function BlockViewBuilder::preRender

#pre_render callback for building a block.

Renders the content using the provided block plugin, and then:

• if there is no content, aborts rendering, and makes sure the block won't be rendered.
• if there is content, moves the contextual links from the block content to the block itself.

File

core/modules/block/src/BlockViewBuilder.php, line 170

Class

BlockViewBuilder

Provides a Block view builder.

Namespace

Code

public static function preRender($build) {
    $content = $build['#block']->getPlugin()
        ->build();
    // Remove the block entity from the render array, to ensure that blocks
    // can be rendered without the block config entity.
    unset($build['#block']);
    if ($content !== NULL && !Element::isEmpty($content)) {
        // Place the $content returned by the block plugin into a 'content' child
        // element, as a way to allow the plugin to have complete control of its
        // properties and rendering (for instance, its own #theme) without
        // conflicting with the properties used above, or alternate ones used by
        // alternate block rendering approaches in contrib (for instance, Panels).
        // However, the use of a child element is an implementation detail of this
        // particular block rendering approach. Semantically, the content returned
        // by the plugin "is the" block, and in particular, #attributes and
        // #contextual_links is information about the *entire* block. Therefore,
        // we must move these properties from $content and merge them into the
        // top-level element.
        foreach ([
            '#attributes',
            '#contextual_links',
        ] as $property) {
            if (isset($content[$property])) {
                $build[$property] += $content[$property];
                unset($content[$property]);
            }
        }
        $build['content'] = $content;
    }
    else {
        // Abort rendering: render as the empty string and ensure this block is
        // render cached, so we can avoid the work of having to repeatedly
        // determine whether the block is empty. For instance, modifying or adding
        // entities could cause the block to no longer be empty.
        $build = [
            '#markup' => '',
            '#cache' => $build['#cache'],
        ];
        // If $content is not empty, then it contains cacheability metadata, and
        // we must merge it with the existing cacheability metadata. This allows
        // blocks to be empty, yet still bubble cacheability metadata, to indicate
        // why they are empty.
        if (!empty($content)) {
            CacheableMetadata::createFromRenderArray($build)->merge(CacheableMetadata::createFromRenderArray($content))
                ->applyTo($build);
        }
    }
    return $build;
}