management 0.0.4

Simple and easy to use state management solution for Flutter.

This package is a small and easy to use state management solution for Flutter.

Pattern

• There are four classes: Managed, Manager, State and Effect.
• Managed is extended by the widget. It overrides listener and builder functions.
• listener is responsible for handling Effects, like showing a snackbar, navigating to the next screen, etc.
• buidler is responsible for building the widget based on State, which may contain an index of a counter, a loading state of a button, etc.
• Manager is responsible for all the UI logic while emitting states and publishing effects.

Prerequisites

This packaged is currently designed to work on a project with certain conditions:

• The project must use auto_route for navigation.
• The project must use get_it with injectable for dependency injection.
• The project must use freezed.

Getting started

To install the package, include the git repository in your pubspec.yaml:

management:
   git: https://github.com/imnadev/management.git

To generate a managed page in your presentation directory, run this command in your terminal and give it a name of home when prompted:

dart run management:generate lib/presentation/

Package Usage

home_management.dart contains HomeState and HomeEffect. HomeState holds the current state of the widget. HomeEffect is used to fire side effects to the widget.

@freezed
abstract class HomeState with _$HomeState {
  const factory HomeState({
    @Default(0) int counter,
    @Default(false) bool loading,
  }) = _HomeState;
}

@freezed
sealed class HomeEffect with _$HomeEffect {
  const factory HomeEffect.reminder({required int dozen}) = Reminder;
}

home_manager.dart is where state management logic resides. It may call emit with a copy of current HomeState or publish with a new instance of HomeEffect.

@injectable
class HomeManager extends Manager<HomeState, HomeEffect> {
  HomeManager() : super(const HomeState());

  void startWith(int count) {
    emit(state.copyWith(counter: count));
  }

  Future<void> increment() => Future.delayed(const Duration(seconds: 1))
      .then((_) => state.counter + 1)
      .handle(
        onStart: () => emit(state.copyWith(loading: true)),
        onData: (data) {
          emit(state.copyWith(counter: data));
          if (state.counter % 12 == 0) {
            publish(HomeEffect.reminder(dozen: state.counter ~/ 12));
          }
        },
        onDone: () => emit(state.copyWith(loading: false)),
      );
}

home_page.dart is where the Managed widget lies. It overrides the builder funciton which is called whenever the state changes. It may also override init which is called during initState and listener which is called when an effect is published.

class HomePage extends Managed<HomeManager, HomeState, HomeEffect> {
  const HomePage({super.key});

  @override
  void init(context, manager) {
    manager.startWith(10);
  }

  @override
  void listener(context, manager, effect) {
    switch (effect) {
      case Reminder():
        final message =
            'You have pushed the button ${effect.dozen} dozen times';
        final snackBar = SnackBar(content: Text(message));
        ScaffoldMessenger.of(context).showSnackBar(snackBar);
        break;
    }
  }

  @override
  Widget builder(context, manager, state) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              state.counter.toString(),
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: manager.increment,
        child: const Icon(Icons.add),
      ),
    );
  }
}