public async Task <DlVersionChangeHistoryResponse> GetDlBookChangeHistory(int bookId, int lastDownloadedVersion, string email, string deviceId) { DlVersionChangeHistoryRequest dlVersionChangeHistory = new DlVersionChangeHistoryRequest { DeviceId = deviceId, DlId = bookId, Email = email, Ver = lastDownloadedVersion }; var changeHistoryResult = await deliveryService.DlVersionChangeHistory(dlVersionChangeHistory); DlVersionChangeHistoryResponse dlBookChangeHistory = null; if (changeHistoryResult.IsSuccess) { dlBookChangeHistory = JsonConvert.DeserializeObject <DlVersionChangeHistoryResponse>(changeHistoryResult.Content); } return(dlBookChangeHistory); }