ASP.NET RequiredFieldValidator: Implementing Mandatory Input Fields in Web Forms

Learn how to use the ASP.NET RequiredFieldValidator control to ensure that users fill in essential form fields. This tutorial explains its functionality, key properties for customization (error message, display style, etc.), and how to integrate it into your web forms for robust and user-friendly input validation.

ASP.NET RequiredFieldValidator Control

What is RequiredFieldValidator?

The RequiredFieldValidator control in ASP.NET is used to make sure that a user fills in a particular input field. If the user leaves the field blank, it will display an error message.

It's essential for ensuring that required information is provided in forms. Before validation, the control automatically removes extra spaces from the beginning and end of the input.

RequiredFieldValidator Properties

The RequiredFieldValidator control has several properties to customize its appearance and behavior. Here are some of the key ones:

  • ControlToValidate: Specifies the ID of the input control that must be filled.
  • ErrorMessage: The message displayed when the field is left empty.
  • Other properties control appearance (e.g., BackColor, ForeColor, Font, ToolTip).

Example: RequiredFieldValidator

This example demonstrates using RequiredFieldValidator to make two text boxes (for username and password) mandatory.

RequiredFieldValidator.aspx (Example Code):

Code

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="RequiredFieldValidator.aspx.cs"
    Inherits="asp.netexample.RequiredFieldValidator" %>

User Name: <asp:TextBox ID="txtName" runat="server" />
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
    ControlToValidate="txtName" ErrorMessage="User Name is required!" ForeColor="Red"></asp:RequiredFieldValidator><br />

Password: <asp:TextBox ID="txtPassword" runat="server" TextMode="Password" />
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" 
    ControlToValidate="txtPassword" ErrorMessage="Password is required!" ForeColor="Red"></asp:RequiredFieldValidator><br />

This code adds a RequiredFieldValidator for each TextBox, ensuring that both username and password are entered.