A dart package that helps to implement basic states for BLoC library to perform, load and fetch data.

Features

• Provides all necessary states for data : init, waiting, value/no value and error states (from value_state),
• Provides BaseState.buildWidget that build a widget depending on its state. The WithValueState case is mandatory (first ordered parameter). Other states that are not passed as parameter are handled by ValueStateConfiguration. If no ValueStateConfiguration is in ascendant tree, a SizedBoxis returned,
• ValueStateConfiguration provides a default behavior for null parameters in BaseState.buildWidget.

Usage

This example show in the Flutter app, how pattern matching is used to handles the different states.

class CounterCubit extends ValueCubit<int> {
  var _value = 0;

  // Put your WS call that can be refreshed
  Future<int> _getCounterValueFromWebService() async => _value++;

  Future<void> increment() => perform(() async {
        // [perform] generate intermediate or final states such as PendingState,
        // concrete subclass of ReadyState with right [ReadyState.refreshing] value
        // or ErrorState if an error is raised.
        final result = await _getCounterValueFromWebService();

        emit(ValueState(result));
      });

  void clear() {
    _value = 0;
    emit(const PendingState());
  }
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return BlocProvider(
        create: (_) => CounterCubit(),
        child: MaterialApp(
          title: 'Value Cubit Demo',
          builder: (context, child) => child == null
              ? const SizedBox.shrink()
              : ValueStateConfiguration(
                  configuration: ValueStateConfigurationData(
                    builderWaiting: (context, state) =>
                        const Center(child: CircularProgressIndicator()),
                    builderError: (context, state) => Center(
                      child: Text('Expected error.',
                          style:
                              TextStyle(color: Theme.of(context).colorScheme.error)),
                    ),
                    builderNoValue: (context, state) =>
                        const Center(child: Text('No value.')),
                    wrapper: (context, state, child) => AnimatedSwitcher(
                        duration: const Duration(milliseconds: 300),
                        child: child),
                  ),
                  child: child,
                ),
          home: const MyHomePage(),
        ));
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({super.key});

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);

    return BlocBuilder<CounterCubit, BaseState<int>>(builder: (context, state) {
      return Scaffold(
        appBar: AppBar(
          title: const Text('Flutter Demo Home Page'),
        ),
        body: DefaultTextStyle(
          style: const TextStyle(fontSize: 24),
          textAlign: TextAlign.center,
          child: state.buildWidget(
              (context, state, error) => Column(
                      crossAxisAlignment: CrossAxisAlignment.stretch,
                      children: [
                        if (state.refreshing) const LinearProgressIndicator(),
                        const Spacer(),
                        if (error != null) error,
                        const Text('Counter value :'),
                        Text(
                          state.value.toString(),
                          style: theme.textTheme.headlineMedium,
                        ),
                        const Spacer(),
                      ]),
              valueMixedWithError: true),
        ),
        floatingActionButton: state is! ReadyState<int>
            ? null
            : FloatingActionButton(
                onPressed: state.refreshing
                    ? null
                    : context.read<CounterCubit>().increment,
                tooltip: 'Increment',
                child: state.refreshing
                    ? SizedBox.square(
                        dimension: 20,
                        child: CircularProgressIndicator(
                            color: theme.colorScheme.onPrimary))
                    : const Icon(Icons.refresh)),
      );
    });
  }
}

The whole code of this example is available in example.

Feedback

Please file any issues, bugs or feature requests as an issue on the Github page.