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Extension to ValueNotifier by transparently applying functional reactive programming (TFRP)

rx_notifier #

The ValueNotifier is a simple, native form of Flutter reactivity. This extension aims to transparently apply functional reactive programming (TFRP).

Install #

flutter pub add rx_notifier

Understanding Extension. #

This extension adds a class RxNotifier and a converter ValueNotifier -> RxNotifier so that it can be observed transparently by the function rxObserver() and Widget RxBuilder.

The RxNotifier is directly an extension of ValueListenable then any object that implements it can be converted to RxNotifier

The only difference from RxNofifier to ValueNotifier is the automatic signature function in Observers rxObserver() e RxBuilder, very similar to MobX reactions.

Using #

To start, instantiate an RxNofifier.

final counter = RxNotifier<int>(0);

or convert a ValueNotifier already existing using the .rx() method:

final counter = myValueNotifierCounter.asRx();

IMPORTANT: The asRx() method has been added to ValueNotifier using Extension Methods.

And listen the changes using rxObserver:

RxDisposer disposer = rxObserver((){


All declared values in the current scope fn() are observables and can generate a value that is listened in property effect.

RxDisposer disposer = rxObserver<String>((){
    return '${name.value} + ${lastName.value}';
}, effect: (String fullName){


This is the transparent use of individual reactivity, but we can also combine RxNotifier Objects producing new value. This technique is called Computed

Computed: Combining reactive values #

To combine two or more RxNotifier Objects we need to use a getter returning a new combined value:

final num1 = RxNotifier<int>(1);
final num2 = RxNotifier<int>(2);

String get result => 'num1: ${num1.value} + num2: ${num2.value} = ${num1.value + num2.value}';


    print(result); // print´s "num1: 1 + num2: 2 = 3

IMPORTANT: It is really necessary that computed are Getters and not assignments. The reaction will happen when any of the RxNotifier changes the value.

Using Getters #

We can also use getters in reactive values making, let's repeat the example above:

final _num1 = RxNotifier<int>(1);
int get num1 => _num1.value;

final _num2 = RxNotifier<int>(2);
int get num2 => _num2.value;

String get result => 'num1: $num1 + num2: $num2 = ${num1 + num2}';


    print(result); // print´s "num1: 1 + num2: 2 = 3

Filters #

All Rx listeners have a property filter filter which is a function that returns a bool. Use this to define when (or not) to reflect changes:

RxDisposer disposer = rxObserver<String>((){
    return '${name.value} + ${lastName.value}';
}, filter: (fullName) => fullName.isNotEmpty);


Flutter and RxNotifier #

RxNotifeir has tools that help with state management and propagation for the Widget.

  1. Add the RxRoot Widget to the root of the app:
void main(){
  runApp(RxRoot(child: AppWidget()));
  1. Now just use the context.select method passing the RxNotifier objects:

final counter = RxNotifier(0);

class HomePage extends StatelessWidget {
  Widget build(BuildContext context) {
    final value = context.select(() => counter.value);

    return Scaffold(
      body: Center(
        child: Text(
           style: TextStyle(fontSize: 23),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: () => counter.count++,
  1. To execute methods that call something external to the state like [Dialog], [SnackBar] and etc, use context.callback to listen for one or several [RxNotifier] subscribing to a callback.

  Widget build(BuildContext context) {
    context.callback(() => errorState.value, _showSnachbar);


Widgets: RxBuilder #

A builder for managing state in a scoped way is also available:

Widget build(BuildContext context){
    return RxBuilder(
        builder: (_) => Text('${counter.value}'),

IMPORTANT: Both the context.select method and the builder have the filter property.

Widgets: RxCallback #

This widget can replace context.callback by getting a product list from rxObserver.

Widget build(BuildContext context){
    return RxCallback(
        effects: [
          rxObserver(() => errorState.value, effect: _showSnachbar)
        child: BodyWidget(),

Collections and Asyncs #


An RxList gives you a deeper level of observability on a list of values. It tracks when items are added, removed or modified and notifies the observers. Use an RxList when a change in the list matters.


An RxMap gives you a deeper level of observability on a map of values. It tracks when keys are added, removed or modified and notifies the observers. Use an RxMap when a change in the map matters.


An RxSet gives you a deeper level of observability on a set of values. It tracks when values are added, removed or modified and notifies the observers. Use an RxSet when a change in the set matters.


The RxFuture is the reactive wrapper around a Future. You can use it to show the UI under various states of a Future, from pending to fulfilled or rejected. The status, result and error fields of an RxFuture are observable and can be consumed on the UI. You can add a new Future using .value

final rxFuture = RxFuture.of(myFuture);

rxFuture.value = newFuture;


The stream that is tracked for status and value changes. T initialValue: The starting value of the stream.

OPTIONAL Code generator #

If you prefer a leaner syntax for RxNotifier objects, use code generation with build_runner.

  1. Add the rx_notifier_generator and build_runner packages to dev_dependencies.
  rx_notifier_generator: <current-version>
  build_runner: <current-version>
  1. Use the @RxStore annotation on the class and @RxValue on the properties.
part 'app_store.g.dart';

abstract class _AppStore {
  int count = 0;

  String name = 'Barney';
  1. Run the build runner:
dart pub run build_runner --delete-conflicting-outputs
  1. Just use:
final appStore = AppStore();


appStore.count++; // update

  1. The class that will be annotated with @RxStore must be abstract and private. The generator will start a public instance with transparent RxNotifier.

  2. Properties with @RxValue must be mutable and public.

Features and bugs #

Please send feature requests and bugs at the issue tracker.

This README was created based on templates made available by Stagehand under a BSD-style license.

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verified publisherflutterando.com.br

Extension to ValueNotifier by transparently applying functional reactive programming (TFRP)

Repository (GitHub)
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API reference




collection, flutter, rx_notifier_annotation


Packages that depend on rx_notifier