async void ShowUnusedImage(CancellationTokenSource cts) { var unusedImageAttachList = await SendService.LoadUnusedAttachFilesAsync(cts); if (unusedImageAttachList != null && unusedImageAttachList.Count > 0) { if (AttachFileList == null) { AttachFileList = new ObservableCollection <AttachFileItemModel>(); } var list = AttachFileList.ToList(); foreach (var item in unusedImageAttachList) { if (list.Count(i => i.Id.Equals(item.Id)) == 0) { AttachFileList.Add(item); } } } }