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defined on a page are automatically grouped in the Validators collection of the Page class. You can validate them all in a single shot using the Validate method in the page class or individually by calling the Validate method on each validator. The Validate method sets the IsValid property both on the page and on the individual validator. The IsValid property indicates whether the user’s entries match the requirements of the validators. The user’s entry is validated when the Validate method is called and also whenever the page posts back.

Note

Typical control members involved with input validation have been grouped in the IValidator interface that the BaseValidator class implements. The interface includes the Validate method and the IsValid and ErrorMessage properties.

Generalities of Validation Controls

Each validation control references an input control located elsewhere on the page. When the page is submitted, the content of the monitored server control is passed to the associated validation control for further processing. Each validation control performs a different type of verification. Table 9-3 shows the types of validation supported by the .NET Framework.

Table 9-3. Validation Controls in ASP.NET

Validation Control

Description

CompareValidator

Compares the user’s entry against a fixed value by using a comparison operator such as LessThan, Equal, or GreaterThan. It can also compare against the value of a property in another control on the same page.

CustomValidator

Employs programmatically defined validation logic to check the validity of the user’s entry. You use this validator when the other validators cannot perform the necessary validation and you want to provide custom code that validates the input.

RangeValidator

Ensures that the user’s entry falls within a specified range. Lower and upper boundaries can be expressed as numbers, strings, or dates.

RegularExpressionValidator

Validates the user’s entry only if it matches a pattern defined by a regular expression.

RequiredFieldValidator

Ensures that the user specifies a value for the field.

Multiple validation controls can be used with an individual input control to validate according to different criteria. For example, you can apply multiple validation controls on a text box that is expected to contain an e-mail address. In particular, you can impose that the field is not skipped (RequiredFieldValidator) and that its content matches the typical format of e-mail addresses (RegularExpressionValidator).

Table 9-3 lacks a reference to the ValidationSummary control. The control does not perform validation tasks itself. Instead, it displays a label to summarize all the validation error messages found on a Web page as the effect of other validators. I’ll cover the ValidationSummary control later in the chapter.

The BaseValidator Class

Table 9-4 details the specific properties of validation controls. Some properties—such as ForeColor, Enabled, and Text—are overridden versions of base properties on base classes.

Table 9-4. Basic Properties of Validators

Property

Description

ControlToValidate

Gets or sets the input control to validate. The control is identified by name—that is, by using the value of the ID attribute.

Display

If client-side validation is supported and enabled, gets or sets how the space for the error message should be allocated—either statically or dynamically. In the case of server-side validation, this property is ignored. A Static display is possible only if the browser supports the display CSS style. The default is Dynamic.

EnableClientScript

True by default; gets or sets whether client-side validation is enabled.

Enabled

Gets or sets whether the validation control is enabled.

ErrorMessage

Gets or sets the text for the error message.

ForeColor

Gets or sets the color of the message displayed when validation fails.

IsValid

Gets or sets whether the associated input control passes validation.

SetFocusOnError

Indicates whether the focus is moved to the control where validation