C# DownloadSync event not fired

Question

Experimenting with WebClient.DownloadFileAsync:

public void DownloadFile(string fileUrl, string localFile)
{
    using (WebClient client = new WebClient())
    {
        downloadingFile = true;
        client.DownloadFileCompleted += client_DownloadFileCompleted;
        client.DownloadFileAsync(new Uri(fileUrl), localFile);

        while (downloadingFile) { };
    }
}

private void client_DownloadFileCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
{
    downloadingFile = false;
}

Problem is that the DownloadFileCompleted event is never fired, so I never set downloadingFile = false => the while loop never finishes.

Any ideas for what is going wrong?

Thanks!

May be [DownloadFileCompleted needs to return the event handler.](http://stackoverflow.com/a/13920913/3796048) answers you — Mohit S, Jan 14 '16 at 04:35

score 1 · Answer 1 · answered Jan 14 '16 at 05:49

1

This seems to be a logical mistake (kind of deadlock situation) because your main thread is on continuous loop over a condition and never gets time to raise event even if the download is completed.

Solution#1: Remove the while (downloadingFile) { }; line to release the main thread, if you want to hold the control flow you can make your method DownloadFile async and use following line of code to awaitable varient of DownloadFile method.

await client.DownloadFileTaskAsync(new Uri(fileUrl), localFile);

answered Jan 14 '16 at 05:49

Asad Mehmood

135
8

Agree, I'm also thinking it's some kind of deadlock. DownloadFileTaskAsync is a void, so await can't be used. – Louisa Jan 14 '16 at 07:32
DownloadFileAsync is void but DownloadFileTaskAsync returns Task which is awaitable – Asad Mehmood Jan 14 '16 at 09:57

score 0 · Answer 2 · answered Jan 14 '16 at 05:39

0

You have to return an instance of type AsyncCompletedEventHandler from your eventhandler (Client_DownloadFileCompleted) and not void.

See MSDN link for more details.

answered Jan 14 '16 at 05:39

Martin

644
5
11

C# DownloadSync event not fired

2 Answers2