How to: Make an Asynchronous Call from a Web Service Client

Article
05/12/2009

This topic is specific to a legacy technology. XML Web services and XML Web service clients should now be created using Windows Communication Foundation (WCF).

The following code example demonstrates how to make an asynchronous call to a Web service from a client application. This example illustrates one of the guidelines explained in the topic, Design Guidelines for XML Web Services Created Using ASP.NET.

Security Note:
This example has a text box that accepts user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. For more information, see Script Exploits Overview.

Example

<%@ Page Language="C#" %>
<%@ Import Namespace="System.Net" %>
<html>
   <script language="C#" runat="server">
      void EnterBtn_Click(Object Src, EventArgs E) 
      {
         MyMath.Math math = new MyMath.Math();
         // Call to Add Web service method asynchronously 
         // and then wait for it to complete.
         IAsyncResult result =
                         math.BeginAdd(Convert.ToInt32(Num1.Text),
                                       Convert.ToInt32(Num2.Text),
                                       null,
                                       null);
         // Wait for asynchronous call to complete.
         result.AsyncWaitHandle.WaitOne();
         // Complete the asynchronous call to Add Web service method.
         float total = math.EndAdd(result);
         // Display results in a Label control.
         Total.Text = "Total: " + total.ToString();
      }
   </script>
<body>
   <form action="MathClient.aspx" runat=server>
      <font face="Verdana"> 
         Enter the two numbers you want to add and then press 
         the Total button.
         <p>
         Number 1: 
         <asp:textbox id="Num1" 
         runat=server/>  
         +
         Number 2: 
         <asp:textbox id="Num2" 
              runat=server/> 
         =
         <asp:button id="Total_Button"
              text="Total" 
              OnClick="EnterBtn_Click" 
              runat=server/>
         <p>
         <asp:label id="Total" runat=server/>
      </font>
    </form>
</body>
</html>

<%@ Page Language="VB" %>
<%@ Import Namespace="System.Net" %>
<html>
   <script language="VB" runat="server">
      Sub EnterBtn_Click(Src As Object, E As EventArgs) 
         Dim math As New MyMath.Math()
         ' Call to Add Web service method asynchronously 
         ' and then wait for it to complete.
         Dim result As IAsyncResult = _
                         math.BeginAdd(Convert.ToInt32(Num1.Text), _
                                       Convert.ToInt32(Num2.Text), _
                                       Nothing, _
                                       Nothing)
               
         ' Wait for asynchronous call to complete.
         result.AsyncWaitHandle.WaitOne()
         ' Complete the asynchronous call to Add Web service method.
         Dim addtotal As Single = math.EndAdd(result)
         ' Display results in a Label control.
         Total.Text = "Total: " & addtotal.ToString()
      End Sub
   </script>
<body>
   <form action="MathClient.aspx" runat=server>
      <font face="Verdana"> 
         Enter the two numbers you want to add and then press 
         the Total button.
         <p>
         Number 1: 
         <asp:textbox id="Num1" 
         runat=server/>  
         +
         Number 2: 
         <asp:textbox id="Num2" 
              runat=server/> 
         =
         <asp:button id="Total_Button"
              text="Total" 
              OnClick="EnterBtn_Click" 
              runat=server/>
         <p>
         <asp:label id="Total" runat=server/>
      </font>
    </form>
</body>
</html>

How to: Make an Asynchronous Call from a Web Service Client

Example

See Also

Tasks

Other Resources

Additional resources