Build Your Own ASP.NET 2.0 Web Site Using C# & VB, Second Edition

Using the Validation Controls

6

Ever needed to ensure that a user typed an email address into a text box? Or

wanted to make sure that a user typed numbers only into a phone number field?

Validation involves checking that the data your application’s users have entered

obeys a number of predefined rules. To help developers with the most common

data validation tasks, ASP.NET provides a set of validation controls that ease

the problems that beset web developers in the past. This chapter will show you

how to use them.

There are two kinds of form validation, differentiated by where the validation

takes place. You could write client-side JavaScript code that validates the data

typed by the user directly into the browser (client-side validation), or you could

use server-side VB or C# code to validate the user input once the form has been

submitted to the server (server-side validation).

Client-side validation has its benefits, chief among them the fact that it provides

instant feedback to users. If users fail to enter their names into a text box, the

page automatically displays an error message. The users know immediately that

they need to enter their names—they don’t need to wait for a response from the

server to tell them so. The process is quick and efficient, and good for the overall

user experience.

However, there’s one big drawback with client-side validation: users must have

JavaScript enabled in their browsers, or validation simply will not occur. Some