One of the most tiresome tasks when
building interactive web applications is the requirement for validating values
that the user enters into the input
controls. This is particularly the case if we need to perform
client-side as well as server side
validation. Mostly, we use JavaScript for client side coding.
Help is at hand with the range of
validation controls
that are included in ASP.NET.
They cover almost all the validation
scenarios. A validation
control enables us to validate an input and display an error message if
necessary. It is very much like other server-side
controls, with certain additional methods and
properties. First, the server treats it as an invisible control. After the user
has entered erroneous data, it becomes visible. It is a powerful, rapid
application development feature; however, a developer needs to understand its
behavior and the methods thoroughly before he or she can appreciate it. All the
validation
controls inherit from the
base class BaseValidator,
which is part of the class library namespace.
System.Web.UI.WebControls.BaseValidator
exposes a series of properties and methods that are common to all the
validation
controls.
RequiredFieldValidator
<asp:RequiredFieldValidator>
Checks that the validated control contains a value. It cannot be empty. Can be
used in conjunction with other validators on a control to trap empty values.
Simply, we can use it to check if the input control has any value. The most
important property in the
RequiredFieldValidator is
InitialValue.
<asp:TextBox
id="txtName"
runat="server"
/>
<asp:RequiredFieldValidator
id="validTxtName"
runat="server"
controlToValidate="txtName"
errorMessage="Please
enter Your Name"
display="static">
</asp:RequiredFieldValidator>
Summary
In this article I explained the basic concepts and usage of Validation controls
in ASP.NET.