Channel9Downloader.DataAccess.DownloadManager.DownloadFileAsync C# (CSharp) Method

        private Task<object> DownloadFileAsync(
            string address,
            string filename,
            IDownloadItem downloadItem,
            CancellationToken token)
        {
            var tcs = new TaskCompletionSource<object>();
            var webClient = _composer.GetExportedValue<IWebDownloader>();

            token.Register(webClient.CancelAsync);

            webClient.DownloadFileCompleted += (obj, args) =>
            {
                if (args.Cancelled)
                {
                    tcs.TrySetCanceled();
                    downloadItem.DownloadState = DownloadState.Stopped;
                    return;
                }

                if (args.Error != null)
                {
                    tcs.TrySetException(args.Error);
                    downloadItem.DownloadState = DownloadState.Error;
                    return;
                }

                tcs.TrySetResult(null);
                downloadItem.DownloadState = DownloadState.Finished;
            };

            webClient.DownloadProgressChanged += (obj, args) =>
            {
                downloadItem.ProgressPercentage = args.ProgressPercentage;
                downloadItem.BytesReceived = args.BytesReceived;
                downloadItem.TotalBytesToReceive = args.TotalBytesToReceive;
            };

            try
            {
                webClient.DownloadFileAsync(new Uri(address), filename);
                downloadItem.DownloadState = DownloadState.Downloading;
            }
            catch (UriFormatException ex)
            {
                tcs.TrySetException(ex);
            }

            return tcs.Task;
        }