- Simple to learn, easy to use
- Handles complex applications with millions of users
- Testable
You'll be able to create apps much faster, and other people on your team will easily understand and modify your code.
An optimized reimagined version of Redux. A mature solution, battle-tested in hundreds of real-world applications. Created by Marcelo Glasberg (see all my packages).
There is also a version for React called Kiss State
Optionally use it with Provider or Flutter Hooks
The complete docs are published at https://asyncredux.com
Below is a quick overview.
The store holds all the application state. A few examples:
// Here, the state is a number
var store = Store<int>(initialState: 1);// Here, the state is an object
class AppState {
final String name;
final int age;
State(this.name, this.age);
}
var store = Store<AppState>(initialState: AppState('Mary', 25));
To use the store, add it in a StoreProvider at the top of your widget tree.
Widget build(context) {
return StoreProvider<int>(
store: store,
child: MaterialApp( ... ),
);
}
class MyWidget extends StatelessWidget {
Widget build(context) {
return Text('${context.state.name} has ${context.state.age} years old');
}
}
An action is a class that contain its own reducer.
class Increment extends Action {
// The reducer has access to the current state
int reduce() => state + 1; // It returns a new state
}
The store state is immutable.
The only way to change the store state is by dispatching an action. The action reducer returns a new state, that replaces the old one.
// Dispatch an action
store.dispatch(Increment());
// Dispatch multiple actions
store.dispatchAll([Increment(), LoadText()]);
// Dispatch an action and wait for it to finish
await store.dispatchAndWait(Increment());
// Dispatch multiple actions and wait for them to finish
await store.dispatchAndWaitAll([Increment(), LoadText()]);
The context extensions to dispatch actions are dispatch , dispatchAll etc.
class MyWidget extends StatelessWidget {
Widget build(context) {
return ElevatedButton(
onPressed: () => context.dispatch(Increment());
}
}
They download information from the internet, or do any other async work.
var store = Store<String>(initialState: '');class LoadText extends Action {
// This reducer returns a Future
Future<String> reduce() async {
// Download something from the internet
var response = await http.get('https://dummyjson.com/todos/1');
// Change the state with the downloaded information
return response.body;
}
}
If you want to understand the above code in terms of traditional Redux patterns, all code until the last
awaitin thereducemethod is the equivalent of a middleware, and all code after that is the equivalent of a traditional reducer. It's still Redux, just written in a way that is easy and boilerplate-free. No need for Thunks or Sagas.
If something bad happens, you can simply throw an error. In this case, the state will not change. Errors are caught globally and can be handled in a central place, later.
In special, if you throw a UserException, which is a type provided by Async
Redux,
a dialog (or other UI) will open automatically, showing the error message to the
user.
class LoadText extends Action {
Future<String> reduce() async {
var response = await http.get('https://dummyjson.com/todos/1');
if (response.statusCode == 200) return response.body;
else throw UserException('Failed to load');
}
}
To show a spinner while an asynchronous action is running, use
isWaiting(action).
To show an error message inside the widget, use isFailed(action).
class MyWidget extends StatelessWidget {
Widget build(context) {
if (context.isWaiting(LoadText)) return CircularProgressIndicator();
if (context.isFailed(LoadText)) return Text('Loading failed...');
return Text(context.state);
}
}
You can use dispatchAndWait to dispatch an action and wait for it to finish.
class LoadTextAndIncrement extends Action {
Future<AppState> reduce() async {
// Dispatch and wait for the action to finish
await dispatchAndWait(LoadText());
// Only then, increment the state
return state.copy(count: state.count + 1);
}
}
You can also dispatch actions in parallel and wait for them to finish:
class BuyAndSell extends Action {
Future<AppState> reduce() async {
// Dispatch and wait for both actions to finish
await dispatchAndWaitAll([
BuyAction('IBM'),
SellAction('TSLA')
]);
return state.copy(message: 'New cash balance is ${state.cash}');
}
}
You can also use waitCondition to wait until the state changes in a certain
way:
class SellStockForPrice extends Action {
final String stock;
final double limitPrice;
SellStockForPrice(this.stock, this.limitPrice);
Future<AppState?> reduce() async {
// Wait until the stock price is higher than the limit price
await waitCondition(
(state) => state.stocks[stock].price >= limitPrice
);
// Only then, post the sell order to the backend
var amount = await postSellOrder(stock);
return state.copy(
stocks: state.stocks.setAmount(stock, amount),
);
}
You can add mixins to your actions, to accomplish common tasks.
CheckInternet ensures actions only run with internet,
otherwise an error dialog prompts users to check their connection:
class LoadText extends Action with CheckInternet {
Future<String> reduce() async {
var response = await http.get('https://dummyjson.com/todos/1');
...
}
}
NoDialog can be added to CheckInternet so that no dialog is opened.
Instead, you can display some information in your widgets:
class LoadText extends Action with CheckInternet, NoDialog {
...
}
class MyWidget extends StatelessWidget {
Widget build(context) {
if (context.isFailed(LoadText)) Text('No Internet connection');
}
}
AbortWhenNoInternet aborts the action silently (without showing any dialogs)
if there is no internet connection.
To prevent an action from being dispatched while it's already running,
add the NonReentrant mixin to your action class.
class LoadText extends Action with NonReentrant {
...
