Create Flex Object with FE Form

  form:
    name: contact
    fields:
      published:
        type: toggle
        label: PLUGIN_ADMIN.ENABLED
        highlight: 1
        help: PLUGIN_ADMIN.ENABLED_HELP
        options:
          1: PLUGIN_ADMIN.YES
          0: PLUGIN_ADMIN.NO
        validate:
          type: bool
      first_name: 
        type: text
        validate:
          required: true
      last_name:
        type: text
        validate:
          required: true
      email:
        type: email
        validate:
          required: true
      website:
        type: text
        validate:
          required: true
      tags:
        type: select
        multiple: true
        options:
          Red: Red
          Blue: Blue
          Green: Green
          White: White
          Black: Black
          Pink: Pink
          Violet: Violet
        validate:
          type: array

    buttons:
      submit:
        type: submit
    process:
      - addContact:
      - reset: true

  <?php

  namespace Grav\Plugin;

  use Composer\Autoload\ClassLoader;
  use Grav\Common\Grav;
  use Grav\Common\Plugin;
  use Grav\Framework\Flex\Interfaces\FlexDirectoryInterface;
  use Grav\Framework\Flex\Interfaces\FlexObjectInterface;
  use Grav\Plugin\Form\Form;
  use RocketTheme\Toolbox\Event\Event;

  /**
   * Class ContactPlugin
   * @package Grav\Plugin
   */
  class ContactPlugin extends Plugin
  {
    /**
     * @return array
     *
     * The getSubscribedEvents() gives the core a list of events
     *     that the plugin wants to listen to. The key of each
     *     array section is the event that the plugin listens to
     *     and the value (in the form of an array) contains the
     *     callable (or function) as well as the priority. The
     *     higher the number the higher the priority.
     */
    public static function getSubscribedEvents(): array
    {
      return [
        'onPluginsInitialized' => [
          // Uncomment following line when plugin requires Grav < 1.7
          // ['autoload', 100000],
          ['onPluginsInitialized', 0]
        ]
      ];
    }

    /**
     * Composer autoload
     *
     * @return ClassLoader
     */
    public function autoload(): ClassLoader
    {
      return require __DIR__ . '/vendor/autoload.php';
    }

    /**
     * Initialize the plugin
     */
    public function onPluginsInitialized(): void
    {
      // Don't proceed if we are in the admin plugin
      if ($this->isAdmin()) {
        return;
      }

      // Enable the main events we are interested in
      $this->enable([
        // Put your main even'ts here
        'onFormProcessed' => ['onFormProcessed', 0],
      ]);
    }

    public function onFormProcessed(Event $event)
    {
      /** @var Form */
      $form = $event['form'];
      /** @var string */
      $action = $event['action'];

      switch ($action) {
        case 'addContact':
          /** @var FlexDirectoryInterface */
          $directory = Grav::instance()->get('flex')->getDirectory('contacts');

          /** @var FlexObjectInterface */
          $newObject = $directory->createObject([
            'published' =>  $form->value('published', true),
            'first_name' => $form->value('first_name'),
            'last_name' => $form->value('last_name'),
            'email' => $form->value('email'),
            'website' => $form->value('website'),
            'tags' => $form->value('tags', []),
          ]);

          $newObject->save();

          break;
        case 'otherAction':
          // ...
          break;
      }
    }
  }