ASP.NET RegularExpressionValidator: Implementing Robust Input Validation

Learn how to use the ASP.NET RegularExpressionValidator control to implement powerful and flexible input validation in your web forms. This tutorial explains how to define validation patterns using regular expressions, handle various input types, and display error messages to ensure data integrity and a positive user experience.

ASP.NET RegularExpressionValidator Control

Introduction to RegularExpressionValidator

The RegularExpressionValidator control in ASP.NET is a server-side validation control used to verify that user input matches a specific pattern defined by a regular expression. Regular expressions are powerful tools for defining complex patterns of characters. This control is particularly useful for validating predictable text formats, like email addresses or phone numbers.

Key Properties of RegularExpressionValidator

The RegularExpressionValidator control has several key properties:

Property	Description
`AccessKey`	Sets a keyboard shortcut for the control.
`BackColor`	Sets the background color.
`BorderColor`	Sets the border color.
`Font`	Sets the font for the control text.
`ForeColor`	Sets the text color.
`Text`	Sets the text displayed by the control.
`ToolTip`	Text displayed when the mouse hovers over the control.
`Visible`	Controls whether the control is visible.
`Height`	Sets the height of the control.
`Width`	Sets the width of the control.
`ErrorMessage`	The error message displayed if validation fails.
`ControlToValidate`	The ID of the control to be validated.
`ValidationExpression`	The regular expression pattern to match.

Example: Validating an Email Address

This example demonstrates using a RegularExpressionValidator to validate an email address. The regular expression is used to check if the user input conforms to a valid email format.

ASPX Code (RegularExpressionDemo.aspx)


<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="RegularExpressionDemo.aspx.cs" Inherits="asp.netexample.RegularExpressionDemo" %>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server"
    ControlToValidate="TextBox1" ErrorMessage="Invalid Email Format"
    ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"
/>
<asp:Button ID="Button1" runat="server" Text="Submit" />

Output

(Screenshots illustrating both valid and invalid input scenarios, showing the error message when an invalid email format is entered, would be included here.)