}
Add the Retry mixin to retry the action a few times with exponential backoff,
if it fails. Add UnlimitedRetries to retry indefinitely:
class LoadText extends Action with Retry, UnlimitedRetries {
...
}
Add UnlimitedRetryCheckInternet to check if there is internet when you run
some action that needs it. If there is no internet, the action will abort
silently and then retried unlimited times, until there is internet. It will also
retry if there is internet but the action failed.
class LoadText extends Action with UnlimitedRetryCheckInternet {
...
}
The Throttle mixin prevents a dispatched action from running too often.
If the action loads information, the information is considered fresh.
Only after the throttle period ends is the information considered stale,
allowing the action to run again to reload the information.
class LoadPrices extends Action with Throttle {
final int throttle = 5000; // Milliseconds
Future<AppState> reduce() async {
var result = await loadJson('https://example.com/prices');
return state.copy(prices: result);
}
}
To limit how often an action occurs in response to rapid inputs, you can add
the Debounce mixin to your action class. For example, when a user types in
a search bar, debouncing ensures that not every keystroke triggers a server
request. Instead, it waits until the user pauses typing before acting.
class SearchText extends Action with Debounce {
final String searchTerm;
SearchText(this.searchTerm);
final int debounce = 300; // Milliseconds
Future<AppState> reduce() async {
var response = await http.get(
Uri.parse('https://example.com/?q=' + encoded(searchTerm))
);
return state.copy(searchResult: response.body);
}
}
To provide instant feedback on actions that save information to the server, this feature immediately applies state changes as if they were already successful, before confirming with the server. If the server update fails, the change is rolled back and, optionally, a notification can inform the user of the issue.
class SaveName extends Action with OptimisticUpdate {
async reduce() { ... }
}
Flutter widgets like TextField and ListView hold their own internal state.
You can use Events to interact with them.
// Action that changes the text of a TextField
class ChangeText extends Action {
final String newText;
ChangeText(this.newText);
AppState reduce() => state.copy(changeText: Event(newText));
}
}
// Action that scrolls a ListView to the top
class ScrollToTop extends Action {
AppState reduce() => state.copy(scroll: Event(0));
}
}
You can add a persistor to save the state to the local device disk.
var store = Store<AppState>(
persistor: MyPersistor(),
);
Just dispatch actions and wait for them to finish. Then, verify the new state or check if some error was thrown.
class AppState {
List<String> items;
int selectedItem;
}
test('Selecting an item', () async {
var store = Store<AppState>(
initialState: AppState(
items: ['A', 'B', 'C']
selectedItem: -1, // No item selected
));
// Should select item 2
await store.dispatchAndWait(SelectItem(2));
expect(store.state.selectedItem, 'B');
// Fail to select item 42
var status = await store.dispatchAndWait(SelectItem(42));
expect(status.originalError, isA<>(UserException));
});
If you are the Team Lead, you set up the app's infrastructure in a central place, and allow your developers to concentrate solely on the business logic.
You can add a stateObserver to collect app metrics, an errorObserver to log
errors,
an actionObserver to print information to the console during development,
and a globalWrapError to catch all errors.
var store = Store<String>(
stateObserver: [MyStateObserver()],
errorObserver: [MyErrorObserver()],
actionObservers: [MyActionObserver()],
globalWrapError: MyGlobalWrapError(),
For example, the following globalWrapError handles PlatformException errors
thrown
by Firebase. It converts them into UserException errors, which are built-in
types that
automatically show a message to the user in an error dialog:
Object? wrap(error, stackTrace, action) =>
(error is PlatformException)
? UserException('Error connecting to Firebase')
: error;
}
The Team Lead may create a base action class that all actions will extend, and add some common functionality to it. For example, getter shortcuts to important parts of the state, and selectors to help find information.
class AppState {
List<Item> items;
int selectedItem;
}
class Action extends ReduxAction<AppState> {
// Getter shortcuts
List<Item> get items => state.items;
Item get selectedItem => state.selectedItem;
// Selectors
Item? findById(int id) => items.firstWhereOrNull((item) => item.id == id);
Item? searchByText(String text) => items.firstWhereOrNull((item) => item.text.contains(text));
int get selectedIndex => items.indexOf(selectedItem);
}
Now, all actions can use them to access the state in their reducers:
class SelectItem extends Action {
final int id;
SelectItem(this.id);
AppState reduce() {
Item? item = findById(id);
if (item == null) throw UserException('Item not found');
return state.copy(selected: item);
}
}To learn more, the complete Async Redux documentation is published at https://asyncredux.com
glasberg.dev
github.com/marcglasberg
linkedin.com/in/marcglasberg/
twitter.com/glasbergmarcelo
stackoverflow.com/users/3411681/marcg
medium.com/@marcglasberg
I wrote Google's official Flutter documentation on layout rules:
The Flutter packages I've authored:
- async_redux
- provider_for_redux
- i18n_extension
- align_positioned
- network_to_file_image
- image_pixels
- matrix4_transform
- back_button_interceptor
- indexed_list_view
- animated_size_and_fade
- assorted_layout_widgets
- weak_map
- themed
- bdd_framework
- tiktoken_tokenizer_gpt4o_o1
The JavaScript/TypeScript packages I've authored:
- Kiss State, for React (similar to Async Redux, but for React)
- Easy BDD Tool, for Jest
My Medium Articles: