setMainContent example

      }

      $title = $get_title($main_content);

      // Instantiate the page display, and give it the main content.       $page_display = $this->displayVariantManager->createInstance($variant_id, $variant_configuration);
      if (!$page_display instanceof PageVariantInterface) {
        throw new \LogicException('Cannot render the main content for this page because the provided display variant does not implement PageVariantInterface.');
      }
      $page_display
        ->setMainContent($main_content)
        ->setTitle($title)
        ->addCacheableDependency($event);
      // Some display variants need to be passed an array of contexts with       // values because they can't get all their contexts globally. For example,       // in Page Manager, you can create a Page which has a specific static       // context (e.g. a context that refers to the Node with nid 6), if any       // such contexts were added to the $event, pass them to the $page_display.       if ($page_display instanceof ContextAwareVariantInterface) {
        $page_display->setContexts($event->getContexts());
      }

      

  /** * Tests the building of a full page variant. * * @covers ::build * * @dataProvider providerBuild */
  public function testBuild(array $blocks_config, $visible_block_count, array $expected_render_array) {
    $display_variant = $this->setUpDisplayVariant();
    $display_variant->setMainContent(['#markup' => 'Hello kittens!']);

    $blocks = ['top' => [], 'center' => [], 'bottom' => []];
    $block_plugin = $this->createMock('Drupal\Core\Block\BlockPluginInterface');
    $main_content_block_plugin = $this->createMock('Drupal\Core\Block\MainContentBlockPluginInterface');
    $messages_block_plugin = $this->createMock('Drupal\Core\Block\MessagesBlockPluginInterface');
    $title_block_plugin = $this->createMock('Drupal\Core\Block\TitleBlockPluginInterface');
    foreach ($blocks_config as $block_id => $block_config) {
      $block = $this->createMock('Drupal\block\BlockInterface');
      $block->expects($this->atLeastOnce())
        ->method('getPlugin')
        ->willReturn($block_config[1] ? $main_content_block_plugin : ($block_config[2] ? $messages_block_plugin : ($block_config[3] ? $title_block_plugin : $block_plugin)));
      

'#cache' => [
        'tags' => $this->blockListCacheTags,
      ],
    ];
    // Load all region content assigned via blocks.     $cacheable_metadata_list = [];
    foreach ($this->blockRepository->getVisibleBlocksPerRegion($cacheable_metadata_list) as $region => $blocks) {
      /** @var \Drupal\block\BlockInterface[] $blocks */
      foreach ($blocks as $key => $block) {
        $block_plugin = $block->getPlugin();
        if ($block_plugin instanceof MainContentBlockPluginInterface) {
          $block_plugin->setMainContent($this->mainContent);
          $main_content_block_displayed = TRUE;
        }
        elseif ($block_plugin instanceof TitleBlockPluginInterface) {
          $block_plugin->setTitle($this->title);
        }
        elseif ($block_plugin instanceof MessagesBlockPluginInterface) {
          $messages_block_displayed = TRUE;
        }
        $build[$region][$key] = $this->blockViewBuilder->view($block);

        // The main content block cannot be cached: it is a placeholder for the