RequiredFieldValidator.EvaluateIsValid Method ()

 

Called during the validation stage when ASP.NET processes a Web Form.

Namespace:   System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

protected override bool EvaluateIsValid()

Return Value

Type: System.Boolean

true if the value in the input control is valid; otherwise, false.

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.CS.Controls" Assembly="Samples.AspNet.CS" %>
<%@ Page Language="C#" 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 - C# Example</title>
    <script runat="server">
      void Button1_Click(Object sender, EventArgs e) 
      {
        if (Page.IsValid) 
        {
          Label1.Text = "Required field is filled!";
        }
        else 
        {
          Label1.Text = "Required field is empty!";
        }
      }
    </script>
  </head>
  <body>
    <form id="Form1" method="post" runat="server">
      <h3>Custom RequiredFieldValidator - EvaluateIsValid - C# 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>&nbsp;</td>
          <td>
            <asp:Button 
              id="Button1" 
              runat="server" 
              Text="Validate" 
              OnClick="Button1_Click" />
          </td>
          <td>&nbsp;</td>
        </tr>
      </table>

    </form>
  </body>
</html>
using System.Web;
using System.Security.Permissions;

namespace Samples.AspNet.CS.Controls
{
  [AspNetHostingPermission(SecurityAction.Demand, Level=AspNetHostingPermissionLevel.Minimal)]
  public sealed class CustomRequiredFieldValidatorEvaluateIsValid : System.Web.UI.WebControls.RequiredFieldValidator
  {
    protected override bool EvaluateIsValid()
    {
      // Get the ControlToValidate's value.
      string controlValue = GetControlValidationValue(ControlToValidate);

      // If ControlToValidate's value is null or empty, then return false.
      if ((controlValue == null) || (controlValue.Trim().Equals(System.String.Empty)))
      {
        return false;
      }
      // Else the control contains a value so return true.
      else
      {
        return true;
      }
    }                
  }
}

.NET Framework
Available since 1.1
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