Define block in Drupal module

Part V of the Practical Guide to Creating Basic Drupal 8 Modules
From .info to tests, just the basics

Remember at the beginning of this tutorial I mentioned we’d define a block with a form? Well, now is the time to dive into it.

/src/Form/LoremIpsumBlockForm.php

<?php

namespace Drupal\loremipsum\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Url;

/**
 * Lorem Ipsum block form
 */
class LoremIpsumBlockForm extends FormBase {

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'loremipsum_block_form';
  }

This file is very similar to a configuration form file, except that it extends the FormBase class.

It also has a buildForm() method that looks like this:

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $options = array_combine(range(1, 10), range(1, 10));
    $form['paragraphs'] = [
      '#type' => 'select',
      '#title' => $this->t('Paragraphs'),
      '#options' => $options,
      '#default_value' => 4,
      '#description' => $this->t('How many?'),
    ];

    $form['phrases'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Phrases'),
      '#default_value' => '20',
      '#description' => $this->t('Maximum per paragraph'),
    ];

    $form['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Generate'),
    ];

    return $form;
  }

This method is used to place the form in a block, allowing users to configure how much dummy text they want to generate.

Also, don’t forget the validateForm() and submitForm() methods:

  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    $phrases = $form_state->getValue('phrases');
    if (!is_numeric($phrases)) {
      $form_state->setErrorByName('phrases', $this->t('Please use a number.'));
    }

    if (floor($phrases) != $phrases) {
      $form_state->setErrorByName('phrases', $this->t('No decimals, please.'));
    }

    if ($phrases  1) {
      $form_state->setErrorByName('phrases', $this->t('Please use a number greater than zero.'));
    }
  }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $form_state->setRedirect('loremipsum.generate', [
      'paragraphs' => $form_state->getValue('paragraphs'),
      'phrases' => $form_state->getValue('phrases'),
    ]);
  }

}

Now for the actual block class:

<?php

namespace Drupal\loremipsum\Plugin\Block;

use Drupal\Core\Access\AccessResult;
use Drupal\Core\Block\BlockBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Session\AccountInterface;

/**
 * Provides a Lorem ipsum block with which you can generate dummy text anywhere.
 *
 * @Block(
 *   id = "loremipsum_block",
 *   admin_label = @Translation("Lorem ipsum block"),
 * )
 */
class LoremIpsumBlock extends BlockBase {

  /**
   * {@inheritdoc}
   */
  public function build() {
    return \Drupal::formBuilder()->getForm('Drupal\loremipsum\Form\LoremIpsumBlockForm');
  }

The LoremIpsumBlock class extends BlockBase and includes four key methods: build(), blockAccess(), blockForm(), and blockSubmit(). The first simply renders the form defined in the previous step.

Next, we handle access control:

  /**
   * {@inheritdoc}
   */
  protected function blockAccess(AccountInterface $account) {
    return AccessResult::allowedIfHasPermission($account, 'generate lorem ipsum');
  }

Define a block configuration form for the block admin UI:

  /**
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state) {
    $form = parent::blockForm($form, $form_state);

    $config = $this->getConfiguration();

    return $form;
  }

And the submit handler:

  /**
   * {@inheritdoc}
   */
  public function blockSubmit($form, FormStateInterface $form_state) {
    $this->setConfigurationValue('loremipsum_block_settings', $form_state->getValue('loremipsum_block_settings'));
  }

}

Now your block should be functional.