ASP.NET.in.a.Nutshell.Second.Edition [Electronic resources] نسخه متنی

This class represents a validation control that is used to force user
entry in a corresponding input control, like a
TextBox. Validation fails if the value in the
input control does not differ from the
InitialValue property. By default,
InitialValue is set to
System.String.Empty, and validation will succeed
as long as some information has been added to the input control. In
this way, the RequiredFieldValidator control works
identically to the
System.Web.UI.WebControls.RequiredFieldValidator
control for full-fledged web pages (although it
won't render client-side validation code).

You can use a combination of different validation controls for a
single control. For example, you could use a
RequiredFieldValidator to ensure that a value is
entered, and a RangeValidator to ensure that the
value is within a specified data range. This is often required, as
validators like RangeValidator will automatically
validate a control if it is empty, regardless of the properties you
have set.

public class 
RequiredFieldValidator  : BaseValidator {
// Public Constructors
public 
RequiredFieldValidator ( );
// Public Instance Properties
public string 
InitialValue {set; get; }
// Protected Instance Methods
protected override BaseValidator 
CreateWebValidator ( );        // overrides BaseValidator
protected override bool 
EvaluateIsValid ( );       // overrides BaseValidator
}

Hierarchy

System.Object
System.Web.UI.Control(System.ComponentModel.IComponent,
System.IDisposable,
System.Web.UI.IParserAccessor,
System.Web.UI.IDataBindingsAccessor)

MobileControl(System.Web.UI.IAttributeAccessor)
TextControl
BaseValidator(System.Web.UI.IValidator)
RequiredFieldValidator