Asynchronous Calls to Web Services

<%@ WebService language="C#" class="Calculator" %>

using System;

using System.Web.Services;

using System.Xml.Serialization;

public class Calculator {

    [WebMethod]

    public int Add(int a, int b)

    {

        return a + b;

    }

    [WebMethod]

    public int Subtract(int a, int b)

    {

        return a - b;

    }

    [WebMethod]

    public int Multiply(int a, int b)

    {

        return a * b;

    }

    [WebMethod]

    public int Divide(int a, int b)

    {

        return a/b;

    }

}

Imports Test.Calculator

Public Class Form2

    Inherits System.Windows.Forms.Form

    'CallBack object is initialized with the

    'reference of the Delegate method

    Dim oCB As New AsyncCallback(AddressOf CallBack)

    ' Proxy of the calculator web service.

    Dim oCalc As Calculator.Calculator

    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        oCalc = New Calculator.Calculator

        MessageBox.Show("Form is loaded")

        'The call to the Web Service is given.

        oCalc.BeginAdd(5, 10, oCB, Nothing)

        'Further Processing continues till the web service responds

        MessageBox.Show("Calculator.BeginAdd is called")

    End Sub

    'The Delegate method which receives the response from

    'the web service

    Private Sub CallBack(ByVal Result As IAsyncResult)

        Dim iRes As Integer

        iRes = oCalc.EndAdd(Result)

        MessageBox.Show(iRes.ToString())

    End Sub

End Class