i send an event through a button on an aspx page to a statemachine workflow
and then let the workflow to use CallExternalMethod to raise a local service
event which  is booked by a asp.net host method, the method is to change a
Label control's Text property to a new string.

here is my code for Local Service:
=======
namespace myService
{

   //host -> wf  Define the Interface
   [ExternalDataExchange]
   public interface IService
   {
       event EventHandler<myargs> event_from_host_to_wf;
       void method_from_wf_to_host();
   }

   //myargs derived from ExternalDataEventArgs
   [Serializable]
   public class myargs : ExternalDataEventArgs
   {
       private String _msg;
       public myargs(Guid instanceID, string msg)
           : base(instanceID)
       {
           _msg = msg;
       }

       public String Msg
       {
           get { return _msg; }
           set { _msg = value; }
       }

   }

   
   //host <-> wf
   public class myServiceClass:IService
   {
       #region IService Members

       public event EventHandler<myargs> event_from_host_to_wf;

       public void method_from_wf_to_host()
       {
           //throw new NotImplementedException();
           event_from_wf_to_host();
           
       }

       #endregion

       #region Host Members
       public void raise_event_from_host_to_wf(Guid instanceId, string msg)
       {//prepare myargs
           myargs e = new myargs(instanceId, msg);
           event_from_host_to_wf(null, e);
       }

       public delegate void delegate_event_from_wf_to_host();
       public event delegate_event_from_wf_to_host event_from_wf_to_host;
       
       #endregion
   }
}

===================
Here is the behind code for page1.aspx
namespace SimpleChangeWebUI
{
   public partial class _Default : System.Web.UI.Page
   {

       private WorkflowRuntime _runtime;
       private ManualWorkflowSchedulerService _scheduler;
       private ExternalDataExchangeService _exchangeService;
       private myServiceClass _myServiceClass;
       private bool operation_from_wf_is_recorded = false;
       private ManualResetEvent _waitHandle = new ManualResetEvent(false);

       protected void Page_Load(object sender, EventArgs e)
       {
           btn_create_a_wf_instance.Enabled = true;
           btn_change_UI_through_wf_instance.Enabled = false;

           _runtime = Application["runtime"] as WorkflowRuntime;
           _scheduler =
_runtime.GetService<ManualWorkflowSchedulerService>();
           _exchangeService =
_runtime.GetService<ExternalDataExchangeService>();
           _myServiceClass =
_exchangeService.GetService(typeof(myServiceClass)) as myServiceClass;
       }

       protected void btn_create_a_wf_instance_Click(object sender,
EventArgs e)
       {
           btn_create_a_wf_instance.Enabled = false;
           btn_change_UI_through_wf_instance.Enabled = true;
           Label1.Text = "a workflow instance has been created!";

           _myServiceClass.event_from_wf_to_host += new
myServiceClass.delegate_event_from_wf_to_host(change_web_UI);

           WorkflowInstance _instance =
_runtime.CreateWorkflow(typeof(Workflow1));
           Session.Add("instanceId", _instance.InstanceId);
           _instance.Start();
           _scheduler.RunWorkflow(_instance.InstanceId);

       }

       protected void btn_change_UI_through_wf_instance_Click(object
sender, EventArgs e)
       {
           Guid _instanceID = (Guid)Session["instanceId"];
           _myServiceClass.raise_event_from_host_to_wf(_instanceID,
"nothing!");//host 向 wf 发出 event!
           _scheduler.RunWorkflow(_instanceID);
           _waitHandle.WaitOne();
       }

       private void change_web_UI()
       {
           Label1.Text = "the Label.Text has been modified through the
workflow instance";
        }
   }
}

=============
I set breakpoints and find that the change_web_UI() function has been
undoubtly executed, but disappointingly, the Label.Text remains the same.
Could anyone tell me why? Is this because the page is rendered before the
workflow completed?
but I DO have used the ManualWorkflowSchedulerService in my
WorkflowRuntime...

Any suggestion will be deeply appreciated!
my email is : smwikipedia@gmail.com
wish somebody would contact me and shed some light on me...  :(