Question

I’m working on silverlight rss reader as schoolproject and I have one problem.
I want to define list of feed sources in xml and load this xml to list of button, each button for one feed.
xml looks like

<FeedList>  
  <Feed ButtonContent="HDRip's on RlsLog.net" Url="http://www.rlslog.net/category/movies/hdrip/feed/" />
</FeedList>

I’m loading this xml using linq and creating button

XDocument xdoc = XDocument.Load(string.Format("feeds.xml"));

if (xdoc != null)
{                 
    var feedlist =
        (from l in xdoc.Descendants("Feed")
            select new MyButtons
            {
                 Content = l.Attribute("ButtonContent").Value,
                 FeedUrl = l.Attribute("Url").Value
            }
        ).ToList();

    foreach (MyButtons feedbutton in feedlist)
    {
        Button b1 = new Button();
        b1.Content = feedbutton.Content;
        b1.Click += (s, e) => { feedViewer.LoadFeed(feedbutton.FeedUrl); };
        ButtonPanel.Children.Add(b1);
    }
}

button content is loading fine but that feed url is used the last one in xml for all buttons. could you please advice me what i’m doing wrong?

Answer 1

It looks like feedbutton is being captured as an iteration variable, thus causing the behavior you’re describing when you assign the event handler with the lambda expression.

Try this instead:

MyButtons tempButton = feedbutton;
b1.Click += (s, e) => { feedViewer.LoadFeed(tempButton.FeedUrl); };

Eric Lippert has blogged about this topic:

• Closing over the loop variable considered harmful
• Closing over the loop variable, part two