Drupal 8 Third Party Settings and Pseudo-Fields

This Drupal 8 module creates reusable forms that can be attached to different node bundles. Let's build a simple, yet powerful, reusable form system. The goal is to easily load a form on each node page, selecting the form type per node bundle.

We've already created a custom plugin type, ReusableForm, with a base plugin class for extension. Each plugin interacts with a form class defined in its annotation. Similarly, a base form class provides a foundation for new forms.

Next, we'll configure core node types to utilize these plugins and render the appropriate form during node display. First, let's create a simple ReusableForm plugin.

Key Concepts:

• ReusableForm Plugin: A custom plugin type allowing selection of forms per node bundle.
• Form Class: Defines the structure and logic of each individual form.
• Plugin Manager Service: Provides access to available ReusableForm plugins.
• Third-Party Settings: Stores plugin selection per node type.
• Pseudo Field: Allows rendering the selected form on the node display.

Creating the First Plugin

In the module's src/Form directory, create BasicForm.php:

<?php
namespace Drupal\reusable_forms\Form;

use Drupal\Core\Form\FormStateInterface;

class BasicForm extends ReusableFormBase {

  public function getFormId() {
    return 'basic_form';
  }

  public function buildForm(array $form, FormStateInterface $form_state) {
    $form = parent::buildForm($form, $form_state);
    return $form;
  }

  public function submitForm(array &$form, FormStateInterface $form_state) {
    // Handle form submission.
  }
}

This extends our base form, implementing required methods. The buildForm method utilizes the base class logic. Submission handling is left for later implementation.

Now, create the plugin in src/Plugin/ReusableForm/BasicForm.php:

<?php
namespace Drupal\reusable_forms\Plugin\ReusableForm;

use Drupal\reusable_forms\ReusableFormPluginBase;

/**
 * @ReusableForm(
 *   id = "basic_form",
 *   name = @Translation("Basic Form"),
 *   form = "Drupal\reusable_forms\Form\BasicForm"
 * )
 */
class BasicForm extends ReusableFormPluginBase {}

The annotation defines the plugin's ID, name, and associated form class.

Node Type Configuration

To access and load plugins, we'll make the plugin manager a service. In reusable_forms.services.yml:

services:
  plugin.manager.reusable_forms:
    class: Drupal\reusable_forms\ReusableFormsManager
    parent: default_plugin_manager

Next, alter the node type edit form (reusable_forms.module):

use Drupal\Core\Form\FormStateInterface;
use Drupal\node\NodeTypeInterface;

function reusable_forms_form_node_type_form_alter(&$form, FormStateInterface $form_state) {
  // ... (Code to add checkbox and radios for enabling and selecting forms) ...
  $form['#entity_builders'][] = 'reusable_forms_form_node_type_form_builder';
}

function reusable_forms_form_node_type_form_builder($entity_type, NodeTypeInterface $type, &$form, FormStateInterface $form_state) {
  // ... (Code to save/unset third-party settings) ...
}

This adds a checkbox to enable reusable forms and a select list to choose a plugin. The #entity_builders callback saves the selection in third-party settings.

Configuration Schema (reusable_forms.schema.yml)

node.type.*.third_party.reusable_forms:
  type: mapping
  label: 'Reusable Forms'
  mapping:
    enabled:
      type: boolean
      label: 'Enable reusable forms'
    plugin:
      type: string
      label: 'Form Plugin'

Node View

Create a pseudo field (reusable_forms.module):

use Drupal\node\Entity\NodeType;
use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
use Drupal\Core\Entity\EntityInterface;

function reusable_forms_entity_extra_field_info() {
  // ... (Code to add 'reusable_form' pseudo field to enabled node types) ...
}

function reusable_forms_node_view(array &$build, EntityInterface $entity, EntityViewDisplayInterface $display, $view_mode, $langcode) {
  // ... (Code to render the form using the plugin manager) ...
}

hook_entity_extra_field_info defines the pseudo field, and hook_node_view renders the selected form.

This completes the basic structure. Remember to clear caches after making changes. This detailed explanation provides a solid foundation for building more complex reusable form functionality in Drupal 8.

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