class TableDragExampleSimpleForm

class TableDragExampleSimpleForm extends FormBase {

  /**
   * The database connection.
   *
   * @var \Drupal\Core\Database\Connection
   */
  protected $database;

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container
      ->get('database'));
  }

  /**
   * Construct a form.
   *
   * @param \Drupal\Core\Database\Connection $database
   *   The database connection.
   */
  public function __construct(Connection $database) {
    $this->database = $database;
  }

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

  /**
   * Builds the simple tabledrag form.
   *
   * @param array $form
   *   Render array representing from.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   Current form state.
   *
   * @return array
   *   The render array defining the elements of the form.
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['table-row'] = [
      '#type' => 'table',
      '#header' => [
        $this
          ->t('Name'),
        $this
          ->t('Description'),
        $this
          ->t('Weight'),
      ],
      '#empty' => $this
        ->t('Sorry, There are no items!'),
      // TableDrag: Each array value is a list of callback arguments for
      // drupal_add_tabledrag(). The #id of the table is automatically
      // prepended; if there is none, an HTML ID is auto-generated.
      '#tabledrag' => [
        [
          'action' => 'order',
          'relationship' => 'sibling',
          'group' => 'table-sort-weight',
        ],
      ],
    ];

    // Build the table rows and columns.
    //
    // The first nested level in the render array forms the table row, on which
    // you likely want to set #attributes and #weight.
    // Each child element on the second level represents a table column cell in
    // the respective table row, which are render elements on their own. For
    // single output elements, use the table cell itself for the render element.
    // If a cell should contain multiple elements, simply use nested sub-keys to
    // build the render element structure for the renderer service as you would
    // everywhere else.
    //
    // About the condition id<8:
    // For the purpose of this 'simple table' we are only using the first 8 rows
    // of the database.  The others are for 'nested' example.
    $results = $this->database
      ->select('tabledrag_example', 't')
      ->fields('t')
      ->orderBy('weight')
      ->condition('id', 8, '<')
      ->execute()
      ->fetchAll();
    foreach ($results as $row) {

      // TableDrag: Mark the table row as draggable.
      $form['table-row'][$row->id]['#attributes']['class'][] = 'draggable';

      // TableDrag: Sort the table row according to its existing/configured
      // weight.
      $form['table-row'][$row->id]['#weight'] = $row->weight;

      // Some table columns containing raw markup.
      $form['table-row'][$row->id]['name'] = [
        '#markup' => $row->name,
      ];
      $form['table-row'][$row->id]['description'] = [
        '#type' => 'textfield',
        '#required' => TRUE,
        '#default_value' => $row->description,
      ];

      // TableDrag: Weight column element.
      $form['table-row'][$row->id]['weight'] = [
        '#type' => 'weight',
        '#title' => $this
          ->t('Weight for @title', [
          '@title' => $row->name,
        ]),
        '#title_display' => 'invisible',
        '#default_value' => $row->weight,
        // Classify the weight element for #tabledrag.
        '#attributes' => [
          'class' => [
            'table-sort-weight',
          ],
        ],
      ];
    }
    $form['actions'] = [
      '#type' => 'actions',
    ];
    $form['actions']['submit'] = [
      '#type' => 'submit',
      '#value' => $this
        ->t('Save All Changes'),
    ];
    $form['actions']['cancel'] = [
      '#type' => 'submit',
      '#value' => 'Cancel',
      '#attributes' => [
        'title' => $this
          ->t('Return to TableDrag Overview'),
      ],
      '#submit' => [
        '::cancel',
      ],
      '#limit_validation_errors' => [],
    ];
    return $form;
  }

  /**
   * Form submission handler for the 'Return to' action.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  public function cancel(array &$form, FormStateInterface $form_state) {
    $form_state
      ->setRedirect('tabledrag_example.description');
  }

  /**
   * Form submission handler for the simple form.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {

    // Because the form elements were keyed with the item ids from the database,
    // we can simply iterate through the submitted values.
    $submission = $form_state
      ->getValue('table-row');
    foreach ($submission as $id => $item) {
      $this->database
        ->update('tabledrag_example')
        ->fields([
        'weight' => $item['weight'],
        'description' => $item['description'],
      ])
        ->condition('id', $id, '=')
        ->execute();
    }
  }

}