flutter_flux

The latest version of flutter_flux can be found at https://github.com/flutter/flutter_flux

A Dart app architecture library with uni-directional data flow inspired by RefluxJS and Facebook's Flux.

• Overview
• What's Included
  • Action
  • Store
  • FluxComponent
• Examples
• External Consumption

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Overview

flutter_flux implements a uni-directional data flow pattern comprised of Actions, Stores, and StoreWatchers. It is based on w_flux, but modified to use Flutter instead of React.

• Actions initiate mutation of app data that resides in Stores.
• Data mutations within Stores trigger re-rendering of app view (defined in StoreWatcher).
• Flutter Widgets and other interaction sources dispatch Actions in response to user interaction.
• and the cycle continues...

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What's Included

Action

An Action is a command that can be dispatched (with an optional data payload) and listened to.

In flutter_flux, Actions are the sole driver of application state change. Widgets and other objects dispatch Actions in response to user interaction with the rendered view. Stores listen for these Action dispatches and mutate their internal data in response, taking the Action payload into account as appropriate.

import 'package:flutter_flux/flutter_flux.dart';

// define an action
final Action<String> displayString = new Action<String>();

// dispatch the action with a payload
displayString('somePayload');

// listen for action dispatches
displayString.listen(_displayAlert);

_displayAlert(String payload) {
  print(payload);
}

BONUS: Actions are await-able!

They return a Future that completes after all registered Action listeners complete. It's NOT generally recommended to use this feature within normal app code, but it is quite useful in unit test code.

Store

A Store is a repository and manager of app state. The base Store class provided by flutter_flux should be extended to fit the needs of your app and its data. App state may be spread across many independent stores depending on the complexity of the app and your desired app architecture.

By convention, a Store's internal data cannot be mutated directly. Instead, Store data is mutated internally in response to Action dispatches. Stores should otherwise be considered read-only, publicly exposing relevant data ONLY via getter methods. This limited data access ensures that the integrity of the uni-directional data flow is maintained.

A Store can be listened to to receive external notification of its data mutations. Whenever the data within a Store is mutated, the trigger method is used to notify any registered listeners that updated data is available. In flutter_flux, StoreWatchers listen to Stores, typically triggering re-rendering of UI elements based on the updated Store data.

import 'package:flutter_flux/flutter_flux.dart';

class RandomColorStore extends Store {

  // Public data is only available via getter method
  String _backgroundColor = 'gray';
  String get backgroundColor => _backgroundColor;

  // Actions relevant to the store are passed in during instantiation
  RandomColorActions _actions;

  RandomColorStore(RandomColorActions this._actions) {
    // listen for relevant action dispatches
    _actions.changeBackgroundColor.listen(_changeBackgroundColor);
  }

  _changeBackgroundColor(_) {
    // action dispatches trigger internal data mutations
    _backgroundColor = '#' + (new Random().nextDouble() * 16777215).floor().toRadixString(16);

    // trigger to notify external listeners that new data is available
    trigger();
  }
}

BONUS: Stores can be initialized with a stream transformer to modify the standard behavior of the trigger stream. This can be useful for throttling UI rendering in response to high frequency Store mutations.

import 'package:rate_limit/rate_limit.dart';
import 'package:flutter_flux/flutter_flux.dart';

class ThrottledStore extends Store {
  ...

  ThrottledStore(this._actions) : super.withTransformer(new Throttler(const Duration(milliseconds: 30))) {
    ...
  }
}

BONUS: Stores provide an optional terse syntax for action -> data mutation -> trigger operations.

// verbose syntax
actions.incrementCounter.listen(_handleAction);

_handleAction(payload) {
    // perform data mutation
    counter += payload;
    trigger();
  }

// equivalent terse syntax
triggerOnAction(actions.incrementCounter, (payload) => counter += payload);

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Examples

Simple examples of flutter_flux usage can be found in the example directory. The example README includes instructions for building / running them.

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External Consumption

flutter_flux implements a uni-directional data flow within an isolated application or code module. If flutter_flux is used as the internal architecture of a library, this internal data flow should be considered when defining the external API.

• External API methods intended to mutate internal state should dispatch Actions, just like any internal user interaction.
• External API methods intended to query internal state should leverage the existing read-only Store getter methods.
• External API streams intended to notify the consumer about internal state changes should be dispatched from the internal Stores, similar to their triggers.