Stream<List<Store>> _storeListStream =
            _databaseInterface.getNearbyStores(event.deliveryAddress, 5);
        await for (List<Store> stores in _storeListStream) {
          if (stores.isNotEmpty)
            yield state.copyWith(
              isLoading: false,
              deliveryAddress: event.deliveryAddress,
              isAddressSelected: true,
              listOfStores: stores,
            );
        }
      } catch (error) {
        yield state.copyWith(isLoading: false, error: error);
      }
    }

I have a feeling I am not using the right approach.
Any help would be appreciated.

[felangel]

Hi @algirdasmac thanks for opening an issue!

Right off the bat, I wouldn't recommend creating a subscription directly in mapEventToState because mapEventToState gets called every time an event is dispatched. I would instead move all of the logic for getting nearby stores into a StoreRepository and just expose a public getNearbyStores which returns a Future of nearby stores. Then in mapEventToState you can do something like:

if (event is SelectAddress) {
      yield state.copyWith(isLoading: true);
      try {
        List<Store> stores =
            await _storeRepository.getNearbyStores(event.deliveryAddress, 5);
        yield state.copyWith(
              isLoading: false,
              deliveryAddress: event.deliveryAddress,
              isAddressSelected: true,
              listOfStores: stores,
            );
      } catch (error) {
        yield state.copyWith(isLoading: false, error: error);
      }
}

If this answer doesn't make sense then:

• Are you able to give me read-only access to the repo?
  
  
  
  • If so, I can take a look and potentially open a PR to fix the issue.
  
  
  • If not, it'd be really helpful if you could create a simple app that demonstrates the problem you're having.
  
  

Let me know if that helps! 👍

[algirdasmac]

Thanks @felangel - you are always as fast as it can be - impressive!
Although this answer makes sense, it's just not what I am looking for. Unfortunately I can't give access to the repo (company policy), but I created simple flutter app with the situation:
https://github.com/algirdasmac/streams_and_blocs

In /lib/todo_bloc/todo_bloc.dart I try to take stream results and add them to state. What I would try to do later is to listen to Firestore collection and show todo's to user (in case other user added some todo's).

I hope this is clear. If it is not - please do not hesitate to ask and I will try to explain even more. Thanks.

PS. I am looking more of an advice here, it should not be considered as an issue.

[felangel]

@algirdasmac no problem haha! I'll take a look shortly and will try to open a PR with some suggestion. 👍

[felangel]

@algirdasmac just opened a PR to connect the bloc to Firestore. Let me know if that helps!

Marking this as closed since it's more of a discussion at this point 😄

[algirdasmac]

So simple and so effective. It is strange to me that I didn't think about it myself. Thanks @felangel !

[fvisticot]

I had exactly the same pb and this PR help me.
Question: This sample is using the previous State management implementation without "Equatable".

How easy it is to use the new Equatable solution to manage the state variables (todos) ?
Can you please update the sample ?

I have some difficulties to manage the different class to easily manage the variable (todos)

[felangel]

@fvisticot what sample are you referring to? Examples/flutter_todos?

[fvisticot]

I'm referring to https://github.com/algirdasmac/streams_and_blocs
I try to do the "same" thing with Firebase / Stream integration inside a bloc.
Would like to find a simple solution to manage Firebase data from Stream and Bloc/State

My "pb" is to manage the data (List) between the different state classes

[fvisticot]

It's OK with todo sample code. Tx for your help.

[felangel]

@fvisticot Just want to confirm, you were able to solve your issue?

[fvisticot]

Yep, My issue is solved.
I'm using your solution with Todo sample.
My only "pb" was your solution to manage the updatedTodos
You only update this list in the state TodosLoaded
I was not sure if "else" cases can occurs