SimplePageVariant.php

<?php

namespace Drupal\Core\Render\Plugin\DisplayVariant;

use Drupal\Core\Display\PageVariantInterface;
use Drupal\Core\Display\VariantBase;

/**
 * Provides a page display variant that simply renders the main content.
 *
 * @PageDisplayVariant(
 *   id = "simple_page",
 *   admin_label = @Translation("Simple page")
 * )
 */
class SimplePageVariant extends VariantBase implements PageVariantInterface {
    
    /**
     * The render array representing the main content.
     *
     * @var array
     */
    protected $mainContent;
    
    /**
     * The page title: a string (plain title) or a render array (formatted title).
     *
     * @var string|array
     */
    protected $title = '';
    
    /**
     * {@inheritdoc}
     */
    public function setMainContent(array $main_content) {
        $this->mainContent = $main_content;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setTitle($title) {
        $this->title = $title;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function build() {
        $build = [
            'content' => [
                'messages' => [
                    '#type' => 'status_messages',
                    '#weight' => -1000,
                    '#include_fallback' => TRUE,
                ],
                'page_title' => [
                    '#type' => 'page_title',
                    '#title' => $this->title,
                    '#weight' => -900,
                ],
                'main_content' => [
                    '#weight' => -800,
                ] + $this->mainContent,
            ],
        ];
        return $build;
    }

}