Draw image on a form from a separate thread

Question

I am currently working on a Windows.Forms application. It's basically a simple motion detection problem.

I have a button on a form, that when pressed launches a background worker that does the following :

1. Fetch an image from disk
2. Create a new bitmap, to be used as the buffer.
3. Perform Motion Detection
4. From the results of Motion Detection, update the buffer (using the buffer's drawing surface)
5. Fire the Progress Changed Event with an argument consisting of a clone of the buffer, basically (sender as BackgroundWorker).ReportProgress((Bitmap)buffer.Clone())

In the Progress Changed Event, I then draw the buffer to screen.

if (!PnlImage.IsDisposed)
            PnlImage.CreateGraphics().DrawImageUnscaled(buffer, 0, 0);

I can't help wondering if this is the best way to draw the updated image on the screen. Can anyone suggest any improvements I can make? Thanks.

EDIT : I have since updated the program to use the .NET Framework 4, and we're no longer using a BackgroundWorker. Instead, we are now using the System.Threading.Tasks namespaces, and using Invoke to update the background image from within the task.

Thanks to all replies.

Answer 1

I believe the root of any problems you may be experiencing is the fact that any GUI updates must be done on the UI thread. You cannot safely update the UI from another thread. So, basically, you need to do something like the following (I'm just changing the background color as an example, but you can do whatever you like):

    private void SomethingCalledFromBackgroundThread()
    {
        panel1.Invoke(new DoUpdatePanel(UpdatePanel), Color.Blue);
    }

    private delegate void DoUpdatePanel(Color aColor);

    private void UpdatePanel(Color aColor)
    {
        panel1.BackColor = aColor;
    }

============ Update =======>

@Ash you have mischaracterized my answer. I did not say to call Invoke from within ProgressChanged. @Jean keep in mind that ReportProgress/ProgressChanged is being run asynchronously--which is why you find yourself making a clone of your image. This would not be necessary if you use Invoke from within your background thread, rather than ReportProgress.