Programming ASP.NET AJAX

Chapter 5. Web Services

In the very first “Hello World” application in Chapter 1, we used a web service to exchange data between a client and server. However, to use web services with JavaScript to their fullest, you need to master some additional skills. These include error handling, inline web services (web service methods in the current .aspx page, also called page methods), and using web services and JavaScript without the help of the .NET Framework.

In this chapter, you will learn some special features of ASP.NET AJAX’s web services support, including error handling and maintaining session state. You will also see how to use non-ASP.NET web services with JavaScript.

Error Handling

Up to now, when working with web services, we expected our remote calls to work each time. However, the fact that an exception could be thrown has not yet been considered.

When using web services from remote servers (which, for the purposes of this dicussion means servers on another domain), developers often do not include exception-handling code. One reason is that a web service can be implemented with any technology, and every technology has its own way of running exceptions. Some do not raise exceptions at all.

However in the case of ASP.NET AJAX and Ajax, using web services is a bit different. We cannot directly use a remote service, since the security model prohibits us from doing so. By default, JavaScript and the XMLHttpRequest object only allow access to URIs within the same domain as the current ...