class SimplePageVariant

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;
  }

}