public ReviewsViewModel(ICatalogueService catalogueService, INavigationService navigationService) : base(catalogueService, navigationService) { Messenger.Default.Register <long>(this, async(cId) => { SelectedCourseId = cId; IsLoadingProgressRing = true; ReviewsList = new ObservableCollection <CourReview>(await CatalogueService.GetCourseReviewByCourseId(cId)); IsLoadingProgressRing = false; IsNoReviewMessageVisible = (ReviewsList.Count > 0) ? Visibility.Collapsed : Visibility.Visible; }); }