How to cancel Task await after a timeout period

Question

I am using this method to instantiate a web browser programmatically, navigate to a url and return a result when the document has completed.

How would I be able to s

Answer 1

I suspect running a processing loop on another thread will not work out well, since WebBrowser is a UI component that hosts an ActiveX control.

When you're writing TAP over EAP wrappers, I recommend using extension methods to keep the code clean:

public static Task NavigateAsync(this WebBrowser @this, string url)
{
  var tcs = new TaskCompletionSource();
  WebBrowserDocumentCompletedEventHandler subscription = null;
  subscription = (_, args) =>
  {
    @this.DocumentCompleted -= subscription;
    tcs.TrySetResult(args.Url.ToString());
  };
  @this.DocumentCompleted += subscription;
  @this.Navigate(url);
  return tcs.Task;
}

Now your code can easily apply a timeout:

async Task GetUrlAsync(string url)
{
  using (var wb = new WebBrowser())
  {
    var navigate = wb.NavigateAsync(url);
    var timeout = Task.Delay(TimeSpan.FromSeconds(5));
    var completed = await Task.WhenAny(navigate, timeout);
    if (completed == navigate)
      return await navigate;
    return null;
  }
}

which can be consumed as such:

private async Task GetFinalUrlAsync(PortalMerchant portalMerchant)
{
  SetBrowserFeatureControl();
  if (string.IsNullOrEmpty(portalMerchant.Url))
    return null;
  var result = await GetUrlAsync(portalMerchant.Url);
  if (!String.IsNullOrEmpty(result))
    return new Uri(result);
  throw new Exception("Parsing Failed");
}