Question

I have this piece of code in my Windows Store app where I handle a button click. But somehow, UI freezes when I click this button on rare occasion. It mostly happens when I connect to a Wi-Fi network further away than the one I usually connect to. Taking into consideration that I download a RSS feed from the internet, it is most probably related to my using of async/await keywords. If I correctly understood the mechanics of async/await, UI thread should not block at all. Am I missing something here?

    private async void Add_Click(object sender, RoutedEventArgs e)
    {
        AddButton.Visibility = Windows.UI.Xaml.Visibility.Collapsed;
        DownloadProgressRing.Visibility = Windows.UI.Xaml.Visibility.Visible;
        DownloadProgressRing.IsActive = true;

        RssData rssData = App.Current.Resources["rssData"] as RssData;
        Uri uri = FixUrl(RssUrl.Text);

        if (uri != null)
        {
            newRssFeed = new RssFeed(uri.ToString());
            Task<bool> success = newRssFeed.RetrieveFeed();
            if (await success)
            {
                SubmitButtonPanel.Visibility = Windows.UI.Xaml.Visibility.Visible;
                FeedTitleTextBox.Text = newRssFeed.Title == null ? String.Empty : newRssFeed.Title;
            }
        }
    }

Constructor for RssFeed:

    public RssFeed(string url)
    {
        Url = url; 
    }

RetrieveFeed function:

    public async Task<bool> RetrieveFeed()
    {
        if (Url != null)
        {
            try
            {
                SyndicationClient sc = new SyndicationClient();
                SyndicationFeed sf = await sc.RetrieveFeedAsync(new Uri(Url, UriKind.Absolute));
                if (sf != null)
                {
                    ValidateAndInitFeed(sf);
                    return true;
                }
            }
            catch (Exception ex)
            {
            }
        }

        return false;
    }

    private void ValidateAndInitFeed(SyndicationFeed feed)
    {
        if (feed.Title != null)
            Title = feed.Title.Text;
        if (feed.ImageUri != null)
            Image = feed.ImageUri.ToString();
        if (feed.Subtitle != null)
            Subtitle = feed.Subtitle.Text;
    }

Answer 1

Try calling RetrieveFeed() on a background thread. Perhaps processing the request or response is what takes a lot of time and if it is started on UI thread – it will run on UI thread.

Task<bool> success = null;
await Task.Run(
    () => success = newRssFeed.RetrieveFeed());