RemoteState

Build & test codecov License: MIT

Tools for mapping data from remote sources in Dart, similar to Elm's RemoteData: https://elmprogramming.com/remote-data.html

PackagePub
remote_statepub package

Slaying a UI Antipattern with Flutter.

Library inspired by a blog post by Kris Jenkins about How Elm slays a UI antipattern.

What problem does this package solve?

You are making an API request, and you want to display or do different things based on the status of the request.

Why RemoteState, not RemoteData?

I gained secondary inspiration from a talk by Jed Watson, A Treatise on State. As much as possible, I try to categorize state correctly in my applications.

The RemoteState approach

Instead of using a complex object we use a single data type to express all possible request states. This approach makes it impossible to create invalid states.

Usage

A common use case for RemoteState would be mapping it into a UI transition or component state. Here is an example that uses StateNotifier, found in examples/counter_state_notifier

counter/notifier/counter.dart


class CounterNotifier extends StateNotifier<RemoteState<int>> {
  var _counterClient = CounterClient();

  CounterNotifier() : super(RemoteState.initial()) {
    getCount();
  }

  getCount() async {
    state = RemoteState.loading();

    state = await RemoteState.guard(() => _counterClient.getCount());
  }

  increment() async {
    state = await RemoteState.guard(() => _counterClient.increment());
  }

  decrement() async {
    state = await RemoteState.guard(() => _counterClient.decrement());
  }
}

main.dart

class ExampleApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: StateNotifierProvider<CounterNotifier, RemoteState<int>>.value(
        value: CounterNotifier(),
        child: HomePage(),
      ),
    );
  }
}

home.dart

class HomePage extends StatelessWidget {
  const HomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    //2. Resolve counter notifier to update state
    var counterNotifier = Provider.of<CounterNotifier>(context);
    var counterState = Provider.of<RemoteState<int>>(context);

    var textStyle = Theme.of(context).textTheme.display1;
    final fabPadding = EdgeInsets.symmetric(vertical: 5.0);

    return Scaffold(
      appBar: AppBar(
        title: Text('RemoteState with StateNotifier'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('You have pushed the button this many times:'),
            //3. Render state changes
            counterState.when(
              initial: () => Text('Not loaded', style: textStyle),
              success: (value) => Text('$value', style: textStyle),
              loading: () => Text('Loading...', style: textStyle),
              error: (_) => Text('Error', style: textStyle),
            ),
          ],
        ),
      ),
      floatingActionButton: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          Padding(
            padding: fabPadding,
            child: FloatingActionButton(
              heroTag: 'inc',
              child: Icon(Icons.add),
              //4. Perform increment action
              onPressed: () => counterNotifier.increment(),
            ),
          ),
          Padding(
            padding: fabPadding,
            child: FloatingActionButton(
              heroTag: 'dec',
              child: Icon(Icons.remove),
              //5. Perform decrement action
              onPressed: () => counterNotifier.decrement(),
            ),
          ),
        ],
      ),
    );
  }
}

API

RemoteState

RemoteState<T> is usedto annotate your request variables. It wraps all possible request states into one single union type. Use the parameters to specify.

  • T: The success value type.

RemoteState.initial

RemoteState.initial is an instance of RemoteState that signifies the request hasn't been made yet.

RemoteState.loading

RemoteState.loading is an instance of RemoteState that signifies the request has been made, but it hasn't returned any data yet.

RemoteState.success

RemoteState.success is an instance of RemoteState that signifies the request has completed successfully and the new data (of type T) is available.

RemoteState.error

RemoteState.error is an instance of RemoteState that signifies the request has failed.

RemoteState.guard

RemoteState.guard is a static function that converts a Future to RemoteState. It will emit RemoteState.error if the future fails or RemoteState.success if the future completes.

Pattern matching high order functions

When

The when method is a high order function that accepts a method for each state and matches the request state with the appropriate callback function. All callbacks are required and must not be null.

MaybeWhen

The maybeWhen method is a high order function that accepts a method for each state and matches the request state with the appropriate callback function or a fallback callback for missing methods. Only orElse is required.

Map

The map method is the equivalent of when without the destructuring.

MaybeMap

The maybeWhen method is the equivalent of when without the destructuring.

State Predicates

isInitial

The isInitial predicate returns true if we haven't asked for data yet.

isLoading

The isLoading predicate returns true if we're loading.

isSuccess

The isSuccess predicate returns true if we've successfully loaded some data.

isError

The isError predicate returns true if we've failed to load some data.

Maintainers

References

Libraries

remote_state