rebloc 0.0.4

A state management library for Flutter that combines aspects of Redux and BLoC. Rebloc uses streams and BLoCs to compose middleware and reducers.

rebloc

A state management library for Flutter that combines aspects of Redux and BLoC (this readme assumes some familiarity with both). It's a personal project by redbrogdon, rather than an official library from the Flutter team.

What's going on here

Rebloc is an attempt to smoosh together two popular Flutter state management approaches: Redux and BLoC. It defines a Redux-y single direction data flow that involves actions, middleware, reducers, and a store. Rather than using functional programming techniques to compose reducers and middleware from parts and wire everything up, however, it uses BLoCs.

The store defines a dispatch stream that accepts new actions and produces state objects in response. In between, BLoCs are wired into the stream to function as middleware and reducers. The stream for a simple, two-BLoC store might look like this, for example:

Dispatch ->
  BloC #1 middleware ->
  BLoC #2 middleware ->
  the action becomes an accumulator (action and state together) ->
  BLoC #1 reducer ->
  BLoC #2 reducer ->
  resulting state object is emitted by store

There are two ways to implement BLoCs. The first is a basic Bloc<StateType> interface that allows direct access to the dispatch stream (meaning you can transform it, expand it, and do all sorts of other streamy goodness). The other is an abstract class, SimpleBloc<StateType>, that hides away interaction with the stream and provides a simple, functional interface.

Middleware methods can perform side effects like calling out to REST endpoints and dispatching new actions, but reducers should work as pure functions in keeping with Redux core principles. Middleware are also allowed to cancel actions.

Why does this exist?

State management is an open question for Flutter developers. I like the freedom of BLoCs, but the Redux pattern can offer things like easily composed reducers and middleware, great support for cross-cutting concerns like logging, and the potential for time-travel debugging if interest merits building those sorts of tools.

Thus I'd like to see if I can combine the two and get the parts I like from both. Also, it's a chance to test out...

ViewModelSubscriber

Also included in this library is a widget called ViewModelSubscriber. It looks for an InheritedWidget called StoreProvider above it to find a stream of app state objects to subscribe to. Then it converts each object that comes through the stream into a view model object and builds widgets with it. This is similar to a StreamBuilder, but with the benefit that a ViewModelSubscriber will ignore any state objects that don't cause a change to its view model.

What this means in practice is that if you're building a piece of UI that depends on one part of your overall app state, it will only be rebuilt and redrawn if that one particular bit of data changes. If you've got a list of complicated records, for example, you can use ViewModelSubscriber widgets to avoid rebuilding the entire list just because one field in one record changed.

Examples

Two examples are included (a basic one, and a list-based one) so you can see the library in action. It's also being used in the Voxxed Days conference app currently being built.

Feedback

I'm interested in whatever feedback other devs in the Flutter community may have, whether it's "This is awesome" or "This design is bad and you should feel bad." Feel free to file issues and feature requests, tweet at @RedBrogdon, and come join the conversation at the Flutter Dev Google group.