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();
        }
    }

}