C#

delegate void Result(string s);
 
delegate void ExceptionHandler(Exception ex);
  
private void MyCallback(IAsyncResult ar)
{      
    getDNS getIP = (getDNS)ar.AsyncState;      
 
    try
    {
        string result = getIP.EndInvoke(ar);
 
        BeginInvoke(new Result(MyResultMethod), result);
    } 
    catch(Exception ex) // Probably should catch a more specific Exception type.
    {
        BeginInvoke(new ExceptionHandler(MyExceptionHandler), ex);
    }
}
 
private void MyResultMethod(string s)
{
    MessageBox.Show(s);
 
    // Do other updating...
}
 
private void MyExceptionHandlerMethod(Exception ex)
{
    MessageBox.Show(ex.Message);
 
    // Other exception handling code...
}