A simple implemention for calling asych methods from the UI

Examples

1.

dispatcher.ExecuteOnMainUIThread(CommandManager.InvalidateRequerySuggested);

2.

dispatcher.Execute(() =>
                                        {
                                           SomeLongRunningMethodHere();
                                        });

The interface

using System;

namespace Mvvm
{
    public interface IDispatcher
    {
        void Execute(Action action);

        void ExecuteOnMainUIThread(Action action);
    }
}

Synchronous for use in Testing

using System;

namespace Mvvm
{
    public class SynchronousDispatcher : IDispatcher
    {               
       public void Execute(Action action)
        {
            action();
        }
        
        public void ExecuteOnMainUIThread(Action action)
        {
            action();
        }
    }

}

Asynchronous for use by the application at run time

using System;

namespace Mvvm 
{
    using System.Windows;
    using System.Windows.Threading;

    public class AsynchronousDispatcher : IDispatcher
    {
        public void Execute(Action action)
        {
            action.BeginInvoke(CallBack, action);
        }        

        public void ExecuteOnMainUIThread(Action action)
        {
            Dispatcher dispatcher;

            if (Application.Current != null)
            {
                dispatcher =  Application.Current.Dispatcher;
            }
            else
            {
                dispatcher = Dispatcher.CurrentDispatcher;
            }

            dispatcher.Invoke(action);
        }

        private void CallBack(IAsyncResult result)
        {
            try
            {
                ((Action)result.AsyncState).EndInvoke(result);            
            }
            catch (Exception ex)
            {
                // Need to raise the exception on the main thread
                ExecuteOnMainUIThread(() =>
                                          {
                                              throw ex;
                                          }
                    );
            }
            finally
            {
                result.AsyncWaitHandle.Close();    
            }
            
            
        }
    }
}

ThreadPool.QueueUserWorkItem(new WaitCallback(LoadUsers));

private void LoadUsers(Object stateInfo)

    var site = new SPSite(testHarnessSettings.Url);

     var web = site.OpenWeb();

      foreach(SPUser user in web.AllUsers)

      {

       if (usersListBox.InvokeRequired)

       {

             usersListBox.Invoke(new MethodInvoker(delegate { usersListBox.Items.Add((user.LoginName)); }));

       }                                

http://weblogs.asp.net/justin_rogers/articles/126345.aspx