public UpdateCurrentViewModelCommand(
     INavigator navigator,
     ISimpleTraderViewModelAbstractFactory viewModelFactory)
 {
     _navigator        = navigator;
     _viewModelFactory = viewModelFactory;
 }
 public Navigator(ISimpleTraderViewModelAbstractFactory viewModelFactory)
 {
     UpdateCurrentViewModelCommand = new UpdateCurrentViewModelCommand(this, viewModelFactory);
 }