stream_example.dart

// Widget class

@override initState() {
  AppStateBloc.stream.listen(updateWidget); // Subscribe to the state stream
}

void updateWidget(AppState obj) {
  setState(() {}); // Trigger rebuild
}

void mutateState() { // Simulates doing something that would cause the state to change
  AppStateBloc.dispatch('changeInteger', 2);
}

@override Widget build(BuildContext cxt) {
  final state = AppStateBloc.currentState; // Get the current state
  // ... 
  // Build widget based on the values from state
}

// ..........

// AppStateBloc class

// The data object representing the current state
// This object can have any number of fields of all sorts of types
AppState _currentState;
AppState get currentState => _currentState;

_StreamController<AppState> _controller; // Responsible for piping items to the stream
Stream<AppState> get stream => _controller.stream; // Convenience getter so widgets can listen to the stream

// This method handles change requests to the stream
void dispatch(String label, dynamic value) async {
  await for (var value in _updateState()) {
    // For every value we get back from _updateState, change the current state and fire the stream event
    currentState = value;
    _controller.add(value);
  }
}

// An internal helper method for handling state change requests
Stream<AppState> _updateState(String label, dynamic value) async* {
  // Handle the state change depending on the label passed
  //
  // Note that some changes involve updating the state object multiple times,
  // causing the stream to receive multiple updates from a single call.
  switch (label) {
    case 'changeInteger':
      yield currentState.copyWith(intValue: value);
      break;
    
    case 'changeString':
      yield currentState.copyWith(stringValue: value);
      break;
    
    case 'changeBool':
      yield currentState.copyWith(boolValue: value);
      break;
    
    case 'makeComplexChanges':
      yield currentState.copyWith(complexValueA: value.a);
      yield currentState.copyWith(complexValueB: value.b);
      yield currentState.copyWith(complexValueC: value.c);
      break;
  }
}