b3-acharcode.dart

    abstract class CounterEvent {}

    class Increment extends CounterEvent {}

    class CounterBloc extends Bloc<CounterEvent, int> {
      CounterBloc() : super(0) {
        on<Increment>((event, emit) => emit(state + 1));
      }

      @override
      void onEvent(CounterEvent event) {
        super.onEvent(event);
        print(event);
      }

      @override
      void onChange(Change<int> change) {
        super.onChange(change);
        print(change);
      }

      @override
      void onTransition(Transition<CounterEvent, int> transition) {
        super.onTransition(transition);
        print(transition);
      }

      @override
      void onError(Object error, StackTrace stackTrace) {
        print('$error, $stackTrace');
        super.onError(error, stackTrace);
      }
    }