class ThemingPageController

class ThemingPageController {
  use StringTranslationTrait;
  
  /**
   * Initial landing page explaining the use of the module.
   *
   * We create a render array and specify the theme to be used through the use
   * of #theme_wrappers. With all output, we aim to leave the content as a
   * render array just as long as possible, so that other modules (or the theme)
   * can alter it.
   *
   * @see render_example.module
   * @see form_example_elements.inc
   */
  public function entryPage() {
    $links = [];
    $links[] = [
      '#type' => 'link',
      '#url' => Url::fromRoute('theming_example.list'),
      '#title' => $this->t('Simple page with a list'),
    ];
    $links[] = [
      '#type' => 'link',
      '#url' => Url::fromRoute('theming_example.form_select'),
      '#title' => $this->t('Simple form 1'),
    ];
    $links[] = [
      '#type' => 'link',
      '#url' => Url::fromRoute('theming_example.form_text'),
      '#title' => $this->t('Simple form 2'),
    ];
    $content = [
      '#theme' => 'item_list',
      '#theme_wrappers' => [
        'theming_example_content_array',
      ],
      '#items' => $links,
      '#title' => $this->t('Some examples of pages and forms that are run through theme functions.'),
    ];
    return $content;
  }
  
  /**
   * The list page callback.
   *
   * An example page where the output is supplied as an array which is themed
   * into a list and styled with css.
   *
   * In this case we'll use the core-provided theme_item_list as #theme_wrapper.
   * Any theme need only override theme_item_list to change the behavior.
   */
  public function list() {
    $items = [
      $this->t('First item'),
      $this->t('Second item'),
      $this->t('Third item'),
      $this->t('Fourth item'),
    ];
    // First we'll create a render array that simply uses theme_item_list.
    $title = $this->t("A list returned to be rendered using theme('item_list')");
    $build['render_version'] = [
      // We use #theme here instead of #theme_wrappers because theme_item_list()
      // is the classic type of theme function that does not just assume a
      // render array, but instead has its own properties
      // (#type, #title, #items).
'#theme' => 'item_list',
      // '#type' => 'ul',  // The default type is 'ul'
      // We can easily make sure that a css or js file is present using
      // #attached.
'#attached' => [
        'library' => [
          'theming_example/list',
        ],
      ],
      '#title' => $title,
      '#items' => $items,
      '#attributes' => [
        'class' => [
          'render-version-list',
        ],
      ],
    ];
    // Now we'll create a render array which uses our own list formatter.
    $title = $this->t("The same list rendered by theme('theming_example_list')");
    $build['our_theme_function'] = [
      '#theme' => 'theming_example_list',
      '#attached' => [
        'library' => [
          'theming_example/list',
        ],
      ],
      '#title' => $title,
      '#items' => $items,
    ];
    return $build;
  }

}