D8 Database Queue Example

QueueExampleForm.php

<?php

namespace Drupal\queue_example\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Drupal\Core\Queue\QueueDatabaseFactory;

/**
 * Class QueueExampleForm.
 */
class QueueExample extends FormBase {

  const QUEUE_NAME = 'item_queue';

  protected $databaseQueue;

  /**
   * Get DatabaseQueue from factory.
   */
  public function __construct(QueueDatabaseFactory $queue_database) {
    $this->databaseQueue = $queue_database->get($this::QUEUE_NAME);
  }

  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('queue.database')
    );
  }

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

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $item_count = $this->databaseQueue->numberOfItems();
    $form['item_count'] = [
      '#type' => 'item',
      '#title' => $this->t('Item Count'),
      '#markup' => $this->databaseQueue->numberOfItems(),
    ];

    $form['new_item'] = [
      '#type' => 'textfield',
      '#title' => $this->t('New Item'),
    ];

    $form['add_item'] = [
      '#type' => 'submit',
      '#value' => $this->t('Add Item'),
      '#submit' => [[$this, 'submitAddItem']],
    ];

    $form['remove_item'] = [
      '#type' => 'submit',
      '#value' => $this->t('Remove Item'),
      '#submit' => [[$this, 'submitRemoveItem']],
    ];

    $form['clear_queue'] = [
      '#type' => 'submit',
      '#value' => $this->t('Clear Queue'),
    ];
    return $form;
  }

  /**
   * Add a queue item.
   */
  public function submitAddItem(array &$form, FormStateInterface $form_state) {
    $item = $form_state->getValue('new_item');
    if ($item) {
      $this->databaseQueue->createItem($item);
    }
  }

  /**
   * Remove a queue item.
   */
  public function submitRemoveItem(array &$form, FormStateInterface $form_state) {
    if ($item = $this->databaseQueue->claimItem()) {
      drupal_set_message($this->t('Removed @item', ['@item' => $item->data]));
      $this->databaseQueue->deleteItem($item);
    }
  }

  /**
   * Clear queue items, uses default form submit function.
   *
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $count = 0;
    while ($item = $this->databaseQueue->claimItem()) {
      $this->databaseQueue->deleteItem($item);
      $count++;
    }

    drupal_set_message($this->t('Cleared @count items', ['@count' => $count]));
  }
}