public ContentItemViewModel() { Title = "DevDays Content Items"; ContentItems = new ObservableRangeCollection <Document>(); LoadCommand = new Command(async() => await ExecuteLoadDocumentsCommand()); MessagingCenter.Subscribe <NewContentTypePage, Document>(this, "AddContentItem", async(obj, document) => { var _document = document as Document; ContentItems.Add(_document); await DataStore.AddContentItemAsync(_document); }); }