public MasterViewModel( IDataService dataService, IEventAggregator eventAggregator, IRegionManager regionManager )
{
_dataService = dataService;
_eventAggregator = eventAggregator;
_regionManager = regionManager;
// Get the data model from the data service.
_model = dataService.GetModel();
// Initialize the CollectionView for the underlying model.
DataItemsCV = new ListCollectionView( _model );
// Track the current selection.
DataItemsCV.CurrentChanged += new EventHandler( SelectedItemChanged );
// Initialize the commands.
NavigateToViewCommand = new DelegateCommand<string>( NavigateToView );
SyncViewCommand = new DelegateCommand<string>( SyncView );
}