Getting an error adding a new field with a custom Field Type

Question

I defined a new Field Type named country following this nice tutorial: http://capgemini.github.io/drupal/writing-custom-fields-in-drupal-8/

These are main files from the country custom Field Type:

modules/custom/country/src/Plugin/Field/FieldType/CountryItem.php

/**
 * Plugin implementation of the 'country' field type.
 *
 * @FieldType(
 *   id = "country",
 *   label = @Translation("Country"),
 *   description = @Translation("Stores the ISO-2 name of a country."),
 *   category = @Translation("Custom"),
 *   default_widget = "country_default",
 *   default_formatter = "country_default"
 * )
 */
class CountryItem extends FieldItemBase {

  const COUNTRY_ISO2_MAXLENGTH = 2;

  /**
   * {@inheritdoc}
   */
  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
    $properties['value'] = DataDefinition::create('string')
      ->setLabel(t('Country'));
    return $properties;
  }

  /**
   * {@inheritdoc}
   */
  public static function schema(FieldStorageDefinitionInterface $field_definition) {
    return array(
      'columns' => array(
        'value' => array(
          'type' => 'char',
          'length' => static::COUNTRY_ISO2_MAXLENGTH,
          'not null' => FALSE,
        ),
      ),
      'indexes' => array(
        'value' => array('value'),
      ),
    );
  }

  /**
   * {@inheritdoc}
   */
  public function isEmpty() {
    $value = $this->get('value')->getValue();
    return $value === NULL || $value === '';
  }

  /**
   * {@inheritdoc}
   */
  public function getConstraints() {
    $constraint_manager = \Drupal::typedDataManager()->getValidationConstraintManager();
    $constraints = parent::getConstraints();
    $constraints[] = $constraint_manager->create('ComplexData', array(
      'value' => array(
        'Length' => array(
          'max' => static::COUNTRY_ISO2_MAXLENGTH,
          'maxMessage' => t('%name: the country iso-2 code may not be longer than @max characters.', array('%name' => $this->getFieldDefinition()->getLabel(), '@max' => static::COUNTRY_ISO2_MAXLENGTH)),
        )
      ),
    ));
    return $constraints;
  }
}

modules/custom/country/src/Plugin/Field/FieldFormatter/CountryDefaultFormatter.php

/**
 * Plugin implementation of the 'country' formatter.
 *
 * @FieldFormatter(
 *   id = "country_default",
 *   module = "country",
 *   label = @Translation("Country"),
 *   field_types = {
 *     "country"
 *   }
 * )
 */
class CountryDefaultFormatter extends FormatterBase {

  /**
   * {@inheritdoc}
   */
  public function viewElements(FieldItemListInterface $items) {
    $elements = array();
    $countries = \Drupal::service('country_manager')->getList();
    foreach ($items as $delta => $item) {
      if (isset($countries[$item->value])) {
        $elements[$delta] = array('#markup' => $countries[$item->value]);
      }
    }
    return $elements;
  }

}

modules/custom/country/src/Plugin/Field/FieldWidget/CountryDefaultWidget.php

/**
 * Plugin implementation of the 'country_default' widget.
 *
 * @FieldWidget(
 *   id = "country_default",
 *   label = @Translation("Country select"),
 *   field_types = {
 *     "country"
 *   }
 * )
 */
class CountryDefaultWidget extends WidgetBase {

  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    $countries = \Drupal::service('country_manager')->getList();
    $element['value'] = $element + array(
        '#type' => 'select',
        '#options' => $countries,
        '#empty_value' => '',
        '#default_value' => (isset($items[$delta]->value) && isset($countries[$items[$delta]->value])) ? $items[$delta]->value : NULL,
        '#description' => t('Select a country'),
      );
    return $element;
  }

}

All works fine: I'm able to create new fields of type country and set values on them.

The only problem is when I add a new field of type country in some Content Type, when I click the "Save and continue" button (after set a value for the field's label) I get a 500 http error page inside the browser and this error in the PHP log:

PHP Fatal error: Declaration of Drupal\country\Plugin\Field\FieldFormatter\CountryDefaultFormatter::viewElements() must be compatible with Drupal\Core\Field\FormatterInterface::viewElements(Drupal\Core\Field\FieldItemListInterface $items, $langcode) in /path/to/drupal/website/modules/custom/country/src/Plugin/Field/FieldFormatter/CountryDefaultFormatter.php on line 0

What is wrong?

Answer 1

Your tutorial is outdated, as the error says, viewElements() has an additional langcode argument that you need to add as well.