Download code with cancelation support

    53
		private async void btnDownload_Click(object sender, RoutedEventArgs e)
        {
             DownloadBookAsync(file_url);
		}

	   private async void DownloadBookAsync(String url)
       {
            cts = new CancellationTokenSource();
            Problem fileDownloaded = await DownloadFileFromWeb(url, cts.Token);
            switch (fileDownloaded)
            {
                case Problem.Ok:
                    MessageBox.Show("OK");
                    break;
                case Problem.Cancelled:
                     MessageBox.Show("Canceled");
                    break;
                case Problem.Other:
                default:
                     MessageBox.Show("Other problem with download");
                    break;
            }
        }

        // first define Cancellation Token Source - I've made it global so that CancelButton has acces to it
        public CancellationTokenSource cts = new CancellationTokenSource();
        public enum Problem { Ok, Cancelled, Other }; // results of my Task
        // the main method - I've described it a little below in the text
        public async Task<Problem> DownloadFileFromWeb(string item, CancellationToken cToken)
        {
            try
            {
                //get zipfile data
                using (Stream response_stream = await DownloadHpubFile(new Uri(item)))
                using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication())
                {
                    //Save zipfile data
                    if (!file.DirectoryExists("FolderRoor/Files"))
                    {
                        file.CreateDirectory("FolderRoor/Files");
                    }
                    string dir = "/FolderRoor/Files/" + item.Trim();
                    using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream(dir, System.IO.FileMode.OpenOrCreate, FileAccess.ReadWrite, file))
                    {
                        byte[] buffer = new byte[1024];
                        while (response_stream.Read(buffer, 0, buffer.Length) > 0) //Getting exception here now
                        {
                            stream.Write(buffer, 0, buffer.Length);
                        }
                    }
                }
                return Problem.Ok;
            }
            catch (Exception exc)
            {
                if (exc is OperationCanceledException)
                    return Problem.Cancelled;
                else return Problem.Other;
            }
        }

	    public static Task<Stream> DownloadHpubFile(Uri url)
        {
            var tcs = new TaskCompletionSource<Stream>();
            hpubDownloader = new WebClient();
            hpubDownloader.AllowReadStreamBuffering = false;
            hpubDownloader.OpenReadCompleted += (s, e) =>
            {
                if (e.Cancelled) tcs.TrySetCanceled();
                else if (e.Error != null) tcs.TrySetException(e.Error);
                else tcs.TrySetResult(e.Result);
            };
            hpubDownloader.DownloadProgressChanged += (s, e) =>
            {
                int value = e.ProgressPercentage;
             labelProgress.COntent=value;//show progress text of download as %
            };
            hpubDownloader.OpenReadAsync(url);
            return tcs.Task;
        }

		private void btnCancel_Click(object sender,EventArgs e)
        {
			if (hpubDownloader.IsBusy)
			{
				hpubDownloader.CancelAsync();
				if (this.cts != null)
					this.cts.Cancel();
			}
			else if (UnzipBook != null && UnzipBook.IsBusy)
			{
				UnzipBook.CancelAsync();
			}
        }