Question

I’m trying to make a progressbar advance using a BackgroundWorker. The final goal is to show the progress of a background search, but I first want to get to know the progress bar by doing a simple simulation. This is the code:

    public MainWindow()
    {
        InitializeComponent();

        worker = new BackgroundWorker(); // variable declared in the class
        worker.WorkerReportsProgress = true;
        worker.DoWork += new DoWorkEventHandler(worker_DoWork);
        worker.ProgressChanged += new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged);
        worker.RunWorkerCompleted += worker_RunWorkerCompleted;
    }

    private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        this.Title += " DONE";
    }

    private void worker_DoWork(object sender, DoWorkEventArgs e)
    {
        for(int j = 0; j <= 100; j++)
        {
            worker.ReportProgress(j);
            Title += j.ToString();
            Thread.Sleep(50);
        }
    }

    void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        searchProgressBar.Value = e.ProgressPercentage;
    }

But when I run it, it skips right to the end, without altering the progressbar in any way. When I debug it step-by-step, the last step I get to is worker.ReportProgress(j);, then control returns to the program and worker_RunWorkerCompleted is called. Why?

Answer 1

In case you trying to change the UI content, you should put the calls on UI Dispatcher. You can't modify UI objects from background thread. Replace your lines with these –

App.Current.Dispatcher.Invoke((Action)delegate()
        {
            Title += j.ToString();
        });

and

App.Current.Dispatcher.Invoke((Action)delegate()
        {
            Title = "Done";
        });