public async void ContinueFileOpenPicker(IReadOnlyList<StorageFile> files)
        {
            if (files == null || !files.Any()) return;
            IsLoading = true;
            using (var stream = (FileRandomAccessStream)await files[0].OpenAsync(FileAccessMode.Read))
            {
                var newImageBytes = new byte[stream.Size];
                using (var dataReader = new DataReader(stream))
                {
                    await dataReader.LoadAsync((uint)stream.Size);
                    dataReader.ReadBytes(newImageBytes);
                }

                var contentHelper = new ContentClientHelper(QuickbloxClient);
                var blobUploadInfo = await contentHelper.UploadImage(newImageBytes, false);
                if (blobUploadInfo != null)
                {
                    SendAttachment(blobUploadInfo);
                }
            }
            IsLoading = false;
        }