block_example.module

<?php

/**
 * @file
 * Module file for block_example.
 */
use Drupal\Core\Block\BlockPluginInterface;

/**
 * @defgroup block_example Example: Block
 * @ingroup examples
 * @{
 * Demonstrates code creation of blocks.
 *
 * This example demonstrates how a module can define blocks that can be
 * displayed on various pages of a site, and how to alter blocks provided by
 * other modules.
 */

/**
 * Implements hook_block_view_alter().
 *
 * This hook allows you to modify the output of any block in the system.
 *
 * We are going to change the block label to uppercase if it contains the string
 * "uppercase" or if the default block label contains this string. The default
 * block label is set programmatically in the subject key of the block's plugin
 * definition. The configurable block label, which can be overridden through the
 * UI, is found in the "#configuration" key of the block's build definition.
 * This module creates a block that demonstrates the uppercase effect in the
 * "Example: uppercase this please" block. You can also demonstrate the effect
 * of this hook by editing the title of an existing block or by creating a new
 * block which where the default label has the string "uppercase" in it.
 *
 * Instead of hook_block_view_alter(), which is called for all blocks, you can
 * also use hook_block_view_BASE_BLOCK_ID_alter() to alter a specific block. To
 * only change the "example_uppercase" block we would use the function:
 * hook_block_view_example_uppercase_alter().
 */
function block_example_block_view_alter(array &$build, BlockPluginInterface $block) {

  // We'll search for the string 'uppercase'.
  $definition = $block
    ->getPluginDefinition();
  if (!empty($build['#configuration']['label']) && mb_strpos($build['#configuration']['label'], 'uppercase') || !empty($definition['subject']) && mb_strpos($definition['subject'], 'uppercase')) {

    // This will uppercase the block title.
    $build['#configuration']['label'] = mb_strtoupper($build['#configuration']['label']);
  }
}

/**
 * @} End of "defgroup block_example".
 */