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ASP.NET - Validation Controls

ASP.Net validation controls validate the user input data to ensure that useless, unauthenticated or contradictory data don.t get stored.

ASP.Net provides the following validation controls:

  1. RequiredFieldValidator

  2. RangeValidator

  3. CompareValidator

  4. RegularExpressionValidator

  5. CustomValidator

  6. ValidationSummary

The BaseValidator Class:

The validation control classes inherit from the BaseValidator class and inherit its properties and methods. Therefore, it would help to take a look at the properties and the methods of this base class, which are common for all the validation controls:

ControlToValidateIndicates the input control to validate.
Display Indicates how the error message is shown.
EnableClientScriptIndicates whether client side validation will take.
EnabledEnables or disables the validator.
ErrorMessageError string.
Text Error text to be shown if validation fails.
IsValidIndicates whether the value of the control is valid.
SetFocusOnErrorIt indicates whether in case of an invalid control, the focus should switch to the related input control.
ValidationGroupThe logical group of multiple validators, where this control belongs.
Validate()This method revalidates the control and updates the IsValid property.

The RequiredFieldValidator:

The RequiredFieldValidator control ensures that the required field is not empty. It is generally tied to a text box to force input into the text box.

The syntax for the control:

<asp:RequiredFieldValidator ID="rfvcandidate" 
        runat="server" ControlToValidate ="ddlcandidate"
        ErrorMessage="Please choose a candidate" 
        InitialValue="Please choose a candidate">

The RangeValidator:

The RangeValidator control verifies that the input value falls within a predetermined range.

It has three specific properties:

Typeit defines the type of the data; the available values are: Currency, Date, Double, Integer and String
MinimumValueit specifies the minimum value of the range
MaximumValueit specifies the maximum value of the range

The syntax for the control:

<asp:RangeValidator ID="rvclass" 
       ErrorMessage="Enter your class (6 - 12)" 
       MinimumValue="6" Type="Integer">

The CompareValidator:

The CompareValidator control compares a value in one control with a fixed value, or, a value in another control.

It has the following specific properties:

Typeit specifies the data type
ControlToCompareit specifies the value of the input control to compare with
ValueToCompareit specifies the constant value to compare with
Operatorit specifies the comparison operator, the available values are: Equal, NotEqual, GreaterThan, GreaterThanEqual, LessThan, LessThanEqual and DataTypeCheck

The basic syntax for the control:

<asp:CompareValidator ID="CompareValidator1" 

The RegularExpressionValidator

The RegularExpressionValidator allows validating the input text by matching against a pattern against a regular expression. The regular expression is set in the ValidationExpression property.

The following table summarizes the commonly used syntax constructs for regular expressions:

Character EscapesDescription
\bMatches a backspace
\t Matches a tab
\r Matches a carriage return
\vMatches a vertical tab
\fMatches a form feed
\nMatches a new line
\Escape character

Apart from single character match, a class of characters could be specified that can be matched, called the metacharacters.

.Matches any character except \n
[abcd]Matches any character in the set
[^abcd]Excludes any character in the set
[2-7a-mA-M]Matches any character specified in the range
\wMatches any alphanumeric character and underscore
\WMatches any non-word character
\sMatches whitespace characters like, space, tab, new line etc.
\SMatches any non-whitespace character
\dMatches any decimal character
\DMatches any non-decimal character

Quantifiers could be added to specify number of times a character could appear

*Zero or more matches
+One or more matches
?Zero or one matches
{N}N matches
{N,}N or more matches
{N,M}Between N and M matches

The syntax for the control:

<asp:RegularExpressionValidator ID="string"

The CustomValidator:

The CustomValidator control allows writing application specific custom validation routines for both the client side and the server side validation.

The client side validation is accomplished through the ClientValidationFunction property. The client side validation routine should be written in a scripting language, like JavaScript or VBScript, which the browser can understand.

The server side validation routine must be called from the control.s ServerValidate event handler. The server side validation routine should be written in any .Net language, like C# or VB.Net.

The basic syntax for the control

<asp:CustomValidator ID="CustomValidator1" 

The ValidationSummary Control

The ValidationSummary control does not perform any validation but shows a summary of all errors in the page. The summary displays the values of the ErrorMessage property of all validation controls that failed validation.

The following two mutually inclusive properties list out the error message:

  • ShowSummary: shows the error messages in specified format.

  • ShowMessageBox: shows the error messages in a separate window.

The syntax for the control:

<asp:ValidationSummary ID="ValidationSummary1" 
       DisplayMode = "BulletList" 
       ShowSummary = "true"
       HeaderText="Errors:" />

Validation Groups:

Complex pages have different groups of information provided in different panels. In such a situation a need for performing validation separately for separate group, might arise. This kind of situation is handled using validation groups.

To create a validation group, you should put the input controls and the validation controls into the same logical group by setting their ValidationGroup property.