ReorderDisplays::submitForm

public ReorderDisplays::submitForm(array &$form, FormStateInterface $form_state)

public function submitForm(array &$form, FormStateInterface $form_state) {
  /** @var $view \Drupal\views_ui\ViewUI */
  $view = $form_state->get('view');
  $order = array();

  $user_input = $form_state->getUserInput();
  foreach ($user_input['displays'] as $display => $info) {
    // Add each value that is a field with a weight to our list, but only if
    // it has had its 'removed' checkbox checked.
    if (is_array($info) && isset($info['weight']) && empty($info['removed']['checkbox'])) {
      $order[$display] = $info['weight'];
    }
  }

  // Sort the order array.
  asort($order);

  // Remove the default display from ordering.
  unset($order['default']);
  // Increment up positions.
  $position = 1;

  foreach (array_keys($order) as $display) {
    $order[$display] = $position++;
  }

  // Setting up position and removing deleted displays.
  $displays = $view->get('display');
  foreach ($displays as $display_id => &$display) {
    // Don't touch the default.
    if ($display_id === 'default') {
      $display['position'] = 0;
      continue;
    }
    if (isset($order[$display_id])) {
      $display['position'] = $order[$display_id];
    }
    else {
      $display['deleted'] = TRUE;
    }
  }
  $view->set('display', $displays);

  // Store in cache.
  $view->cacheSet();
  $url = $view->urlInfo('edit-form')
    ->setOption('fragment', 'views-tab-default');
  $form_state->setRedirectUrl($url);
}