reactive_state

An easy to understand reactive state management solution for Flutter.

Principles

Observable state

State is held in one or multiple instances of Value or similar classes implementing ValueNotifier. These are standard Flutter interfaces that everybody knows from TextEditingController, Animation, etc.

Additionally, you can use ListValue and MapValue for creating observable List and Map values that can notify you about fine-grained change events (instead of the whole value changing).

Reactive widgets

AutoBuild automatically rebuilds your widgets when a ValueNotifier (or any Listenable) triggers a notification. It's similar to Flutter's ValueListenableBuilder, but it can track multiple dependencies and also works with Listenable.

No need to call addListener/removeListener. Just get() the value directly while AutoBuild takes care of tracking your dependencies.

Unlike InheritedWidget and Provider you get fine-grained control over what gets rebuilt.

Standard Flutter classes like TextEditingController and Animation implement ValueListenable and thus work nicely with AutoBuild.

Derived/computed state

DerivedValue is an observable value that is computed (derived) from other observable values.

Also, ListValue and MapValue provide .map() and other operations for creating derived containers that keep themselves updated on a per-element basis.

Less boilerplate and indirection

The resulting code is much simpler than the same solution in BLoC or Redux.

• No streams, no StreamBuilder, no asynchronous loading of widgets (unless you really need it).
• No special event objects, no event handlers with long switch() statements.

Usage

Note: Also see reference for details.

A simple AutoBuild example:

import 'package:flutter/material.dart';
import 'package:reactive_state/reactive_state.dart';

class MyPage extends StatelessWidget {
  MyPage({Key key, @required this.counter}) : super(key: key);

  final ValueNotifier<int> counter;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Counter')),
      body: Column(
        children: <Widget>[
          AutoBuild(builder: (context, get, track) {
            return Text('Counter: ${get(counter)}');
          }),
          MaterialButton(
            onPressed: () => counter.value++,
            child: Text('Increment'),
          ),
        ],
      ),
    );
  }
}

Note that in real-world applications you shouldn't directly mutate the state, but instead put that into separate methods e.g. on an object made accessible through the provider package.

Also, take a look at the example in the repo.

autoRun and AutoRunner

Outside of widgets you might still want to react to state changes. You can do that with autoRun() and AutoRunner (see reference for details).

Value vs ValueNotifier

As an alternative to ValueNotifier you can also use reactive_state's Value class which provides an update() method for modifying more complex objects:

class User {
  String name = '';
  String email = '';
  // ...
}

var userValue = Value(User());
userValue.update((user) {
  user.name = 'Adam';
  user.email = '[email protected]';
});

This is similar to calling setState() with StatefulWidget. With update() you can change multiple attributes and Value will trigger a single notification once finished - even if nothing was changed (so you don't need to implement comparison operators for complex objects).

DerivedValue

DerivedValue is a dynamically calculated ValueListenable that updates its value whenever its dependencies change:

var user = Value(User());
var emailLink = DerivedValue((get, track) => 'mailto:${get(user).email}');

Here, emailLink can be observed on its own and is updated whenever user is modified.

ListValue and MapValue

A simple example showing a few things that can be done:

final listValue = ListValue(<int>[]);
final mappedList = listValue.map((x) => x.toString());
final listToMap = mappedList.toMap((x) => MapEntry(2 * int.parse(x), x));
final invertedMap = listToMap.map((k, v) => MapEntry(v, k));

listValue.addAll([4, 1]);
// => invertedMap.value == {'4': 8, '1': 2}