How to deal with exceptions when using WebClient.DownloadFileAsync

Question

I am downloading some files from the internet using a WebClient in the following way:

try  
{
   ManualResetEvent mr = new ManualResetEvent(fals         


        

Answer 1

What you can do is create a Task (an async operation) and use the ContinueWith directive to handle the exception. This can be a bit unreadable

using (WebClient wc = new WebClient())
{
    wc.DownloadFileCompleted += ((sender, args) =>
    {
        if (args.Error == null)
        {
            File.Move(filePath, Path.ChangeExtension(filePath, ".jpg"));
            mr.Set();
        }
        else
        {
            //how to pass args.Error?
        }
    });
    Task.Factory.StartNew(() => wc.DownloadFile(
                                 new Uri(string.Format("{0}/{1}",
                                 Settings1.Default.WebPhotosLocation,
                                 Path.GetFileName(f.FullName))), filePath))
                .ContinueWith(t => Console.WriteLine(t.Exception.Message));
}

However, with the introduction of .NET 4.5, Webclient exposes a task based async download for you!

using (WebClient wc = new WebClient())
{
    wc.DownloadFileCompleted += ((sender, args) =>
    {
        if (args.Error == null)
        {
            File.Move(filePath, Path.ChangeExtension(filePath, ".jpg"));
            mr.Set();
        }
        else
        {
            //how to pass args.Error?
        }
    });
    wc.DownloadFileTaskAsync(new Uri(string.Format("{0}/{1}",
                                 Settings1.Default.WebPhotosLocation,
                                 Path.GetFileName(f.FullName))),
                                 filePath)
      .ContinueWith(t => t.Exception.Message)
}