Getting Started with the Captcha

This tutorial explains how to set up a basic Telerik UI for ASP.NET Core Captcha and highlights the major steps in the configuration of the component.

You will initialize a Captcha and learn how to add audio reading support. Then, you will see how to attach an event handler to the component. Finally, you can run the sample code in Telerik REPL and continue exploring the component.

Prerequisites

To successfully complete the tutorial, you need a project that is already configured to use the Telerik UI for ASP.NET Core components:

• You can use the Telerik REPL playground and skip installing the components on your system and configuring a project.

• You can prepare a Visual Studio project by following either of these guides:

  • Creating a new pre-configured project for the Telerik UI for ASP.NET Core components from a project template.

  • Manually configuring an existing project as described in the First Steps on Windows or First Steps on Mac articles.

1. Prepare the CSHTML File

The first step is to add the required directives at the top of the .cshtml document:

• To use the Telerik UI for ASP.NET Core HtmlHelpers:

  @using Kendo.Mvc.UI
  

• To use the Telerik UI for ASP.NET Core TagHelpers:

  @addTagHelper *, Kendo.Mvc
  

Optionally, you can structure the document by adding the desired HTML elements like headings, divs, paragraphs, and others.

@using Kendo.Mvc.UI

<h4>Captcha with event handler</h4>

<p>

</p>

@addTagHelper *, Kendo.Mvc

<h4>Captcha with event handler</h4>

<p>

</p>

2. Initialize the Captcha

Use the Captcha HtmlHelper or TagHelper to add the component to a page:

• The Name() configuration method is mandatory as its value is used for the id and the name attributes of the Captcha element.
• The DataCaptchaField() represents the main field.
• The DataCaptchaIdField() represents the ID field.
• The Handler() configuration points to the respective Controller action.

@using Kendo.Mvc.UI

<h4>Captcha with event handler</h4>

<p>
  @(Html.Kendo().Captcha()
   .Name("captcha")
   .DataCaptchaField("Captcha")
   .DataCaptchaIdField("CaptchaID")
   .Handler(handler => handler.Action("Reset_Events", "captcha"))
)
</p>

@addTagHelper *, Kendo.Mvc

<h4>Captcha with event handler</h4>

<p>
   <kendo-captcha name="captcha" 
    datacaptchafield="Captcha"
    datacaptchaidfield="CaptchaID">
      <handler url="@Url.Action("Reset_Events", "captcha")" />
   </kendo-captcha>
</p>

3. Add Audio Reader

The next step is to configure the Captcha to allow audio capability. You can do that by using the AudioHandlerFunction() configuration.

@using Kendo.Mvc.UI

<h4>Captcha with event handler</h4>

<script>
function audioHandler(args) {
    args.success("../shared/UserFiles/captcha/" + args.data.CaptchaID + ".wav");
}
</script>

<p>
  @(Html.Kendo().Captcha()
   .Name("captcha")
   .DataCaptchaField("Captcha")
   .DataCaptchaIdField("CaptchaID")
   .Handler(handler => handler.Action("Reset_Events", "captcha"))
   .AudioHandlerFunction("audioHandler")
)
</p>

@addTagHelper *, Kendo.Mvc

<h4>Captcha with event handler</h4>

<script>
function audioHandler(args) {
    args.success("../shared/UserFiles/captcha/" + args.data.CaptchaID + ".wav");
}
</script>

<p>
   <kendo-captcha name="captcha" 
    datacaptchafield="Captcha"
    datacaptchaidfield="CaptchaID">
      <handler url="@Url.Action("Reset_Events", "captcha")" />
         <audio-handler function-handler="audioHandler" />
   </kendo-captcha>
</p>

4. Handle a Captcha Event

The Captcha exposes a Change() event that you can handle and assign specific functions to the component. In this tutorial, you will use the Change() event to display a message when the user changes the input value.

@using Kendo.Mvc.UI

<h4>Captcha with event handler</h4>

<script>
function audioHandler(args) {
    args.success("../shared/UserFiles/captcha/" + args.data.CaptchaID + ".wav");
}
function onChange(e) {
    var value = e.sender.value();
    console.log(value);
}
</script>

<p>
  @(Html.Kendo().Captcha()
   .Name("captcha")
   .DataCaptchaField("Captcha")
   .DataCaptchaIdField("CaptchaID")
   .Handler(handler => handler.Action("Reset_Events", "captcha"))
   .AudioHandlerFunction("audioHandler")
   .Events(e => e.Change("onChange"))
)
</p>

@addTagHelper *, Kendo.Mvc

<h4>Captcha with event handler</h4>

<script>
function audioHandler(args) {
    args.success("../shared/UserFiles/captcha/" + args.data.CaptchaID + ".wav");
}
function onChange(e) {
    var value = e.sender.value();
    console.log(value);
}
</script>

<p>
   <kendo-captcha name="captcha" 
    datacaptchafield="Captcha"
    datacaptchaidfield="CaptchaID"
    on-change="onChange">
      <handler url="@Url.Action("Reset_Events", "captcha")" />
         <audio-handler function-handler="audioHandler" />
   </kendo-captcha>
</p>

For more examples, refer to the demo on using the events of the Captcha.

5. (Optional) Reference Existing Captcha Instances

You can reference the Captcha instances that you have created and build on top of their existing configuration:

1. Use the id attribute of the component instance to establish a reference.

   <script>
       var captchaReference = $("#captcha").data("kendoCaptcha"); // captchaReference is a reference to the existing captcha instance of the helper.
   </script>
   

2. Use the Captcha client-side API to control the behavior of the widget. In this example, you will use the reset method to refresh the captcha.

   <script>
       var captchaReference = $("#captcha").data("kendoCaptcha"); // captchaReference is a reference to the existing timeCaptcha instance of the helper.
        captchaReference.reset(); // refreshes the Captcha
   </script>
   

For more information on referencing specific helper instances, see the Methods and Events article.

Explore this Tutorial in REPL

You can continue experimenting with the code sample above by running it in the Telerik REPL server playground:

• Sample code with the Captcha HtmlHelper
• Sample code with the Captcha TagHelper

Next Steps

• Configure the Provider of the Captcha
• Configure the Captcha's Validation

See Also

• Using the API of the Captcha for ASP.NET Core (Demo)
• Client-Side API of the Captcha
• Server-Side API of the Captcha
• Knowledge Base Section