ASP.NET MVC 4.0 Basic CAPTCHA VB.NET ASPX Code Sample (BotDetect v3.0; deprecated)

The ASP.NET MVC 4.0 Basic Captcha VB.NET ASPX sample project shows the most basic source code required to protect an ASP.NET MVC form with BotDetect CAPTCHA and validate the user input.

First Time Here?

Check the BotDetect ASP.NET MVC Captcha Quickstart for key integration steps.

ASP.NET MVC View code displaying CAPTCHA protection can be found in Views/Sample/Index.aspx, and the ASP.NET MVC Controller code checking user input is in Controllers/SampleController.vb.

→ ASP.NET MVC version:

→ .NET programming language:

  • C#
  • VB.NET

→ View engine:

Installed Location

By default, the .NET 4.5 VB.NET ASPX version of the ASP.NET MVC 4.0 Basic Captcha sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v4.5\WebApp\AspNetMvc40BasicCaptchaSample\ASPX\VBNet

You can also run it from the BotDetect Start Menu:
Programs > Lanapsoft > BotDetect 3 CAPTCHA Component > ASP.NET > DotNET 4.5 Web Applications > Run


<%@ Page Language="VB" Inherits="System.Web.Mvc.ViewPage" %>

<%-- namespaces needed to access BotDetect members --%>
<%@ Import namespace="BotDetect.Web.UI.Mvc" %>

<!DOCTYPE html>

<head runat="server">
    <meta name="viewport" content="width=device-width" />
    <title>BotDetect ASP.NET MVC 4.0 Basic CAPTCHA Sample ASPX VB.NET
    <link href="<%: Url.Content("~/Style/Sheet.css") %>" rel="stylesheet" 
      type="text/css" />
    <link href="<%: Url.Content("~/" + BotDetect.Web.CaptchaUrls.
      LayoutStyleSheetUrl) %>" rel="stylesheet" type="text/css" />
    <h1>BotDetect ASP.NET MVC 4.0 Basic CAPTCHA Sample</h1>

    <% Using Html.BeginForm() %>
            <legend>CAPTCHA Protection Shown on an ASP.NET MVC View</legend>
                <%: Html.Label("CaptchaCode", "Retype the code from the 
                  picture:") %>
                <% Dim sampleCaptcha As MvcCaptcha = _
                     New MvcCaptcha("SampleCaptcha")
                    sampleCaptcha.UserInputClientID = "CaptchaCode" %>
                <%: Html.Captcha(sampleCaptcha) %>
            <div class="actions">
                <%: Html.TextBox("CaptchaCode") %>
                <input type="submit" value="Validate" />
                <%: Html.ValidationMessage("CaptchaCode") %>
    <% End Using %>

To display Captcha protection on the sample View, we first ensure we can use BotDetect members by Import-ing the relevant namespaces.

We then create a MvcCaptcha instance, and add it to the form by calling the Html.Captcha() Html helper with it.

In this simplest case, we also use the Html.ValidationMessage helper to display Captcha validation errors.


Imports BotDetect.Web.UI.Mvc

Namespace AspNetMvc40BasicCaptchaSampleAspxVBNet
    Public Class SampleController
        Inherits System.Web.Mvc.Controller

        ' GET: /Sample

        Function Index() As ActionResult
            Return View()
        End Function

        ' POST: /Sample/

        <HttpPost()> _
        <CaptchaValidation("CaptchaCode", "SampleCaptcha", "Incorrect CAPTCHA 
          code!")> _
        Public Function Index(ByVal model As SampleModel) As ActionResult
            Return View(model)
        End Function

    End Class
End Namespace

After we've included the BotDetect.Web.UI.Mvc namespace, we just need to add the CaptchaValidation attribute to the method processing form submissions. The attribute takes three parameters:

  1. the ID of the textbox containing the user's Captcha code input (which we named CaptchaCode on the form),
  2. the ID of the Captcha instance we're validating (which we set to SampleCaptcha in the MvcCaptcha constructor), and
  3. the error message to be shown when Captcha validation fails.

