ASP.NET in a Nutshell

Name

RequiredFieldValidator

Synopsis

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.

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 : Inherits BaseValidator
' Public Constructors
   Public Sub New() 
' Public Instance Properties
   Public Property InitialValue As String  
' Protected Instance Methods
   Overrides Protected Sub AddAttributesToRender(
        ByVal writer As System.Web.UI.HtmlTextWriter) 
   Overrides Protected Function EvaluateIsValid() As Boolean  
End Class

Hierarchy

System.Object→ System.Web.UI.Control(System.ComponentModel.IComponent, System.IDisposable, System.Web.UI.IParserAccessor, System.Web.UI.IDataBindingsAccessor)→WebControl(System.Web.UI.IAttributeAccessor)→Label→BaseValidator(System.Web.UI.IValidator)→ RequiredFieldValidator