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Professional ASP.NET 3.5 in C# and Visual Basic Part 95

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Professional ASP.NET 3.5 in C# and Visual Basic Part 95. Building on the revolutionary ASP.NET 2.0 release, ASP.NET 3.5 adds several key new developer features including AJAX, LINQ, and a new CSS designer in Visual Web Developer 2008. The dramatic reduction in code that developers realized from the more than 50 new server controls in ASP.NET 2.0 now allows developers the time to make their applications more interactive with AJAX, to work with data in their preferred language with LINQ, and to build visually attractive and consistent standards-based sites with CSS. . | Chapter 19 ASP.NET AJAX AJAX is dependent upon a few technologies in order for it to work. The first is the XMLHttpRequest object. This object allows the browser to communicate to a back-end server and has been available in the Microsoft world since Internet Explorer 5 through the MSXML ActiveX component. Of course the other major component is JavaScript. This technology provides the client-side initiation to communication with the back-end services and takes care of packaging a message to send to any server-side services. Another aspect of AJAX is support for DHTML and the Document Object Model DOM . These are the pieces that will change the page when the asynchronous response is received from the server. Finally the last piece is the data that is being transferred from the client to the server. This is done in XML or more important JSON. Support for the XMLHttpRequest object gives JavaScript functions within the client script library the capability to call server-side events. As stated typically HTTP requests are issued by a browser. It is also the browser that takes care of processing the response that comes from the server and then usually regenerates the entire Web page in the browser after a response is issued. This process is detailed in Figure 19-3. Figure 19-3 898 Chapter 19 ASP.NET AJAX If you use the XMLHttpRequest object from your JavaScript library you do not actually issue full page requests from the browser. Instead you use a client-side script engine which is basically a JavaScript function to initiate the request and also to receive the response. Because you are also not issuing a request and response to deal with the entire Web page you can skip a lot of the page processing because it is not needed. This is the essence of an AJAX Web request. It is illustrated in Figure 19-4. Figure 19-4 As stated this opens the door to a tremendous number of possibilities. Microsoft has provided the necessary script engines to automate much of the communication .