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ASP.NET RequiredFieldValidator Control

This validator is used to make an input control required. It will throw an error if user leaves input control empty.

It is used to mandate form control required and restrict the user to provide data.

Note: It removes extra spaces from the beginning and end of the input value before validation is performed.

The ControlToValidateproperty should be set with the ID of control to validate.

RequiredFieldValidator Properties

Property	Description
AccessKey	It is used to set keyboard shortcut for the control.
BackColor	It is used to set background color of the control.
BorderColor	It is used to set border color of the control.
Font	It is used to set font for the control text.
ForeColor	It is used to set color of the control text.
Text	It is used to set text to be shown for the control.
ToolTip	It displays the text when mouse is over the control.
Visible	To set visibility of control on the form.
Height	It is used to set height of the control.
Width	It is used to set width of the control.
ErrorMessage	It is used to set error message that display when validation fails.
ControlToValidate	It takes ID of control to validate.

Example

Here, in the following example, we are explaining RequiredFieldValidator control and creating to mandatory TextBox controls.

// RequiredFieldValidator.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="RequiredFieldValidator.aspx.cs" 
Inherits="asp.netexample.RequiredFieldValidator" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<style type="text/css">
.auto-style1 {
width: 100%;
        }
.auto-style2 {
width: 165px;
        }
</style>
</head>
<body>
<form id="form1" runat="server">
<div>
</div>
<table class="auto-style1">
<tr>
<td class="auto-style2">User Name</td>
<td>
<asp:TextBox ID="username" runat="server"></asp:TextBox>
<asp:RequiredFieldValidatorID="user" runat="server" ControlToValidate="username" 
ErrorMessage="Please enter a user name" ForeColor="Red"></asp:RequiredFieldValidator>
</td>
</tr>
<tr>
<td class="auto-style2">Password</td>
<td>
<asp:TextBox ID="password" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="pass" runat="server" ControlToValidate="password" ErrorMessage="Please enter a password" 
ForeColor="Red"></asp:RequiredFieldValidator>
</td>
</tr>
<tr>
<td class="auto-style2"> </td>
<td>
<br/>
<asp:Button ID="Button1" runat="server" Text="login"/>
</td>
</tr>
</table>
</form>
</body>
</html>

Output:

It produces the following output when view in the browser.