Is there a smarter way than a busy-wait to check for download completion of System.Net.WebClient.DownloadFileAsync()?

Question

I\'m downloading a file using System.Net.WebClient.DownloadFileAsync(). The only reason for using the async version is to show the progress of the download. My code executio

Answer 1

Use an AutoResetEvent. Call its Set() method in a DownloadFileCompleted event handler, its WaitOne() method after the DownloadFileAsync() call.

Answer 2

using(WebClient oWebClient = new WebClient())
{
    // use an event for waiting, rather than a Thread.Sleep() loop.
    var notifier = new AutoResetEvent(false);
    oWebClient.Encoding = System.Text.Encoding.UTF8;
    long lReceived = 0;
    long lTotal = 0;

    // Set up a delegate to watch download progress.
    oWebClient.DownloadProgressChanged += delegate(object sender, DownloadProgressChangedEventArgs e)
    {
        Console.WriteLine(e.ProgressPercentage + "% (" + e.BytesReceived / 1024f + "kb of " + e.TotalBytesToReceive / 1024f + "kb)");
        // Assign to outer variables to allow busy-wait to check.
        lReceived = e.BytesReceived;
        lTotal = e.TotalBytesToReceive;
    };

    // Set a delegate to watch for when the download is complete
      oWebClient.OpenReadCompleted += delegate(object sender, OpenReadCompletedEventArgs e)
    {
         // Indicate that things are done
         notifier.Set();
    };

    oWebClient.DownloadFileAsync(new Uri(sUrl + "?" + sPostData), sTempFile);

    // wait for signal to proceed
    notifier.WaitOne();
}

I have expanded on @OJ's answer to instead set the notifier when the OpenReadCompleted fires. This will stop the thread from hanging if the file errors during download.

Ref: WebClient DownloadFileAsync hangs

Answer 3

using(WebClient oWebClient = new WebClient())
{
    // use an event for waiting, rather than a Thread.Sleep() loop.
    var notifier = new AutoResetEvent(false);

    oWebClient.Encoding = System.Text.Encoding.UTF8;
    long lReceived = 0;
    long lTotal = 0;
    // Set up a delegate to watch download progress.
    oWebClient.DownloadProgressChanged += delegate(object sender, DownloadProgressChangedEventArgs e)
    {
        Console.WriteLine(e.ProgressPercentage + "% (" + e.BytesReceived / 1024f + "kb of " + e.TotalBytesToReceive / 1024f + "kb)");
        // Assign to outer variables to allow busy-wait to check.
        lReceived = e.BytesReceived;
        lTotal = e.TotalBytesToReceive;

        // Indicate that things are done
        if(lReceived >= lTotal) notifier.Set();
    };

    oWebClient.DownloadFileAsync(new Uri(sUrl + "?" + sPostData), sTempFile);

    // wait for signal to proceed
    notifier.WaitOne();
}