C#

<br />
RunInBackgroundWithProgressDialog(delegate(){<br />
  // open up a progress dialog with a cancel button<br />
  // do stuff that takes a long time here.<br />
});

using System;
using System.Collections.Generic;
using System.Text;
using System.ComponentModel;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        { 
            BackgroundWorker w = new BackgroundWorker();

            w.DoWork += delegate(object o, DoWorkEventArgs e)
            {
                Console.WriteLine("sleeping 1000");
                System.Threading.Thread.Sleep(1000);
                throw new Exception("thrown");
            };

            w.RunWorkerCompleted += delegate(object o, RunWorkerCompletedEventArgs e)
            {
                if (e.Error != null)
                {
                    Console.WriteLine("should be handled here, but isn't");
                }
            };
            w.RunWorkerAsync();
            Console.Read();
        }
    }
}

<br />
 public class RichTextBoxPrintCtrl : RichTextBox<br />
    {<br />
<br />
        //Convert the unit used by the .NET framework (1/100 inch) <br />
<br />
        //and the unit used by Win32 API calls (twips 1/1440 inch)<br />
<br />
        private const double anInch = 14.4;<br />
<br />
        [StructLayout(LayoutKind.Sequential)]<br />
<br />
        private struct RECT<br />
        {<br />
<br />
            public int Left;<br />
<br />
            public int Top;<br />
<br />
            public int Right;<br />
<br />
            public int Bottom;<br />
<br />
        }<br />
<br />
        [StructLayout(LayoutKind.Sequential)]<br />
<br />
        private struct CHARRANGE<br />
        {<br />
<br />
            public int cpMin; //First character of range (0 for start of doc)<br />
<br />
            public int cpMax; //Last character of range (-1 for end of doc)<br />
<br />
        }<br />
<br />
        [StructLayout(LayoutKind.Sequential)]<br />
<br />
        private struct FORMATRANGE<br />
        {<br />
<br />
            public IntPtr hdc; //Actual DC to draw on<br />
<br />
            public IntPtr hdcTarget; //Target DC for determining text formatting<br />
<br />
            public RECT rc; //Region of the DC to draw to (in twips)<br />
<br />
            public RECT rcPage; //Region of the whole DC (page size) (in twips)<br />
<br />
            public CHARRANGE chrg; //Range of text to draw (see earlier declaration)<br />
<br />
        }<br />
<br />
        private const int WM_USER = 0x0400;<br />
<br />
        private const int EM_FORMATRANGE = WM_USER + 57;<br />
<br />
        [DllImport("USER32.dll")]<br />
<br />
        private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);<br />
<br />
        // Render the contents of the RichTextBox for printing<br />
<br />
        // Return the last character printed + 1 (printing start from this point for next page)<br />
<br />
        public int Print(int charFrom, int charTo, Graphics gr, Rectangle bounds)<br />
        {<br />
<br />
            //Calculate the area to render and print<br />
<br />
            RECT rectToPrint;<br />
<br />
            rectToPrint.Top = 0;// (int)(bounds.Top * anInch);<br />
<br />
            rectToPrint.Bottom = (int)(bounds.Height * anInch);// (int)(bounds.Bottom * anInch);<br />
<br />
            rectToPrint.Left = 0;// (int)(bounds.Left * anInch);<br />
<br />
            rectToPrint.Right = (int)(bounds.Width * anInch);// (int)(bounds.Right * anInch);<br />
<br />
            //Calculate the size of the page<br />
<br />
            RECT rectPage;<br />
<br />
            rectPage.Top = 0;//(int)(bounds.Top * anInch);<br />
<br />
            rectPage.Bottom = (int)(gr.ClipBounds.Height * anInch);//(int)(bounds.Bottom * anInch);<br />
<br />
            rectPage.Left = 0;//(int)(bounds.Left * anInch);<br />
<br />
            rectPage.Right = (int)(gr.ClipBounds.Right * anInch);//(int)(bounds.Right * anInch);<br />
<br />
            IntPtr hdc = gr.GetHdc();<br />
<br />
            FORMATRANGE fmtRange;<br />
<br />
            fmtRange.chrg.cpMax = charTo; //Indicate character from to character to <br />
<br />
            fmtRange.chrg.cpMin = charFrom;<br />
<br />
            fmtRange.hdc = hdc; //Use the same DC for measuring and rendering<br />
<br />
            fmtRange.hdcTarget = hdc; //Point at printer hDC<br />
<br />
            fmtRange.rc = rectToPrint; //Indicate the area on page to print<br />
<br />
            fmtRange.rcPage = rectPage; //Indicate size of page<br />
<br />
            IntPtr res = IntPtr.Zero;<br />
<br />
            IntPtr wparam = IntPtr.Zero;<br />
<br />
            wparam = new IntPtr(1);<br />
<br />
            //Get the pointer to the FORMATRANGE structure in memory<br />
<br />
            IntPtr lparam = IntPtr.Zero;<br />
<br />
            lparam = Marshal.AllocCoTaskMem(Marshal.SizeOf(fmtRange));<br />
<br />
            Marshal.StructureToPtr(fmtRange, lparam, false);<br />
<br />
            //Send the rendered data for printing <br />
<br />
            res = SendMessage(Handle, EM_FORMATRANGE, wparam, lparam);<br />
<br />
            //Free the block of memory allocated<br />
<br />
            Marshal.FreeCoTaskMem(lparam);<br />
<br />
            //Release the device context handle obtained by a previous call<br />
<br />
            gr.ReleaseHdc(hdc);<br />
<br />
            //Return last + 1 character printer<br />
<br />
            return res.ToInt32();<br />
<br />
        }<br />
<br />
    }<br />
<br />