Chapter 15. Programming ASP.NET Applications and Web Services

Developers are writing more and more of their applications to run over the Web.

There are many obvious advantages. For one, you don't have to create as much of the user interface; you can let Internet Explorer and other browsers handle a lot of the work for you. Another, perhaps bigger, advantage is that distribution of the application and of revisions is faster, easier, and less expensive. Most important, a web application can be run on any platform by any user at any location; this is harder to do (though not impossible) with smart-client applications.

The third advantage of web applications is distributed processing, though smart-client applications are making inroads. With a web-based application, it is easy to provide server-side processing, and the Web provides standardized protocols (e.g., HTTP, HTML, and XML) to facilitate building n-tier applications.

The .NET technology for building web applications (and dynamic web sites) is ASP.NET 2.0, which provides a rich collection of types for building web applications in its System.Web and System.Web.UI namespaces. There is a great deal to learn about ASP.NET, but much of it is language-independent. ASP.NET offers a rich suite of controls and related tools, including tools to validate data, display dates, present advertisements, interact with users, and so forth. Most of these require no coding whatsoever.

The focus of this chapter is where ASP.NET and C# programming intersect: the creation of Web Forms and web services. The role of the C# programmer in ASP.NET development is in writing the event handlers that respond to user interaction. Many of the event handlers will either add data to a database or retrieve data and make it available to the controls. For coverage of ASP.NET alone, see my book (co-written with Dan Hurwitz), Programming ASP.NET (O'Reilly).

Web Forms bring RAD techniques (such as those used in Windows Forms) to the development of web applications. As with Windows Forms, you drag-and-drop controls onto a form and write the supporting code either inline or in code-behind pages. With Web Forms, however, the application is deployed to a web server, and users interact with the application through a standard browser.

.NET web services expand on the concept of distributed processing to build components whose methods can be invoked across the Internet using industry-wide standard protocols. These components can be built in any .NET language,^[1] and they communicate using open protocols that are platform-independent. For example, a stock exchange server might provide a web service method that takes a stock ticker symbol as a parameter and returns a quote. An application might combine that service with another service from a different company that also takes a stock symbol but that returns background data about the company. The application developer can concentrate on adding value to these services, instead of duplicating the same service for his own application.

^[1] Web services can, of course, be written in any language on any platform; the point of web services is that they are platform-independent. For the purposes of this book, however, we will focus on creating and consuming web services using .NET.

This chapter demonstrates Web Forms and web services programming using C#.