WebClient.DownloadProgressChanged never gets called

Question

I added an event handler to the WebClient\'s DownloadProgressChanged event, but it never seems to fire. The file successfully downloads, but without having its

Answer 1

client.DownloadFile(url, savepath);

You have to use the async version to download a file, currently you use the blocking, synchronous version.

From the msdn docs for WebClient.DownloadProgressChanged:

Occurs when an asynchronous download operation successfully transfers some or all of the data.

In your case that would be:

client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged);
client.DownloadFileAsync (url, savepath);

Since your method does not directly return any result, this refactoring shouldn't be a problem, note though that the download most likely has not been completed by the time the method returns to the caller.

Answer 2

If you want to use WebClient synchronously, while getting progress updates you can rely on this method detailed here

http://alexfeinberg.wordpress.com/2014/09/14/how-to-use-net-webclient-synchronously-and-still-receive-progress-updates/

public void DownloadFile(Uri uri, string desintaion)
{
  using(var wc = new WebClient())
  {
    wc.DownloadProgressChanged += HandleDownloadProgress;
    wc.DownloadFileCompleted += HandleDownloadComplete;

    var syncObject = new Object();
    lock(syncObject)
    {
       wc.DownloadFileAsync(sourceUri, destination, syncObject);
       //This would block the thread until download completes
       Monitor.Wait(syncObject);
    }
  }

  //Do more stuff after download was complete
}

public void HandleDownloadComplete(object sender, AsyncCompletedEventArgs args)
{
   lock(e.UserState)
   {  
      //releases blocked thread
      Monitor.Pulse(e.UserState);
   }
}


public void HandleDownloadProgress(object sender, DownloadProgressChangedEventArgs args)
{
  //Process progress updates here
}