private async void DownloadBlob(CloudBlobContainer container, string fileName, int fileId, long fileSize)
        {
            StorageFolder pictureFolder = KnownFolders.PicturesLibrary;
            StorageFile   file          = await pictureFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);

            using (var fileStream = await file.OpenStreamForWriteAsync())
            {
                // Retrieve reference to a blob
                CloudBlockBlob      blob           = container.GetBlockBlobReference(fileName);
                Stream              stream         = new MemoryStream();
                AzureProgressStream progressStream = new AzureProgressStream(stream);
                progressStream.ProgressChanged += pstream_ProgressChanged;
                progressStream.SetLength(fileSize);
                progressStream.FileId = fileId;
                IOutputStream outputStream = WindowsRuntimeStreamExtensions.AsOutputStream(progressStream);
                await blob.DownloadToStreamAsync(outputStream);

                stream.Position = 0;
                stream.CopyTo(fileStream);
                fileStream.Flush();
            }
        }