[bloc_package] counter bloc w/ onTransition

counter_bloc.dart

enum CounterEvent { increment, decrement }

class CounterBloc extends Bloc<CounterEvent, int> {
  @override
  int get initialState => 0;
  
  @override
  void onTransition(Transition<CounterEvent, int> transition) {
    print(transition);
  }

  @override
  Stream<int> mapEventToState(CounterEvent event) async* {
    switch (event) {
      case CounterEvent.decrement:
        yield currentState - 1;
        break;
      case CounterEvent.increment:
        yield currentState + 1;
        break;
    }
  }
}