Dart - BlocCounter Example

main.dart

import 'dart:async';

enum CounterEvent {increment, decrement}

class CounterBloc {
  int _counter = 0;
  
  get state => _counter;
  
  final _counterStateController = StreamController<int>();
  StreamSink<int> get _inCounter => _counterStateController.sink;
  
  Stream<int> get counter => _counterStateController.stream;
  
  final _counterEventController = StreamController<CounterEvent>();
  
  Sink<CounterEvent> get counterEventSink => _counterEventController.sink;
  
  CounterBloc() {
    _counterEventController.stream.listen(_mapEventToState);
  }
                                          
  void _mapEventToState(CounterEvent event) {
     if (event == CounterEvent.increment) {
        _counter++;
      } else if (event == CounterEvent.decrement) {
        _counter--;
      }
      _inCounter.add(_counter);
  }                                    
  
  dispose() {
    _counterStateController.close();
    _counterEventController.close();
  }
}

var decorateCounter = StreamTransformer<int, String>.fromHandlers(handleData: (int val, EventSink<String>sink) => {
  sink.add('New counter is $val')
});

void main() {
  final counterBloc = CounterBloc();
  counterBloc.counter
    .transform(decorateCounter)
    .listen((val) => print(val));
  counterBloc.counterEventSink.add(CounterEvent.increment);
  counterBloc.counterEventSink.add(CounterEvent.decrement);
  counterBloc.counterEventSink.add(CounterEvent.increment);
  print(counterBloc.state);
}