ReplayBloc

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An extension to package:bloc which adds automatic undo and redo support to bloc and cubit states. Built to work with package:bloc.

Learn more at bloclibrary.dev!

Creating a ReplayCubit

class CounterCubit extends ReplayCubit<int> {
  CounterCubit() : super(0);

  void increment() => emit(state + 1);
}

Using a ReplayCubit

void main() {
  final cubit = CounterCubit();

  // trigger a state change
  cubit.increment();
  print(cubit.state); // 1

  // undo the change
  cubit.undo();
  print(cubit.state); // 0

  // redo the change
  cubit.redo();
  print(cubit.state); // 1
}

ReplayCubitMixin

If you wish to be able to use a ReplayCubit in conjuction with a different type of cubit like HydratedCubit, you can use the ReplayCubitMixin.

class CounterCubit extends HydratedCubit<int> with ReplayCubitMixin {
  CounterCubit() : super(0);

  void increment() => emit(state + 1);
  void decrement() => emit(state - 1);

  @override
  int fromJson(Map<String, dynamic> json) => json['value'] as int;

  @override
  Map<String, int> toJson(int state) => {'value': state};
}

Creating a ReplayBloc

class CounterEvent extends ReplayEvent {}

class Increment extends CounterEvent {}

class Decrement extends CounterEvent {}

class CounterBloc extends ReplayBloc<CounterEvent, int> {
  CounterBloc() : super(0);

  @override
  Stream<int> mapEventToState(CounterEvent event) async* {
    if (event is Increment) {
      yield state + 1;
    } else if (event is Decrement) {
      yield state - 1;
    }
  }
}

Using a ReplayBloc

void main() {
  // trigger a state change
  final bloc = CounterBloc()..add(Increment());

  // wait for state to update
  await bloc.first;
  print(bloc.state); // 1

  // undo the change
  bloc.undo();
  print(bloc.state); // 0

  // redo the change
  bloc.redo();
  print(bloc.state); // 1
}

ReplayBlocMixin

If you wish to be able to use a ReplayBloc in conjuction with a different type of cubit like HydratedBloc, you can use the ReplayBlocMixin.

abstract class CounterEvent with ReplayEvent {}

class Increment extends CounterEvent {}

class Decrement extends CounterEvent {}

class CounterBloc extends HydratedBloc<CounterEvent, int> with ReplayBlocMixin {
  CounterBloc() : super(0);

  @override
  Stream<int> mapEventToState(CounterEvent event) async* {
    if (event is Increment) {
      yield state + 1;
    } else if (event is Decrement) {
      yield state - 1;
    }
  }

  @override
  int fromJson(Map<String, dynamic> json) => json['value'] as int;

  @override
  Map<String, int> toJson(int state) => {'value': state};
}

Dart Versions

  • Dart 2: >= 2.6.0

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Libraries

replay_bloc