ThemingPageController.php

<?php

namespace Drupal\theming_example\Controller;

use Drupal\Core\StringTranslation\StringTranslationTrait;
use Drupal\Core\Url;

/**
 *
 */
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 a #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,
        // theme('theming_example_list').
        $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;
    }

}