Update UI ASP.NET Control - Asynchronous (CallBack Approach) - Calling WebService Methods - asp.net

Question

Here is the sample code for WebService written in ASP.NET 1.1 using VB.NET:
<System.Web.Services.WebService(Namespace := "http://tempuri.org/WebService_Simple/Service1")> _
Public Class Service1
Inherits System.Web.Services.WebService
<WebMethod()> _
Public Function Add(ByVal A As Integer, ByVal B As Integer) As Integer
System.Threading.Thread.Sleep(2000)
Return A + B
End Function
End Class
Here is the Client code:
Public Class WebForm1
Inherits System.Web.UI.Page
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim proxy As New Service1
Dim ac As New AsyncCallback(AddressOf MyCallback)
Dim ar As IAsyncResult = proxy.BeginAdd(10, 20, ac, proxy)
System.Threading.Thread.Sleep(1000)
End Sub
Public Sub MyCallback(ByVal ar As IAsyncResult)
Dim proxy As Service1 = CType(ar.AsyncState, Service1)
Dim result As Integer = proxy.EndAdd(ar)
Label1.Text = "Result = " & result.ToString()
End Sub
End Class
I am using Visual Studio.NET 2003 (ASP.NET 1.1 / VB.NET). I am getting the right values into "result" variable. But it is NOT updating the UI element (Label1). I know the reason. Because UI - MAIN - thread is different than the one which is using CALLBACK - WORKER - thread. Can you provide me sample code so that it will update the UI (Label1) control using VB.NET in Visual Studio.NET 2003 ?
Thanks

Answer 1

This is the answer. It is negative but it is answer. You can't and shouldn't do this in ASP.NET Web Forms because Page cycle moves through well known set of steps. There shouldn't be any async/multi-threaded programming done in page cycle methods. and you definitely shouldn't make ASP.net thread sleeping.
Your Button1_Click is part of the cycle and when it executes, ASP.net framework already executes something else. And whatever you call asynchronously is just left behind. The code executes but values never affect anything.
If you trying to achieve asynchronous behavior in ASP.net web forms, you need to include some client-side devices that will call your web service. I am not even sure now that the old framework you use has something like update panel or there is AJAX toolkit for it. Bu that is how you need to achieve it without page reloading - you use jQuery or something else to call your web service. What you tried to do in your example is a dead end.
And seriously, start using new frameworks. At least 3.5.