Validation

• Understanding Validation

• Validation Controls

• BaseValidator Class Properties

• Validator Specific Properties

• Validating with Regular Expressions

• Regular Expression Characters

• Commonly used Regular Expressions

• Validation Summary Control

• Manual Validation

• Validation Groups

Understanding Validation

Validation means ensuring that the data inserted into an application satisfies defined formats and other input criteria.

Some possible mistakes a user can make:

• Users might ignore an important field and leave it blank.

• Users might try to type a short string of nonsense to circumvent a required field check.

• Enter a nonnumeric character in a number field.• Malicious users might try to exploit a weakness in

your code by entering carefully structured wrong values

Validation Controls

ASP.NET provides five validator controls. Four are targeted at specific types of validation, while the fifth allows you to apply custom validation routines

BaseValidator classAll the validation controls are found in the

System.Web.UI.WebControls namespace and inherit from the BaseValidator class.

Property Description

ControlToValidate Identifies the control that is to be validated

Error Message If validation fails, the validator control can display a text message set by this property

ForeColor By changing the ForeColor, you can make the errormessage stand out

Display Dynamic, Static or None

IsValid Returns true or false depending on whether itsucceeded or failed

Enabled When set to false, automatic validation will not be performed for this control when the page is submitted

EnableClientScript If set to true, ASP.NET will add JavaScript and DHTML code to allow client-side validation on browsers that support it.

Validator-Specific Properties

Validating with Regular Expressions

One of ASP.NET’s most powerful validation controls is the RegularExpressionValidator, which validates text by determining whether it matches a specific pattern.

333\s\d\d\d\s represents any whitespace character (such as a space or tab). \d represents any digit

You can use the plus (+) sign to represent a repeated character. For example, 5+7 means “one or more occurrences of the character 5, followed by a single 7.” The number 57 would match, as would 555557

The following expression would match any word that starts with aletter from a to f, contains one or more “word” characters (letters), and ends with ing—possible matches include acting and developing.[a-f]\w+ing

Regular Expression Characters

Commonly used Regular Expressions

Client Side Validation

In some modern browsers, ASP.NET automatically adds JavaScript code for client-side validation. In this case, when the user clicks a CausesValidation button, the same error messages will appear without the page needing to be submitted and returned from the server. This increases the responsiveness of your web page.

However, even if the page validates successfully on the client side, ASP.NET still revalidates it when it’s received at the server.

CauseValidation PropertyWhat happens when the user clicks a button :

• If CausesValidation is false, ASP.NET will ignore the validation controls, the page will be posted back, and your event handling code will run normally.

• If CausesValidation is true (the default), ASP.NET will automatically validate the page when the user clicks the button. It does this by performing the validation foreach control on the page. If any control fails to validate, ASP.NET will return the page with some error information. Your click event handling code may or may not be executed.Use IsValid property in a conditional logic and write event handling code inside it.

Validation Summary ControlAccommodates all the error messages from all

the validation controls at a suitable location normally at the bottom of the page.

Error messages from all the validators are hided by setting their Display property to None.

When you run the page, you won’t see any dynamic messages as you enter invalid information andtab to a new field. However, when you click the OK button, the ValidationSummary will appear with a listof all error messages.

It automatically retrieves the value of the ErrorMessage property from each validator

Validation Summary Control

In some cases, you’ll want to display a full message in the summary and some sort of visual indicator next to the offending control

You can use this technique with the help of the Text property of the validators. Ordinarily, Text is left empty, and the validator doesn’t show any content in the web page. However, if you set both Text and ErrorMessage, the ErrorMessage value will be used for the summary while the Text value is displayed in the validator.

Of course, you’ll need to make sure you aren’t also setting the Display property of your validator to None.

Manual ValidationManual validation is when you disable validation and

perform the work on your own. This allows you to create a specialized error message of your own.You can create manual validation in one of three ways:

I. Use your own code to verify values. In this case, you won’t use any of the ASP.NET validation controls.

II. Disable the EnableClientScript property for each validation control. This allows an invalid page to be submitted, after which you can decide what to do with itdepending on the problems that may exist.

III. Add a button with CausesValidation set to false. When this button is clicked, manually validate the page by calling the Page.Validate() method. Then examine the IsValid property, and decide what to do.

Validation Groups

Every control that provides a CausesValidation property also includes the ValidationGroup property.

In some situations you might have several distinct groups of controls, possibly in separate panels and you may want to perform validations separately.

To create a validation group, you need to set the ValidationGroup property of every control in the same logical group with the same descriptive string.