Home > Articles

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

Performing Custom Validation: The CustomValidator Control

The Validation controls included with ASP.NET enable you to handle a wide range of validation tasks. However, you cannot perform certain types of validation with the included controls. To handle any type of validation that is not covered by the standard validation controls, you need to use the CustomValidator control. All the properties, methods, and events of this control are listed in Table 3.6.

Table 3.6 CustomValidator, Properties, Methods, and Events

Properties

Description

ClientValidationFunction

Specifies the name of a client-side validation function.

ControlToValidate

Specifies the ID of the control that you want to validate.

Display

Sets how the error message contained in the Text property is displayed. Possible values are Static, Dynamic, and None; the default value is Static.

EnableClientScript

Enables or disables client-side form validation. This property has the value True by default.

Enabled

Enables or disables both server and client-side validation. This property has the value True by default.

ErrorMessage

Specifies the error message that is displayed in the ValidationSummary control. This error message is displayed by the control when the Text property is not set.

IsValid

Has the value True when the validation check succeeds and False otherwise.

Text

Sets the error message displayed by the control.

Methods

Description

OnServerValidate

Raises the ServerValidate event.

Validate

Performs validation and updates the IsValid property.

Events

Description

ServerValidate

Represents the function for performing the server-side validation.


You cannot use any of the included Validation controls, for example, with information that is stored in a database table. Typically, you want users to enter a unique username and/or e-mail address when completing a registration form. To determine whether a user has entered a unique username or e-mail address, you must perform a database lookup.

Using the CustomValidator control, you can write any subroutine for performing validation that you wish. The validation can be performed completely server-side. Alternatively, you can write a custom client-side validation function to use with the control. You can write the client-side script using either JavaScript or VBScript.

To create the server-side validation routine, you'll need to create a Visual Basic subroutine that looks like this:

Sub CustomValidator_ServerValidate( s As object, e As ServerValidateEventArgs )
End Sub

This subroutine accepts a special ServerValidateEventArgs parameter that has the following two properties:

  • IsValid—When this property is assigned the value True, the control being validated passes the validation check.

  • Value—The value of the control being validated.

CAUTION

The custom validation subroutine is not called when the control being validated does not contain any data. The only control that you can use to check for an empty form field is the RequiredFieldValidator control.

For this example, create a custom validation subroutine that checks for the string ASP.NET Unleashed. If you enter text into a TextBox control and it does not contain the name of this book, it fails the validation test.

First, you need to create a server-side version of the validation subroutine:

Sub CustomValidator_ServerValidate( s As Object, e As ServerValidateEventArgs )
 Dim strValue As String

 strValue = e.Value.ToUpper()
 If strValue.IndexOf( "ASP.NET UNLEASHED" ) > -1 Then
  e.IsValid = True
 Else
  e.IsValid = False
 End If
End Sub

This subroutine checks whether the string ASP.NET Unleashed appears in the value of the control being validated. If it does, the value True is assigned to the IsValid property; otherwise, the value False is assigned.

You could just implement custom validation with the server-side validation subroutine, which is all you need to get the CustomValidator control to work. However, if you want to get really fancy, you could implement it in a client-side script as well.

Be fancy. This VBScript client-side script implements the validation subroutine:

<Script Language="VBScript">
Sub CustomValidator_ClientValidate( s, e )
 Dim strValue

 strValue = UCase( e.Value )
 If Instr( strValue, "ASP.NET UNLEASHED" ) > 0 Then
  e.IsValid = True
 Else
  e.IsValid = False
 End If
End Sub
</Script>

This subroutine performs exactly the same task as the previous server-side validation subroutine; however, it is written in VBScript rather than Visual Basic.

After you create your server-side and client-side subroutines, you can hook them up to your CustomValidator control by using the OnServerValidate and ClientValidationFunction properties.

The page in Listing 3.19 illustrates how you can use the custom validation subroutines you just built.

