Web Services are an integral part of the .NET framework that provide a cross-platform solution for exchanging data between distributed systems. Although Web Services are normally used to allow different operating systems, object models and programming languages to send and receive data, they can also be used to dynamically inject data into an ASP.NET AJAX page or send data from a page to a back-end system. All of this can be done without resorting to postback operations.While the ASP.NET AJAX UpdatePanel control provides a simple way to AJAX enable any ASP.NET page, there may be times when you need to dynamically access data on the server without using an UpdatePanel. In this article you'll see how to accomplish this by creating and consuming Web Services within ASP.NET AJAX pages. This article will focus on functionality available in the core ASP.NET AJAX Extensions as well as a Web Service enabled control in the ASP.NET AJAX Toolkit called the AutoCompleteExtender. Topics covered include defining AJAX-enabled Web Services, creating client proxies and calling Web Services with JavaScript. You'll also see how Web Service calls can be made directly to ASP.NET page methods.

Web Services Configuration

<httpHandlers>
<remove verb="*" path="*.asmx"/>
<add verb="*" path="*.asmx" validate="false"           type="System.Web.Script.Services.ScriptHandlerFactory,           System.Web.Extensions, Version=1.0.61025.0, Culture=neutral,           PublicKeyToken=31bf3856ad364e35">
<authenticationService enabled="true" />
</httpHandlers>

In the next section you'll see how to create Web Services capable of handling JSON request messages and responding with both simple and complex types.

The ASP.NET AJAX framework provides several different ways to call Web Services. You can use the AutoCompleteExtender control (available in the ASP.NET AJAX Toolkit) or JavaScript. However, before calling a service you have to AJAX-enable it so that it can be called by client-script code. Whether or not you're new to ASP.NET Web Services, you'll find it straightforward to create and AJAX-enable services. The .NET framework has supported the creation of ASP.NET Web Services since its initial release in 2002 and the ASP.NET AJAX Extensions provide additional AJAX functionality that builds upon the .NET framework's default set of features. Visual Studio .NET 2008 Beta 2 has built-in support for creating .asmx Web Service files and automatically derives associated code beside classes from the System.Web.Services.WebService class. As you add methods into the class you must apply the WebMethod attribute in order for them to be called by Web Service consumers.

[WebMethod] public Customer[] GetCustomersByCountry(string country)
{
      return Biz.BAL.GetCustomersByCountry(country);
}

[System.Web.Script.Services.ScriptService]
[WebService(Namespace = "http://xmlforasp.net")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
public class CustomersService : System.Web.Services.WebService
{
      [WebMethod]  
     public Customer[] GetCustomersByCountry(string country)
      {  
          return Biz.BAL.GetCustomersByCountry(country);
     }
}