Question

Please see the following code:

foreach(string url in urls)
{
  //Method that will process url ProcessUrl(url)
  //Add eached proccessed url to a treelist
}

ProcessUrl method have HttpWebRequest and HttpWebResponse so sometime it takes a nudge and if there were many links it will take time which will hang my program.

I can’t actually suggest a solution of think of one, because i may based it on something wrong so what i want is to make this code runs while i can operate 100% in my program without any crashes or hangs, and that each newly processed link will be inserted to the treelist without any lag.

Answer 1

If you want to perform a long-running operation in the background and pass the results of the operation back to the UI as they become available, while at the same time the UI stays responsive, then it’s straightforward to use BackgroundWorker here.

    void BeginExpensiveOperation()
    {
        var worker = new BackgroundWorker();
        worker.WorkerReportsProgress = true;
        worker.DoWork += ExpensiveWork;
        worker.ProgressChanged += WorkerOnProgressChanged;

        List<string> urls = new List<string> { "http://google.com" };
        worker.RunWorkerAsync(urls);
    }

    // runs in a worker thread
    void ExpensiveWork(object sender, DoWorkEventArgs e)
    {
        var worker = (BackgroundWorker)sender;
        var urls = (List<string>) e.Argument;
        foreach (var url in urls)
        {
            //TODO: do your work here synchronously
            var result = new WebClient().DownloadString(url);

            //TODO: pass the result in the userState argumetn of ReportProgress
            worker.ReportProgress(0, result); // will raise worker.ProgressChanged on the UI thread
        }
    }

    private void WorkerOnProgressChanged(object sender, ProgressChangedEventArgs progressChangedEventArgs)
    {
        //this executes on the UI thread
        var value = progressChangedEventArgs.UserState;
        //TODO: use result of computation to add it to the UI
        panel.Children.Add(new TextBlock {Text = value.ToString()});
    }

Fill in your problem-specific code in the //TODO: placeholders and call BeginExpensiveOperation() to start the operation asynchronously.