How to create a custom block in Drupal 8?

@larissa 

To create a custom block in Drupal 8, you can use one of the following methods:

1. Use the Drupal Console to generate a block plugin:

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drupal generate:plugin:block

1. Create a block plugin manually:

• Create a folder for your custom module, if it doesn't already exist.
• Create a src folder in your custom module folder.
• Create a Plugin folder in the src folder.
• Create a Block folder in the Plugin folder.
• Create a PHP file for your custom block in the Block folder. The file name should follow the pattern {BLOCK_NAME}Block.php.
• Define your custom block class in the PHP file. The class should extend the BlockBase class and implement the BlockPluginInterface interface.
• Annotate the block class with @Block annotation.
• Implement the build() method, which should return the content (formatted as a render array) that you want to display in the block.

Here is an example of a custom block class:

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<?php

namespace DrupalmymodulePluginBlock;

use DrupalCoreBlockBlockBase;
use DrupalCoreBlockBlockPluginInterface;
use DrupalCoreFormFormStateInterface;

/**
 * Provides a 'MyCustomBlock' block.
 *
 * @Block(
 *   id = "mycustom_block",
 *   admin_label = @Translation("My custom block"),
 *   category = @Translation("Custom"),
 * )
 */
class MyCustomBlock extends BlockBase implements BlockPluginInterface {

  /**
   * {@inheritdoc}
   */
  public function build() {
    $build = [];
    $build['mycustom_block']['#markup'] = 'Hello World!';

    return $build;
  }

}

1. Use the Drupal user interface to create a custom block:

• Go to the "Structure" menu and click on the "Block layout" link.
• Click on the "Place block" button for the region where you want to add the custom block.
• In the "Add custom block" section, enter a name and a description for your custom block.
• In the "Block body" field, enter the content that you want to display in the block.
• Click on the "Save block" button.

I hope this helps! Let me know if you have any further questions.