counter bloc for medium blog

counter_bloc.dart

import 'dart:async';

// those are the events that the user can do,
// aka `add` to the bloc and manipulate the bloc state.
enum CounterEvent {
  increment,
  decrement,
  reset,
}

class CounterBloc {
  late int _counter;

  final _stateStreamController = StreamController<int>();
  final _eventStreamController = StreamController<CounterEvent>();

  // should only be used inside the bloc.
  StreamSink<int> get _stateSink => _stateStreamController.sink;
  // this will be listened to in the ui to change the ui accordingly.
  Stream<int> get stateStream => _stateStreamController.stream;

  // this will be used to interact with the bloc and manipulate it from the ui.
  StreamSink<CounterEvent> get eventSink => _eventStreamController.sink;
  // should only be used inside the bloc.
  Stream<CounterEvent> get _eventStream => _eventStreamController.stream;

  CounterBloc() {
    // this is the inital state.
    _counter = 0;

    // here we listen to the events stream and run some logic on the state
    // according to the event provided.
    _eventStream.listen((CounterEvent event) {
      if (event == CounterEvent.increment) {
        _counter++;
      } else if (event == CounterEvent.decrement) {
        _counter--;
      } else if (event == CounterEvent.reset) {
        _counter = 0;
      }

      // the new counter is added to state after the manipulation.
      // this will be reflected in the ui.
      _stateSink.add(_counter);
    });
  }
}

counter_screen_buttons.dart

// ... other widgets in the column.

Row(
  mainAxisAlignment: MainAxisAlignment.spaceAround,
  children: <Widget>[
    IconButton(
      onPressed: () {
        // add decrement event to counter bloc.
        _counterBloc.eventSink.add( // add this line
          CounterEvent.decrement, // add this line
        ); // add this line
      },
      icon: const Icon(
        Icons.remove_rounded,
      ),
    ),
    IconButton(
      onPressed: () {
        // add reset event to counter bloc.
        _counterBloc.eventSink.add( // add this line
          CounterEvent.reset, // add this line
        ); // add this line
      },
      icon: const Icon(
        Icons.restore_rounded,
      ),
    ),
    IconButton(
      onPressed: () {
        // add increment event to counter bloc.
        _counterBloc.eventSink.add( // add this line
          CounterEvent.increment, // add this line
        ); // add this line
      },
      icon: const Icon(
        Icons.add_rounded,
      ),
    ),
  ],
),

// the rest of the build method ...

counter_screen_init_bloc.dart

// ... stateful widget and other stuff.

class _CounterScreenState extends State<CounterScreen> {
  late final CounterBloc _counterBloc; // add this line

  @override
  void initState() {
    super.initState();

    // initialze counter bloc.
    _counterBloc = CounterBloc(); // add this line
  }

// build method and other stuff...
}

counter_screen_stream_builder.dart

// ... other widgets in the column.

StreamBuilder<int>(
  stream: _counterBloc.stateStream,
  builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
    final int counter = snapshot.data ?? 0;

    return Text(
      "$counter",
      style: const TextStyle(
        color: Colors.black54,
        fontWeight: FontWeight.bold,
        fontSize: 48,
      ),
      textAlign: TextAlign.center,
    );
  },
),

// other widgets in the column ...