How to add a new custom field to "Site Infomation" Form in Drupal8

Question

I want to Add a new custom field to "Site Infomation" Form in Drupal8. I have tried many answers but didnt get the proper solution. Is there any way to add custom field. Please suggest. Thanx in advance.

Answer 1

Consider module name is mymodule.

Example of a mymodule.services.yml file

Register an Event Subscriber in your mymodule.services.yml

services:
  bssa.route_subscriber:
    class: Drupal\bssa\Routing\RouteSubscriber
    tags:
      - { name: event_subscriber }

class : "Drupal\\mymodule\\Routing\\RouteSubscriber" According to this class create a php file as given below.

Extend the RouteSubscriber to implement the new field form as mymodule/src/Routing/RouteSubscriber.php

<?php 
namespace Drupal\mymodule\Routing;

use Drupal\Core\Routing\RouteSubscriberBase;
use Symfony\Component\Routing\RouteCollection;

/**
 * Listens to the dynamic route events.
 */
class RouteSubscriber extends RouteSubscriberBase {

  /**
   * {@inheritdoc}
   */
  protected function alterRoutes(RouteCollection $collection) {
    if ($route = $collection->get('system.site_information_settings')) 
      $route->setDefault('_form', 'Drupal\mymodule\Form\ExtendedSiteInformationForm');
  }

}

Now create a new form in mymodule/src/Form/ExtendedSiteInformation.php to add the custom field

<?php

namespace Drupal\mymodule\Form;

use Drupal\Core\Form\FormStateInterface;
use Drupal\system\Form\SiteInformationForm;


class ExtendedSiteInformationForm extends SiteInformationForm {

   /**
   * {@inheritdoc}
   */
      public function buildForm(array $form, FormStateInterface $form_state) {
        $site_config = $this->config('system.site');
        $form =  parent::buildForm($form, $form_state);
        $form['site_information']['siteapikey'] = [
            '#type' => 'textfield',
            '#title' => t('Site API Key'),
            '#default_value' => $site_config->get('siteapikey') ?: 'No API Key yet',
            '#description' => t("Custom field to set the API Key"),
        ];

        return $form;
    }

      public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->config('system.site')
          ->set('siteapikey', $form_state->getValue('siteapikey'))
          ->save();
        parent::submitForm($form, $form_state);
      }
}

Now create a config variable to hold the value of the new field inside mymodule/config/schema/mymodule.schema.yml

# We want to extend the system.site configuration
system.site:
  mapping:
    # Our field name is 'siteapikey'
    siteapikey:
      type: label
      label: 'Site API Keys'

After follow the above steps clear the cache and you will see a new field "Site API Key" in the "Site Information" Form.