ViewAddForm::form

public ViewAddForm::form(array $form, FormStateInterface $form_state)

public function form(array $form, FormStateInterface $form_state) {
  $form['#attached']['library'][] = 'views_ui/views_ui.admin';
  $form['#attributes']['class'] = array('views-admin');

  $form['name'] = array(
    '#type' => 'fieldset',
    '#title' => t('View basic information'),
    '#attributes' => array('class' => array('fieldset-no-legend')),
  );

  $form['name']['label'] = array(
    '#type' => 'textfield',
    '#title' => $this->t('View name'),
    '#required' => TRUE,
    '#size' => 32,
    '#default_value' => '',
    '#maxlength' => 255,
  );
  $form['name']['id'] = array(
    '#type' => 'machine_name',
    '#maxlength' => 128,
    '#machine_name' => array(
      'exists' => '\Drupal\views\Views::getView',
      'source' => array('name', 'label'),
    ),
    '#description' => $this->t('A unique machine-readable name for this View. It must only contain lowercase letters, numbers, and underscores.'),
  );

  $form['name']['description_enable'] = array(
    '#type' => 'checkbox',
    '#title' => $this->t('Description'),
  );
  $form['name']['description'] = array(
    '#type' => 'textfield',
    '#title' => $this->t('Provide description'),
    '#title_display' => 'invisible',
    '#size' => 64,
    '#default_value' => '',
    '#states' => array(
      'visible' => array(
        ':input[name="description_enable"]' => array('checked' => TRUE),
      ),
    ),
  );

  // Create a wrapper for the entire dynamic portion of the form. Everything
  // that can be updated by AJAX goes somewhere inside here. For example, this
  // is needed by "Show" dropdown (below); it changes the base table of the
  // view and therefore potentially requires all options on the form to be
  // dynamically updated.
  $form['displays'] = array();

  // Create the part of the form that allows the user to select the basic
  // properties of what the view will display.
  $form['displays']['show'] = array(
    '#type' => 'fieldset',
    '#title' => t('View settings'),
    '#tree' => TRUE,
    '#attributes' => array('class' => array('container-inline')),
  );

  // Create the "Show" dropdown, which allows the base table of the view to be
  // selected.
  $wizard_plugins = $this->wizardManager->getDefinitions();
  $options = array();
  foreach ($wizard_plugins as $key => $wizard) {
    $options[$key] = $wizard['title'];
  }
  $form['displays']['show']['wizard_key'] = array(
    '#type' => 'select',
    '#title' => $this->t('Show'),
    '#options' => $options,
  );
  $show_form = &$form['displays']['show'];
  $default_value = \Drupal::moduleHandler()->moduleExists('node') ? 'node' : 'users';
  $show_form['wizard_key']['#default_value'] = WizardPluginBase::getSelected($form_state, array('show', 'wizard_key'), $default_value, $show_form['wizard_key']);
  // Changing this dropdown updates the entire content of $form['displays'] via
  // AJAX.
  views_ui_add_ajax_trigger($show_form, 'wizard_key', array('displays'));

  // Build the rest of the form based on the currently selected wizard plugin.
  $wizard_key = $show_form['wizard_key']['#default_value'];
  $wizard_instance = $this->wizardManager->createInstance($wizard_key);
  $form = $wizard_instance->buildForm($form, $form_state);

  return $form;
}