Question

I am creating an application that does screen shots of websites using the following method http://pietschsoft.com/post/2008/07/C-Generate-WebPage-Thumbmail-Screenshot-Image.aspx

I tried to make the application multithreaded but I have run into the following error:

[ActiveX control ‘8856f961-340a-11d0-a96b-00c04fd705a2’ cannot be instantiated because the current thread is not in a single-threaded apartment.]

Any suggestions how to fix this issue? My code is basically as follows:

List<string> lststrWebSites = new List<string>();
lststrWebSites.Add("http://stackoverflow.com");
lststrWebSites.Add("http://www.cnn.com");
foreach (string strWebSite in lststrWebSites)
{
  System.Threading.ThreadStart objThreadStart = delegate
  {
    Bitmap bmpScreen = GenerateScreenshot(strWebSite, -1, -1);
    bmpScreen.Save(@"C:\" + strWebSite + ".png", 
      System.Drawing.Imaging.ImageFormat.Png);
  };
  new System.Threading.Thread(objThreadStart).Start();
}

The GenerateScreenShot() function implementation is copied from the above URL:

public Bitmap GenerateScreenshot(string url)
{
  // This method gets a screenshot of the webpage
  // rendered at its full size (height and width)
  return GenerateScreenshot(url, -1, -1);
}

public Bitmap GenerateScreenshot(string url, int width, int height)
{
  // Load the webpage into a WebBrowser control
  WebBrowser wb = new WebBrowser();
  wb.ScrollBarsEnabled = false;
  wb.ScriptErrorsSuppressed = true;
  wb.Navigate(url);
  while (wb.ReadyState != WebBrowserReadyState.Complete) 
    { Application.DoEvents(); }


  // Set the size of the WebBrowser control
  wb.Width = width;
  wb.Height = height;

  if (width == -1)
  {
    // Take Screenshot of the web pages full width
    wb.Width = wb.Document.Body.ScrollRectangle.Width;
  }

  if (height == -1)
  {
    // Take Screenshot of the web pages full height
    wb.Height = wb.Document.Body.ScrollRectangle.Height;
  }

  // Get a Bitmap representation of the webpage as it's rendered in 
  // the WebBrowser control
  Bitmap bitmap = new Bitmap(wb.Width, wb.Height);
  wb.DrawToBitmap(bitmap, new Rectangle(0, 0, wb.Width, wb.Height));
  wb.Dispose();

  return bitmap;
} 

Answer 1

Try setting the ApartmentState of the thread hosting the browser control:

var thread = new Thread(objThreadStart);
thread.SetApartmentState(ApartmentState.STA);
thread.Start();