RequiredFieldValidator.EvaluateIsValid Method
.NET Framework 2.0
Called during the validation stage when ASP.NET processes a Web Form.
Namespace: System.Web.UI.WebControls
Assembly: System.Web (in system.web.dll)
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.JSL.Controls" Assembly="Samples.AspNet.JSL" %>
<%@ Page Language="VJ#" AutoEventWireup="True" %>
<HTML>
<HEAD>
<title>Custom RequiredFieldValidator - EvaluateIsValid - VJ# Example</title>
<script runat="server">
void Button1_Click(Object sender, EventArgs e)
{
if (get_Page().get_IsValid()) {
Label1.set_Text("Required field is filled!");
}
else {
Label1.set_Text("Required field is empty!");
}
} //Button1_Click
</script>
</HEAD>
<body>
<form id="Form1" method="post" runat="server">
<h3>Custom RequiredFieldValidator - EvaluateIsValid - VJ# 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>
...package Samples.AspNet.JSL.Controls;
public class CustomRequiredFieldValidatorEvaluateIsValid
extends System.Web.UI.WebControls.RequiredFieldValidator
{
protected boolean EvaluateIsValid()
{
// Get the ControlToValidate's value.
String controlValue = GetControlValidationValue(get_ControlToValidate());
// If ControlToValidate's value is null or empty, then return false.
if (controlValue == null || controlValue.Trim().Equals("")) {
return false;
}
// Else the control contains a value so return true.
else {
return true;
}
} //EvaluateIsValid
} //CustomRequiredFieldValidatorEvaluateIsValid
Windows 98, Windows 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.
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