RequiredFieldValidator.EvaluateIsValid Method ()
.NET Framework (current version)
Called during the validation stage when ASP.NET processes a Web Form.
Assembly: System.Web (in System.Web.dll)
The following code example demonstrates how to override the EvaluateIsValid method in a custom server control so that it always returns false if the value of the RequiredFieldValidator is null or empty, and always returns true otherwise.
<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.VB.Controls" Assembly="Samples.AspNet.VB" %> <%@ Page Language="VB" AutoEventWireup="True" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head> <title>Custom RequiredFieldValidator - EvaluateIsValid - VB.NET Example</title> <script runat="server"> Sub Button1_Click(sender As Object, e As EventArgs) If Page.IsValid Then Label1.Text = "Required field is filled!" Else Label1.Text = "Required field is empty!" End If End Sub </script> </head> <body> <form id="Form1" method="post" runat="server"> <h3>Custom RequiredFieldValidator - EvaluateIsValid - VB.NET Example</h3> <table border="0" cellpadding="4" cellspacing="0"> <tr valign="top"> <td colspan="3"> <asp:Label ID="Label1" runat="server" Text="Fill in the required field below" /> </td> </tr> <tr> <td align="right">Card Number:</td> <td> <asp:TextBox id="TextBox1" runat="server" /> </td> <td> <aspSample:CustomRequiredFieldValidatorEvaluateIsValid id="RequiredFieldValidator1" runat="server" ControlToValidate="TextBox1" Display="Static" ErrorMessage="*" /> </td> </tr> <tr> <td> </td> <td> <asp:Button id="Button1" runat="server" Text="Validate" OnClick="Button1_Click" /> </td> <td> </td> </tr> </table> </form> </body> </html>
Imports System.Web Imports System.Security.Permissions Namespace Samples.AspNet.VB.Controls <AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal)> _ Public NotInheritable Class CustomRequiredFieldValidatorEvaluateIsValid Inherits System.Web.UI.WebControls.RequiredFieldValidator Protected Overrides Function EvaluateIsValid() As Boolean ' Get the ControlToValidate's value. Dim controlValue As String = GetControlValidationValue(ControlToValidate) ' If ControlToValidate's value is null or empty, then return false. If controlValue Is Nothing OrElse controlValue.Trim().Equals(System.String.Empty) Then Return False Else ' Else the control contains a value so return true. Return True End If End Function End Class End Namespace
.NET Framework
Available since 1.1
Available since 1.1
Show: