AsyncPatternsWPF.MainWindow.OnAsyncEventPattern C# (CSharp) Method

        private void OnAsyncEventPattern(object sender, RoutedEventArgs e)
        {
            foreach (var req in GetSearchRequests())
            {
                var client = new WebClient();
                foreach (var header in req.Headers)
                {
                    client.Headers.Add(header.Key, header.Value);
                }
                client.Credentials = req.Credentials;
                client.DownloadStringCompleted += (sender1, e1) =>
                {
                    try
                    {
                        string resp = e1.Result;
                        var images = req.Parse(resp);
                        foreach (var image in images)
                        {
                            _searchInfo.List.Add(image);
                        }
                    }
                    catch (Exception ex) when (ex.InnerException?.Message.Contains("401") ?? false)
                    {
                        MessageBox.Show(errorMessage, "Registration Needed");
                    }
                };
                client.DownloadStringAsync(new Uri(req.Url));
            }
        }