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RequiredFieldValidator.AddAttributesToRender Method

Adds the HTML attributes and styles that need to be rendered for the control to the specified HtmlTextWriter object.

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

protected override void AddAttributesToRender(
	HtmlTextWriter writer


Type: System.Web.UI.HtmlTextWriter
A HtmlTextWriter that represents the output stream to render HTML content on the client.

The following code example demonstrates how to override the AddAttributesToRender method in a custom server control so that the RequiredFieldValidator error message always displays as bold.

Security noteSecurity Note

This example has a text box that accepts user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. For more information, see Script Exploits Overview.

<%@ 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"
<html xmlns="" >
    <title>Custom RequiredFieldValidator - AddAttributesToRender - C# Example</title>
    <script runat="server">
      void Button1_Click(Object sender, EventArgs e) 
        if (Page.IsValid) 
          Label1.Text = "Required field is filled!";
          Label1.Text = "Required field is empty!";
    <form id="Form1" method="post" runat="server">
      <h3>Custom RequiredFieldValidator - AddAttributesToRender - 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 align="right">Card Number:</td>
            <asp:TextBox id="TextBox1" runat="server" />
              ErrorMessage="Required" />
            <asp:Button id="Button1" runat="server" Text="Validate" OnClick="Button1_Click" />



using System.Web;
using System.Security.Permissions;

namespace Samples.AspNet.CS.Controls
  [AspNetHostingPermission(SecurityAction.Demand, Level=AspNetHostingPermissionLevel.Minimal)]
  public sealed class CustomRequiredFieldValidatorAddAttributesToRender : System.Web.UI.WebControls.RequiredFieldValidator
    protected override void AddAttributesToRender(System.Web.UI.HtmlTextWriter writer)
      // Show the RequiredFieldValidator's error message as bold.
      writer.AddStyleAttribute(System.Web.UI.HtmlTextWriterStyle.FontWeight, "bold");

      // Call the Base's AddAttributesToRender method.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.