Most of the web sites you have built in this book have been confined to a single page. In Chapter 6, you learned techniques to provide a single look and feel throughout the site.
When you created the examples in Chapter 6, you may have noticed that any data you entered on a page usually didn't stick around if you went to a different page and came back, or even if you issued a postback on the page you were on. That's because the pages you've built up until now haven't had any way to preserve that kind of information, called state.
In each chapter up until now, you've learned about the different kinds of controls and how you use them. We're going to take a slightly different approach in this chapter, and first taking you behind the scenes so you can understand what the page actually does when you click the Submit button. Then you'll find out more about state, and how to hold onto it. By the time you've finished this chapter, you'll have built several sites that can retain state, no matter how much the user clicks around.
A user sits at her browser and types in a URL. A web page appears with text, and images, and buttons, and so forth. She fills in a text box and clicks a button. New data appears in response. How does this work?
Before we begin, it is important to understand a little bit about the "architecture" of the World Wide Web. In the applications you've developed to this point, you've been able to do everything on one computer. But ...