public ContentTypeViewModel()
        {
            Title        = "DevDays Content Types";
            ContentTypes = new ObservableRangeCollection <Document>();
            LoadCommand  = new Command(async() => await ExecuteLoadDocumentsCommand());

            MessagingCenter.Subscribe <NewContentTypePage, Document>(this, "AddContentType", async(obj, contentType) =>
            {
                var _contentType = contentType;
                if (_contentType == null)
                {
                    return;
                }

                ContentTypes.Add(_contentType);
                await DataStore.AddContentTypeAsync(_contentType);
            });
        }