Listing 3.19 CustomValidator.aspx

<Script Runat="Server">

Sub Button_Click( s As Object, e As EventArgs )
 If IsValid Then
  Response.Redirect( "ThankYou.aspx" )
 End If
End Sub

Sub CustomValidator_ServerValidate( s As Object, e As ServerValidateEventArgs )
 Dim strValue As String

 strValue = e.Value.ToUpper()
 If strValue.IndexOf( "ASP.NET UNLEASHED" ) > -1 Then
  e.IsValid = True
 Else
  e.IsValid = False
 End If
End Sub

</script>

<html>
<head>

<Script Language="VBScript">
Sub CustomValidator_ClientValidate( s, e )
 Dim strValue

 strValue = UCase( e.Value )
 If Instr( strValue, "ASP.NET UNLEASHED" ) > 0 Then
  e.IsValid = True
 Else
  e.IsValid = False
 End If
End Sub
</Script>

<title>CustomValidator.aspx</title>
</head>
<body>

<form Runat="Server">

Enter the name of your favorite book:
<br>
<asp:CustomValidator
 ControlToValidate="txtFavBook"
 ClientValidationFunction="CustomValidator_ClientValidate"
 OnServerValidate="CustomValidator_ServerValidate"
 Display="Dynamic"
 Text="You must type ASP.NET Unleashed!" 
 Runat="Server" />

<br>
<asp:TextBox
 ID="txtFavBook"
 TextMode="Multiline"
 Columns="50"
 Rows="3"
 Runat="Server" />

<p>
<asp:Button
 Text="Submit!"
 OnClick="Button_Click"
 Runat="Server" />

</form>
</body>
</html>

The C# version of this code can be found on the CD-ROM.

Validating Credit Card Numbers

In this section, you look at a slightly more complicated but more realistic application of the CustomValidator control. You learn how to write a custom validation function that checks whether a credit card number is valid.

The function uses the Luhn algorithm to check whether a credit card is valid. This function does not check whether credit is available in a person's credit card account. However, it does check whether a string of credit card numbers satisfies the Luhn algorithm, an algorithm that the numbers in all valid credit cards must satisfy.

The page in Listing 3.20 contains a TextBox control that is validated by a CustomValidator. If you enter an invalid credit card number, the validation check fails and an error message is displayed.

NOTE

You can test the form contained in Listing 3.20 by entering your personal credit card number or by entering the number 8 repeated 16 times.

Listing 3.20 CustomValidatorLuhn.aspx

<Script Runat="Server">

Sub Button_Click( s As Object, e As EventArgs)
 If IsValid Then
  Response.Redirect( "Thankyou.aspx" )
 End If
End Sub

Sub ValidateCCNumber( s As Object, e As ServerValidateEventArgs )
 Dim intCounter As Integer
 Dim strCCNumber As String
 Dim blnIsEven As Boolean = False
 Dim strDigits As String = ""
 Dim intCheckSum As Integer = 0

 ' Strip away everything except numerals
 For intCounter = 1 To Len( e.Value )
  If IsNumeric( MID( e.Value, intCounter, 1 ) ) THEN
   strCCNumber = strCCNumber & MID( e.Value, intCounter, 1 )
  End If
 Next

 ' If nothing left, then fail
 If Len( strCCNumber ) = 0 Then
  e.IsValid = False
 Else

 ' Double every other digit
 For intCounter = Len( strCCNumber ) To 1 Step -1
 If blnIsEven Then
  strDigits = strDigits & cINT( MID( strCCNumber, intCounter, 1 ) ) * 2
 Else
  strDigits = strDigits & cINT( MID( strCCNumber, intCounter, 1 ) )
 End If
 blnIsEven = ( NOT blnIsEven )
 Next

 ' Calculate CheckSum
 For intCounter = 1 To Len( strDigits )
  intCheckSum = intCheckSum + cINT( MID( strDigits, intCounter, 1 ) )
 Next

 ' Assign results
 e.IsValid = (( intCheckSum Mod 10 ) = 0 ) 

 End If
End Sub

</script>

<html>
<head><title>CustomValidatorLuhn.aspx</title></head>
<body>

<form Runat="Server">

Enter your credit card number:
<br>
<asp:TextBox
 ID="txtCCNumber"
 Columns="20"
 MaxLength="20"
 Runat="Server" />

<asp:CustomValidator
 ControlToValidate="txtCCNumber"
 OnServerValidate="ValidateCCNumber"
 Display="Dynamic"
 Text="Invalid Credit Card Number!"
 Runat="Server" />
<p>
<asp:Button
 Text="Submit!"
 OnClick="Button_Click" 
 Runat="Server" />
</form>

</body>
</html>

The C# version of this code can be found on the CD-ROM.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020