Question

Im reading a WPF book and I see this code:

    private void bgw1_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        int percenti;
        percenti = e.ProgressPercentage;
        progressBar1.Value = percenti;
    }

The question is simple.
if

ProgressBar belongs to UI Thread and
BackGroundWorker works with a Background Thread

Why are there no errors (like: The calling thread cannot access this object because a different thread owns it.)?

thanks.

Answer 1

Why are there no errors (like: The calling thread cannot access this object because a different thread owns it.)?

This is one of the main advantages to using BackgroundWorker. The BackgroundWorker component automatically marshals calls for progress and completion back to the synchronization context (thread) that starts the job.

In this case, that means that the event handlers for ProgressChanged (and the completion event) happen on the WPF UI thread.