Implement D3 Example In Drupal 8

It will provide us a base class for forms. This class exists as a mid-point between dependency injection through ContainerInjectionInterface, as well as a less-structured use of traits which default to using the \Drupal accessor for service discovery. To properly inject this services, override create() and use the setters provided by the traits to inject the needed services.

public static function create($container) {
  $form = new static();
  // In this example we only need string translation so we use the
  // setStringTranslation() method provided by StringTranslationTrait.
  $form->setStringTranslation($container->get('string_translation'));
  return $form;
}

Alternately, please do not use FormBase. A class can implement FormInterface, use the traits it needs, and inject services from the container as required.

It will provide an interface for an object containing the current state of a form. This is passed to all form related code so that the caller can use it to examine what in the form changed when the form submission process is complete. Furthermore, it may be used to store information related to the processed data in the form, which will persist across page requests when the ‘cache’ or ‘rebuild’ flag is set. Please do check the link \Drupal\Core\Form\FormState::$internalStorage for documentation of the available flags.

It will defines an object that holds information about a URL. This module has main view which is showing select option that is actually created by FormBase controller buildForm function Drupal\Core\Form\FormBase and Drupal\Core\Form\FormStateInterface. When User select any option from selection and submit the form on submit FormBase controller submitForm function call. (Drupal\Core\Form\FormBase and Drupal\Core\Form\FormStateInterface). On submit we have use
$form_state->setRedirect

to redirect user to selected D3 view.

To view D3 selected view, we have used switch case for get parameter from url.
This switch case depend url parameter and call template and libraries by using ‘#theme’ and ‘#markup’ element of drupal 8. The element ‘#theme’ call templates of module by calling theme hook. In templates folder, *.html.twig files contain html and libraries. It can be attached from Twig templates via an attach_library() function. This all Different process renders the view of D3 JS.