ASP.NET 4 Unleashed

Creating an AjaxValidator Control

In this section, we create an extremely useful control named the AjaxValidator control. Like the CustomValidator control, the AjaxValidator control enables you to create a custom server-side validation function. Unlike the CustomValidator control, however, the AjaxValidator control enables you to call the custom validation function from the browser.

The AjaxValidator control uses AJAX (Asynchronous JavaScript and XML) to call the server-side validation function from the client. The advantage of using AJAX is that no postback to the server is apparent to the user.

For example, imagine that you create a website registration form and you need to validate a User Name field. You want to make sure that the User Name ...