When the Captcha validation action filter attribute has been added, the Captcha validation will trigger every time the form is submitted, and will automatically add a Model error with the error message configured above when Captcha validation fails. The Html.ValidationMessage helper on the form will then display this error when Captcha validation fails.


Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web
Imports System.Web.Mvc
Imports System.Web.Routing

Public Class RouteConfig
    Public Shared Sub RegisterRoutes(ByVal routes As RouteCollection)

        ' BotDetect requests must not be routed
          New With {.botdetect = "(.*)BotDetectCaptcha\.ashx"})

        routes.MapRoute( _
            name:="Default", _
            url:="{controller}/{action}/{id}", _
            defaults:=New With {.controller = "Sample", .action = "Index", 
              .id = UrlParameter.Optional} _
    End Sub
End Class

We configure ASP.NET Routing to ignore BotDetect requests, since they do not conform to any MVC-related patterns. The regex defining requests to ignore must match the path configured for the BotDetect HttpHandler registered in web.config.


<?xml version="1.0" encoding="utf-8"?>
  For more information on how to configure your ASP.NET application, please 
    <section name="botDetect" requirePermission="false" 
      type="BotDetect.Configuration.BotDetectConfigurationSection, BotDetect"/>
    <add key="webpages:Version" value="" />
    <add key="webpages:Enabled" value="false" />
    <add key="PreserveLoginUrl" value="true" />
    <add key="ClientValidationEnabled" value="true" />
    <add key="UnobtrusiveJavaScriptEnabled" value="true" />
    <httpRuntime targetFramework="4.5" />
    <compilation debug="true" targetFramework="4.5" />
    <!-- make sure Session State is enabled -->
    <pages enableSessionState="true">
        <add namespace="System.Web.Mvc" />
        <add namespace="System.Web.Mvc.Ajax" />
        <add namespace="System.Web.Mvc.Html" />
        <add namespace="System.Web.Routing" />
    <!-- configure Session State for BotDetect use -->
    <sessionState mode="InProc" cookieless="AutoDetect" timeout="20" 
      sessionIDManagerType="BotDetect.Web.CustomSessionIdManager, BotDetect"/>
      <!-- register HttpHandler used for BotDetect Captcha requests -->
      <add verb="GET" path="BotDetectCaptcha.ashx" 
        type="BotDetect.Web.CaptchaHandler, BotDetect"/>
    <validation validateIntegratedModeConfiguration="false" />
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" />
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" />
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" path="*." verb="GET,
        HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" 
        30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,
        bitness32" responseBufferLimit="0" />
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" path="*." verb="GET,
        HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" 
        30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,
        bitness64" responseBufferLimit="0" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="GET,
        HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" type="System.Web.Handlers.
        TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" 
      <!-- register HttpHandler used for BotDetect Captcha requests -->
      <remove name="BotDetectCaptchaHandler"/>
      <add name="BotDetectCaptchaHandler" preCondition="integratedMode" 
        verb="GET" path="BotDetectCaptcha.ashx" 
        type="BotDetect.Web.CaptchaHandler, BotDetect"/>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <assemblyIdentity name="System.Web.Mvc" 
          publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
      <helpLink enabled="true" mode="image" />

To allow the application to use BotDetect Captcha protection, we must enable and configure sessionState, and register the BotDetect HttpHandler in both <system.web><httpHandlers> and <system.webServer><handlers> configuration sections.

The <dependentAssembly> entry for System.Web.Mvc is also needed to make all ASP.NET MVC dependencies referenced by the BotDetect MVC assembly point to the correct ASP.NET MVC version.

Please Note

The information on this page is out of date and applies to a deprecated version of BotDetect™ CAPTCHA (v3.0).

An up-to-date equivalent page for the latest BotDetect Captcha release (v4) is BotDetect v4 Captcha documentation index.

General information about the major improvements in the current BotDetect release can be found at the What's New in BotDetect v4.0 page.