In this blog we will know how to validate blank textbox using CustomValidator in ASP.Net.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="Blank__textbox_CustomValidator._Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head id="Head1" runat="server">

<title>Untitled Page</title>

</head>

<body>

<form id="form1" runat="server">

<div>

<div>

<asp:Label ID="lblName" Text="Name:" AssociatedControlID="txtName" runat="server" />

<br />

<asp:TextBox ID="txtName" runat="server" />

<asp:CustomValidator ID="cv_name" runat="server" ControlToValidate="txtName" Text="Name should not be blank"

ValidateEmptyText="true" OnServerValidate="cv_name_ServerValidate"></asp:CustomValidator><br />

<asp:Button ID="btnSubmit" Text="Submit" runat="server" />

</div>

</div>

</form>

</body>

</html>

.CS Code

using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

namespace Blank__textbox_CustomValidator

{

public partial class _Default : System.Web.UI.Page

{

protected void cv_name_ServerValidate(object source, ServerValidateEventArgs args)

{

if (args.Value.Length != 0)

args.IsValid = true;

else

args.IsValid = false;

}

}

}