Question

I have already implemented a functionnal application that parses 26 pages of html all at once to produce an xml file with data contained on the web pages. I would need to implement a thread so that this method can work in the background without causing my app to seems unresponsive.

Secondly, I have another function that is decoupled from the first one which compares two xml files to produce a third one and then transform this third xml file to produce an html page using XSLT. This would have to be on a thread, where I can click Cancel to stop the thread whithout crashing the app.

What is the easiest best way to do this using WPF forms in VS 2010 ?

I have chosen to use the BackgroundWorker.

BackgroundWorker implementation:

public partial class MainWindow : Window
    {
        private BackgroundWorker bw = new BackgroundWorker();

        public MainWindow()
        {
            InitializeComponent();
            bw.WorkerReportsProgress = true;
            bw.DoWork += new DoWorkEventHandler(bw_DoWork);
            bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted);
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            this.LoadFiles();
        }

        private void btnCompare_Click(object sender, EventArgs e)
        {
            if (bw.IsBusy != true)
            {
                progressBar2.IsIndeterminate = true;
                // Start the asynchronous operation.
                bw.RunWorkerAsync();
            }

        }

        private void bw_DoWork(object sender, DoWorkEventArgs e)
        {
            StatsProcessor proc = new StatsProcessor();
            if (lstStatsBox1.SelectedItem != null)
                if (lstStatsBox2.SelectedItem != null)
                    proc.CompareStats(lstStatsBox1.SelectedItem.ToString(), lstStatsBox2.SelectedItem.ToString());
        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            progressBar2.IsIndeterminate = false;
            progressBar2.Value = 100;
        }

I have started with the bgworker solution, but it seems that the bw_DoWork method is never called when btnCompare is clicked, I must be doing something wrong… I am new to threads.

Answer 1

If you’re new to threading I think the easiest to start with would be using a BackgroundWorker:

• It uses another thread: You can asynchronously perform the HTML parsing while your app remains responsive
• It supports cancellation: You can can cancel the XML to HTML conversion

The BackgroundWorker is event-driven so it’s much easier to get your ahead around if you’re new to multi-threading. The .NET 4 Task library is much more flexible, but a little more involved to take advantage of especially with UI updates.

Example:

BackgroundWorker worker = new BackgroundWorker();
worker.DoWork += new DoWorkEventHandler((o, args) =>
{
    //Long running stuff here       
    Thread.Sleep(10000);
    string result = "Hi UI!";
    args.Result = result;
});

worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler((o, args) =>
{
    if (args.Result != null)
    {
        SomeTextBox.Text = args.Result;
    }
});

worker.RunWorkerAsync();