Harvesting information from the Internet asynchronously

Question

I have a WPF application which presents a list of items. I would like to show an icon in UI if certain information exists on a web server for a given item (I need to download HTML web-page and verify its content to decide if the icon should be shown or not).

The number of items may be quite big (more than 100), so requesting a web server synchronously may freeze the application for a longer time. I would like to do it asynchronously and update the UI after retrieving each piece of information. What is the best way to deal with this issue.

Answer 1

Hi,

Using Backgroundworkers is a good way to solve your problem It's easy to use : You run an asyn operation without freeze your app and you are notified when operation asyn is done.

Some exemple here : http://msdn.microsoft.com/en-us/magazine/cc163328.aspx http://channel9.msdn.com/forums/TechOff/252416-C-and-WPF-progressbar/

MSDN definition of BW : http://msdn.microsoft.com/en-us/library/8xs8549b.aspx

hope this help.

Answer 2

Use a BackgroundWorker to do the work. Update the UI in the ProgressChanged event handler

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    WebClient wc = new WebClient();
    int count = urlsToCheck.Count;
    for(int i = 0; i < count; i++)
    {
        bool urlValid = CheckUrl(url);
        backgroundWorker1.ReportProgress(100 * (i + 1) / count, new CheckUrlResult(url, urlValid));
    }
}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    CheckUrlResult result = e.UserState as CheckUrlResult;
    textBox1.Text += string.Format("{0} : {1}\n", result.Url, result.IsValid);
    progressBar1.Value = e.ProgressPercentage;
}