Custom Form Handlers

Platformus.Forms extension offers the great forms features. You can describe your forms in the backend, and then render them and get user feedback on any frontend view. When user fills the form and clicks the Submit button, data is sent to a server and might be processed in any way you want. User input is handled by the implementations of the IFormHandler interface.

The selected implementation gets the form object, all the user input (string values by field objects), and all the attachments user has uploaded. It can return any IActionResult as the result.

Platformus has the only one built-in implementation of the IFormHandler interface: the EmailFormHandler class. It sends the user input to the specified email recipients.

Let’s implement our own form handler, which will just display the user input. Create the DisplayUserInputFormHandler class inside the main web application project and implement the IFormHandler interface there (in order to be able to write custom code in your Platformus-based web application, you can’t use Platformus as the compiled executable; use it as the NuGet packages instead, or write your own extension project and then put its compiled DLL file inside the extensions folder):

public class DisplayUserInputFormHandler : FormHandlerBase
  protected override IActionResult GetActionResult(IRequestHandler requestHandler, Form form, IDictionary<Field, string> valuesByFields, IDictionary<string, byte[]> attachmentsByFilenames)
    StringBuilder body = new StringBuilder();

    foreach (KeyValuePair<Field, string> valueByField in valuesByFields)
      body.AppendFormat("<p>{0}: {1}</p>", requestHandler.GetLocalizationValue(valueByField.Key.NameId), valueByField.Value);

    return (requestHandler as Controller).Content(body.ToString());

As you can see, we used the FormHandlerBase abstract class instead of implementing the IFormHandler interface from scratch. It provides useful methods to manipulate the form handler parameters (see below).

Now, when our form handler class is added, navigate to the backend’s Content/Forms section and create or edit a form:


Please note, that our new form handler C# class is automatically resolved and added to the drop down list. Click the Save button.

Now navigate to /en/contacts and fill out the form:


Click the Send button. Output from our form handler is displayed:


We could return some view, redirect, or any other action result we need.

Form Handler Parameters and Parameter Groups

As well as the endpoints and data sources, form handlers support parameters and parameter groups. The implementation is absolutely the same, so please just take a look at the one for the endpoints. Also, please take a look at the built-in form handler to see how it uses this feature.