abstract class Mapping

1. 8.x drupal/core/lib/Drupal/Core/Config/Schema/Mapping.php \Drupal\Core\Config\Schema\Mapping
2. 8.x drupal/core/modules/views/lib/Drupal/views/Plugin/views/style/Mapping.php \Drupal\views\Plugin\views\style\Mapping

MappingTest.php in drupal/core/modules/views/tests/views_test_data/lib/Drupal/views_test_data/Plugin/views/style/MappingTest.php

Definition of Drupal\views_test_data\Plugin\views\style\MappingTest;

picture.schema.yml in drupal/core/modules/picture/config/schema/picture.schema.yml

drupal/core/modules/picture/config/schema/picture.schema.yml

system.data_types.schema.yml in drupal/core/modules/system/config/schema/system.data_types.schema.yml

drupal/core/modules/system/config/schema/system.data_types.schema.yml

abstract class Mapping extends StylePluginBase {

  /**
   * Do not use grouping.
   *
   * @var bool
   */
  protected $usesGrouping = FALSE;

  /**
   * Use fields without a row plugin.
   *
   * @var bool
   */
  protected $usesFields = TRUE;

  /**
   * Builds the list of field mappings.
   *
   * @return array
   *   An associative array, keyed by the field name, containing the following
   *   key-value pairs:
   *   - #title: The human-readable label for this field.
   *   - #default_value: The default value for this field. If not provided, an
   *     empty string will be used.
   *   - #description: A description of this field.
   *   - #required: Whether this field is required.
   *   - #filter: (optional) A method on the plugin to filter field options.
   *   - #toggle: (optional) If this select should be toggled by a checkbox.
   */
  protected abstract function defineMapping();

  /**
   * Overrides Drupal\views\Plugin\views\style\StylePluginBase::defineOptions().
   */
  protected function defineOptions() {
    $options = parent::defineOptions();

    // Parse the mapping and add a default for each.
    foreach ($this
      ->defineMapping() as $key => $value) {
      $default = !empty($value['#multiple']) ? array() : '';
      $options['mapping']['contains'][$key] = array(
        'default' => isset($value['#default_value']) ? $value['#default_value'] : $default,
      );
      if (!empty($value['#toggle'])) {
        $options['mapping']['contains']["toggle_{$key}"] = array(
          'default' => FALSE,
          'bool' => TRUE,
        );
      }
    }
    return $options;
  }

  /**
   * Overrides Drupal\views\Plugin\views\style\StylePluginBase::buildOptionsForm().
   */
  public function buildOptionsForm(&$form, &$form_state) {
    parent::buildOptionsForm($form, $form_state);

    // Get the mapping.
    $mapping = $this
      ->defineMapping();

    // Restrict the list of defaults to the mapping, in case they have changed.
    $options = array_intersect_key($this->options['mapping'], $mapping);

    // Get the labels of the fields added to this display.
    $field_labels = $this->displayHandler
      ->getFieldLabels();

    // Provide some default values.
    $defaults = array(
      '#type' => 'select',
      '#required' => FALSE,
      '#multiple' => FALSE,
    );

    // For each mapping, add a select element to the form.
    foreach ($options as $key => $value) {

      // If the field is optional, add a 'None' value to the top of the options.
      $field_options = array();
      $required = !empty($mapping[$key]['#required']);
      if (!$required && empty($mapping[$key]['#multiple'])) {
        $field_options = array(
          '' => t('- None -'),
        );
      }
      $field_options += $field_labels;

      // Optionally filter the available fields.
      if (isset($mapping[$key]['#filter'])) {
        $this->view
          ->initHandlers();
        $this::$mapping[$key]['#filter']($field_options);
        unset($mapping[$key]['#filter']);
      }

      // These values must always be set.
      $overrides = array(
        '#options' => $field_options,
        '#default_value' => $options[$key],
      );

      // Optionally allow the select to be toggleable.
      if (!empty($mapping[$key]['#toggle'])) {
        $form['mapping']["toggle_{$key}"] = array(
          '#type' => 'checkbox',
          '#title' => t('Use a custom %field_name', array(
            '%field_name' => strtolower($mapping[$key]['#title']),
          )),
          '#default_value' => $this->options['mapping']["toggle_{$key}"],
        );
        $overrides['#states']['visible'][':input[name="style_options[mapping][' . "toggle_{$key}" . ']"]'] = array(
          'checked' => TRUE,
        );
      }
      $form['mapping'][$key] = $overrides + $mapping[$key] + $defaults;
    }
  }

  /**
   * Overrides Drupal\views\Plugin\views\style\StylePluginBase::render().
   *
   * Provides the mapping definition as an available variable.
   */
  function render() {
    return array(
      '#theme' => $this
        ->themeFunctions(),
      '#view' => $this->view,
      '#options' => $this->options,
      '#rows' => $this->view->result,
      '#mapping' => $this
        ->defineMapping(),
    );
  }

}