Introduction
Input validation is very common and important in any kind of application. In the case of web applications, server side validation is a must, and client side validation is highly anticipated. As you know, ASP.NET provides you with a handful of validation controls like RequiredFiledValidator, RegularExpressionValidator etc. Most of the time, we have to check whether the user has given the correct number, date, time, or anything as input. To validate such things, we use the RegularExpressionValidator.
In this article, I'll provide a Util class full of Regular Expressions for the most common input validation requirements. The main part is the length validation of a TextArea control. As you know, in the case of a TextField, you can easily get its max length. But for TextArea, you cannot do that. So normally, we have to write a JavaScript function to check the length before form submit.
But in ASP.NET, when you use a TextBox and set the TextMode property as MultiLine, the MaxLength property does not work. So if you want to put a restriction to limit the input length of the TextBox, you have to find an alternate way.
Here, I'll show how you can do this by simply writing a Regular Expression.
The Code
The RegExp class:
using System;
using System.Collections.Generic;
using System.Text;
namespace Util
{
public class RegExp
{
public static readonly string Url = "[a-zA-Z0-9-_\\$]+(//.[a-za-z0-9-_//$]+)?\\??" +
"[a-zA-Z0-9-_\\$]+=?[a-zA-Z0-9-_\\$]+(&[a-zA-Z0-9-_\\$]+=" +
"[a-zA-Z0-9-_\\$]+)*";">\\.[a-zA-Z0-9-_\\$]+)?\\??" +
"[a-zA-Z0-9-_\\$]+=?[a-zA-Z0-9-_\\$]+(&" +
"[a-zA-Z0-9-_\\$]+=[a-zA-Z0-9-_\\$]+)*";
public static readonly string Date = "(0[1-9]|[12][0-9]|3[01])[-]" +
"(0[1-9]|1[012])[-]((175[7-9])|(17[6-9][0-9])|(1[8-9][0-9][0-9])|" +
"([2-9][0-9][0-9][0-9]))";
public static readonly string Time = "(0[1-9]|[1][0-2])[:]" +
"(0[0-9]|[1-5][0-9])[:](0[0-9]|[1-5][0-9])[ ][A|a|P|p][M|m]";
public static readonly string Number = "[-+]?[0-9]*\\.?[0-9]*";
public static readonly string Digit = "[0-9]*";
public static readonly string NonNegative = "[+]?[0-9]*\\.?[0-9]*";
public static string MaxLength(int len)
{
return "[\\s\\S]{0," + len.ToString() + "}";
}
}
}
The ValidationMessages class:
using System;
using System.Collections.Generic;
using System.Text;
namespace Resource
{
public class ValidationMessages
{
public static readonly string Url = "* Please enter a valid URL.<br>Valid " +
"characters are all alphanumeric characters and .?" +
"&_=-$<br> example: home.aspx?id=5&name=$my_name";
public static readonly string Required = "* Required";
public static readonly string Date =
"* Please enter a valid date in dd-MM-yyyy format.";
public static readonly string Time =
"* Please enter a valid time in hh:mm:ss am format.";
public static readonly string Number = "* Must be a valid number.";
public static readonly string Digit = "* Must be a valid whole number.";
public static readonly string NonNegative = "* Must be a non-negative number.";
public static string MaxLength(int len)
{
return "* Maximum " + len.ToString() +
" characters are allowed.";
}
}
}
Using the Code
The usage is very simple. See the example page.
Defaul.aspx page
<%@ Page Language="C#" AutoEventWireup="true"
CodeFile="Default.aspx.cs" Inherits="_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 runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<h3>
Validation Example</h3>
<table border="1" width="50%">
<tr>
<td style="width: 200px">
<asp:Label ID="CommentLabel"
runat="server" Text="Comment:">
</asp:Label></td>
<td>
<asp:TextBox ID="CommentTextBox" runat="server"
TextMode="MultiLine" Width="500px" />
<asp:RegularExpressionValidator ID="CommentValidator"
runat="server" ControlToValidate="CommentTextBox">
</asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
<asp:Label ID="DateLabel" runat="server"
Text="Date:"></asp:Label></td>
<td>
<asp:TextBox ID="DateTextBox"
runat="server" Width="500px" />
<asp:RegularExpressionValidator ID="DateValidator" runat="server"
ControlToValidate="DateTextBox"></asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
<asp:Label ID="TimeLabel" runat="server"
Text="Time:"></asp:Label></td>
<td>
<asp:TextBox ID="TimeTextBox"
runat="server" Width="500px" />
<asp:RegularExpressionValidator ID="TimeValidator" runat="server"
ControlToValidate="TimeTextBox"></asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
<asp:Label ID="NumberLabel" runat="server"
Text="Number:"></asp:Label></td>
<td>
<asp:TextBox ID="NumberTextBox"
runat="server" Width="500px" />
<asp:RegularExpressionValidator ID="NumberValidator" runat="server"
ControlToValidate="NumberTextBox">
</asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
<asp:Label ID="DigitLabel" runat="server"
Text="Digit:"></asp:Label></td>
<td>
<asp:TextBox ID="DigitTextBox"
runat="server" Width="500px" />
<asp:RegularExpressionValidator ID="DigitValidator" runat="server"
ControlToValidate="DigitTextBox"></asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
<asp:Label ID="NonNegativeLabel" runat="server"
Text="Non Negative:"></asp:Label></td>
<td>
<asp:TextBox ID="NonNegativeTextBox"
runat="server" Width="500px" />
<asp:RegularExpressionValidator
ID="NonNegativeValidator" runat="server"
ControlToValidate="NonNegativeTextBox">
</asp:RegularExpressionValidator>
</td>
</tr>
<tr>
<td>
<asp:Label ID="UrlLabel" runat="server" Text="Url:">
</asp:Label></td>
<td>
<asp:TextBox ID="UrlTextBox"
runat="server" Width="500px" />
<asp:RegularExpressionValidator ID="UrlValidator" runat="server"
ControlToValidate="UrlTextBox"></asp:RegularExpressionValidator>
</td>
</tr>
</table>
</div>
</form>
</body>
</html>
Defaul.aspx.cs page
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using Util;
using Resource;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
CommentValidator.ValidationExpression = RegExp.MaxLength(50);
CommentValidator.ErrorMessage = ValidationMessages.MaxLength(50);
DateValidator.ValidationExpression = RegExp.Date;
DateValidator.ErrorMessage = ValidationMessages.Date;
TimeValidator.ValidationExpression = RegExp.Time;
TimeValidator.ErrorMessage = ValidationMessages.Time;
NumberValidator.ValidationExpression = RegExp.Number;
NumberValidator.ErrorMessage = ValidationMessages.Number;
DigitValidator.ValidationExpression = RegExp.Digit;
DigitValidator.ErrorMessage = ValidationMessages.Digit;
NonNegativeValidator.ValidationExpression = RegExp.NonNegative;
NonNegativeValidator.ErrorMessage = ValidationMessages.NonNegative;
UrlValidator.ValidationExpression = RegExp.Url;
UrlValidator.ErrorMessage = ValidationMessages.Url;
}
}
Screenshot
Here, the URL validator expression and message were needed for my business requirements. If you have a different requirement, then customize it.
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