viewmodel_widget_state.dart

typedef Widget EmptyBuilder();
typedef Widget Builder<T>(T state);

typedef R Mapper<R, S>(S state);
typedef void Handler<T>(T event);

abstract class ViewModelWidgetState<W extends StatefulWidget,
    S extends Cloneable<S>, VM extends StateViewModel<S>> extends State<W> {
  final List<StreamSubscription> _subscriptionsList =
      List<StreamSubscription>();
  List<DistinctStateNotifier> _stateNotifiers = List();

  S _state;

  Injector get injector => Injector();

  VM _viewModel;

  VM get viewModel {
    if (_viewModel == null)
      throw Exception("ViewModel was not created or is already disposed!");

    return _viewModel;
  }

  VM createViewModel();

  @override
  void initState() {
    _viewModel = createViewModel();

    if (_viewModel == null) {
      throw Exception("The viewmodel from type \"$VM\" is null");
    }

    //immediately set the initial state to avoid ui glitches
    //cause by the async delivery of states
    setState(() => _state = _viewModel.initialState);

    super.initState();

    _subscriptionsList.add(_viewModel.state.listen((state) {
      setState(() => _state = state);
      _onStateChanged(_state);
    }));

    afterViewModelInit();
  }

  Widget buildState(S state);

  Widget buildLoading() => Container();

  @override
  Widget build(BuildContext context) {
    if (_state != null) return buildState(_state);
    return buildLoading();
  }

  /**
   * Called after the initState - Can ensure that the VM is successfully created
   */
  void afterViewModelInit() {}

  @override
  void dispose() {
    _subscriptionsList.forEach((subscription) => subscription?.cancel());
    _viewModel.dispose();
    _viewModel = null;
    super.dispose();
  }

  void _onStateChanged(S state) =>
      _stateNotifiers.forEach((notifier) => notifier.onNewState(state));
}

hi, how would you do navigation in MVVM? I mean View knows context, but it is model that must decide there and when to go... Thanks.