Completing a Web Form in ASP.NET - How to run a web site with the built-in development server
(Page 5 of 5 )
When you run a file-system web site by using one of the techniques in figure 2-17, Visual Studio 2005 compiles the application. If the application compiles without errors, Visual Studio automatically launches the built-in ASP.NET 2.0 Development Server and displays the starting page of the web site in your default browser. Then, you can test the application to make sure that it works the way you want it to.
However, if any errors are detected as part of the compilation, Visual Studio opens the Error List window and displays the errors. These can consist of errors that have to be corrected as well as warning messages. In this figure, all of the errors have been corrected, but 7 warning messages are displayed in the Error List window.
To fix an error, you can double-click on it in the Error List window. This moves the cursor to the line of code that caused the error in the Code Editor. By moving from the Error List window to the Code Editor for all of the messages, you should be able to find the coding problems and fix them.
As you’re testing an application with the development server, exceptions may occur. If an exception isn’t handled by the application, ASP.NET switches to the Code Editor window and highlights the statement that caused the exception. In this case, you can end the application by clicking on the Stop Debugging button in the Debug toolbar or using the Debug->Stop Debugging command. Then, you can fix the problem and test again.
In chapter 4, you’ll learn all of the debugging skills that you’ll need for more complex applications. For simple applications, though, you should be able to get by with just the skills you have right now.
An ASP.NET project with the shortcut menu for a web form displayed
Figure 2-17. How to run a web site with the built-in development server
How to run an application
How to review the HTML that’s sent to the browser
To view the HTML for a page that’s displayed in a browser, you can use the Source command in your browser’s View menu. To illustrate, figure 2-18 presents the HTML that’s sent back to the browser after I selected a new value from the drop-down list, entered new values into the text boxes, and clicked the Calculate button. Although you’ll rarely need to view this code, it does give you a better idea of what’s going on behind the scenes.
First, you’ll see that this code doesn’t include any asp tags. That’s because these tags are rendered to standard HTML so the controls they represent can be displayed in the browser. For instance, the asp tag for the drop-down list in the first row of the table has been converted to an HTML select tag.
Second, you can see that the view state data is stored in a hidden input field named _ViewState. Here, the value of this field is encrypted so you can’t read it. Because the data in view state is passed to and from the browser automatically, you don’t have to handle the passing of this data in your code.
Third, you can see that the data that I selected from the drop-down list is included in the HTML. Although you can’t see it, the data that was entered into the text boxes is included as well. This illustrates that you don’t need view state to save the information that’s entered by the user. Instead, view state is used to maintain the state of properties that have been set by code. For example, it’s used to maintain the values that are loaded into the drop-down list the first time the user requests the form.
Keep in mind that this HTML is generated automatically by ASP.NET, so you don’t have to worry about it. You just develop the application by using Visual Studio in the way I’ve just described, and the rest of the work is done for you.
The HTML for the Future Value form after a post back
Figure 2-18. How to review the HTML that's sent to the browser
Description
- To view the HTML for a page, use the View->Source command in the browser’s menu.
- The HTML that the browser receives consists entirely of standard HTML tags because all of the ASP.NET tags are converted to standard HTML when the page is rendered.
- View state data is stored in a hidden input field within the HTML. This data is encrypted so you can’t read it.
- If the page contains validation controls and client scripting is enabled for those controls, the HTML for the page contains script to perform the validation on the client if the client supports DHTML.
- Values that the user enters into a page are returned to the browser as part of the HTML for the page.
| DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware. |
|
 This article is excerpted from the book Murach's ASP.NET 2.0 Web Programming with VB2005, written by Doug Lowe (Murach, 2006; ISBN: 1890774324). Check it out today at your favorite bookstore. Buy this book now.
|
|
/ 23 
