ASP.NET MVC 5.0 Basic CAPTCHA VB.NET Code Sample (BotDetect v3.0; deprecated)

The ASP.NET MVC 5.0 Basic Captcha VB.NET 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.vbhtml, 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

Installed Location

By default, the .NET 4.5 VB.NET version of the ASP.NET MVC 5.0 Basic Captcha sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v4.5\WebApp\AspNetMvc50BasicCaptchaSample\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


@* namespaces needed to access BotDetect members *@
@Imports BotDetect.Web.UI.Mvc

    Layout = Nothing
End Code

<!DOCTYPE html>

<head runat="server">
    <meta name="viewport" content="width=device-width" />
    <title>BotDetect ASP.NET MVC 5.0 Basic CAPTCHA Sample VB.NET</title>
    <link href="@Url.Content("~/Style/Sheet.css")" rel="stylesheet" type="text/css" />
    <link href="@BotDetect.Web.CaptchaUrls.Absolute.LayoutStyleSheetUrl" 
      rel="stylesheet" type="text/css" />
    <h1>BotDetect ASP.NET MVC 5.0 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:")
                @Code Dim sampleCaptcha As MvcCaptcha = _
                  New MvcCaptcha("SampleCaptcha")
                      sampleCaptcha.UserInputClientID = "CaptchaCode" End Code
            <div class="actions">
                <input type="submit" value="Validate" />
                @If ((Request.HttpMethod = "POST") And ViewData.ModelState.IsValid) _ 
                     @<span class="correct">Correct!</span>
                End If
    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 AspNetMvc50BasicCaptchaSampleVBNet
    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!")> _
        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 visit
    <section name="botDetect" requirePermission="false" 
      type="BotDetect.Configuration.BotDetectConfigurationSection, BotDetect"/>
    <add key="webpages:Version" value=""/>
    <add key="webpages:Enabled" value="false"/>
    <add key="ClientValidationEnabled" value="false"/>
    <add key="UnobtrusiveJavaScriptEnabled" value="false"/>
    <compilation debug="false" targetFramework="4.5.1"/>
    <httpRuntime targetFramework="4.5.1"/>
    <!-- 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" />
      <!-- 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.Helpers" publicKeyToken="31bf3856ad364e35"/>
        <bindingRedirect oldVersion="" newVersion=""/>
        <assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35"/>
        <bindingRedirect oldVersion="" newVersion=""/>
        <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 register the BotDetect HttpHandler in both <system.web><httpHandlers> and <system.webServer><handlers> configuration sections, and enable and configure ASP.NET sessionState.

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.