private async void ShowOverlayIfBookDownloading()
        {
            if (CheckIsDownloading())
            {
                _busyOverlay.Closing -= GoBack;
                _busyOverlay.Closing += GoBack;
                await _busyOverlay.Start(false);

                IsBusy = true;
            }
            else if (StartDownload)
            {
                StartDownload = false;
                DownloadBook(true);
            }
        }
        public async void ShareAsync()
        {
            if (Book == null)
            {
                return;
            }

            if (!await SharingDataModel.ShowMessage())
            {
                return;
            }

            _busyOverlay.Closable = true;
            _busyOverlay.Content  = UIStrings.BookInfoPage_Loading;
            _busyOverlay.Closing += Cancel;
            using (await _busyOverlay.Start())
            {
                await SharingDataModel.UploadBook(Book);
            }
        }