Beginning ASP.NET 3.5: In C# and VB

4.4. The ASP.NET State Engine

In the previous chapter, you created a page with a TextBox and a Button control. In the Try It Out, you ran this page in the browser, typed some text, and clicked the button. The button caused a postback to the server, and when the page reloaded, the text was still present in the text box. You pretty much did the same thing with the Wizard control in this chapter, where the values from the text box and the drop-down list were maintained as well. If you're familiar with other web technologies like ASP or PHP, this probably surprised you. In those languages, you often need to write lots of code to make this happen. So why and how does this work automatically in ASP.NET?

The text in the text box is maintained by the ASP.NET state engine, a feature that is deeply integrated in the ASP.NET runtime. It enables controls to maintain their state across postbacks so their values and settings remain available after every postback of the page.

4.4.1. What Is State and Why Is It Important?

To understand state, it's important to realize that by design, HTTP — the protocol used to request and serve pages in a web browser — is stateless. What this means is that the web server does not keep track of requests that have been made from a specific browser. As far as the web server is concerned, each request you make to the server by browsing to a page and clicking links to other pages stands on its own. The web server has no recollection of pages you requested previously. ...