ASP.NET Validation

In this chapter, we will discuss about the data validation in the Web Forms. To perform validation, ASP.NET provides controls that automatically check user input and require no code. We can also create custom validation for our application.

ASP.NET validation controls

Following are the validation controls

Validator	Description
CompareValidator	It is used to compare the value of an input control against a value of another input control.
RangeValidator	It evaluates the value of an input control to check the specified range.
RegularExpressionValidator	It evaluates the value of an input control to determine whether it matches a pattern defined by a regular expression.
RequiredFieldValidator	It is used to make a control required.
ValidationSummary	It displays a list of all validation errors on the Web page.

ASP.NET CompareValidator Control

This validator evaluates the value of an input control against another input control on the basis of specified operator.

We can use comparison operators like: less than, equal to, greater than etc.

Note: If the input filed is empty, no validation will be performed.

CompareValidator Properties

Property	Description
AccessKey	It is used to set keyboard shortcut for the control.
TabIndex	The tab order of the control.
BackColor	It is used to set background color of the control.
BorderColor	It is used to set border color of the control.
BorderWidth	It is used to set width of border 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.
ControlToCompare	It takes ID of control to compare with.
ControlToValidate	It takes ID of control to validate.
ErrorMessage	It is used to display error message when validation failed.
Operator	It is used set comparison operator.

Example

Here, in the following example, we are validating user input by using CompareValidator controller. Source code of the example is given below.

// compare_validator_demo.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="compare_validator_demo.aspx.cs" 
Inherits="asp.netexample.compare_validator_demo" %>
<!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 {
height: 26px;
        }
.auto-style3 {
height: 26px;
width: 93px;
        }
.auto-style4 {
width: 93px;
        }
</style>
</head>
<body>
<form id="form1" runat="server">
<table class="auto-style1">
<tr>
<td class="auto-style3">
                        First value</td>
<td class="auto-style2">
<asp:TextBox ID="firstval" runat="server" required="true"></asp:TextBox>
</td>
</tr>
<tr>
<td class="auto-style4">
      Second value</td>
<td>
<asp:TextBox ID="secondval" runat="server"></asp:TextBox>
       It should be greater than first value</td>
</tr>
<tr>
<td class="auto-style4"></td>
<td>
<asp:Button ID="Button1" runat="server" Text="save"/>
</td>
</tr>
</table>
< asp:CompareValidator ID="CompareValidator1" runat="server" ControlToCompare="secondval" 
ControlToValidate="firstval" Display="Dynamic" ErrorMessage="Enter valid value" ForeColor="Red" 
Operator="LessThan" Type="Integer"></asp:CompareValidator>
</form>
</body>
</html>

Output: