--- /dev/null
+<?php
+
+namespace Drupal\field_test\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FormatterBase;
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Plugin implementation of the 'field_test_with_prepare_view' formatter.
+ *
+ * @FieldFormatter(
+ * id = "field_test_with_prepare_view",
+ * label = @Translation("With prepare step"),
+ * description = @Translation("Tests prepareView() method"),
+ * field_types = {
+ * "test_field"
+ * },
+ * weight = 10
+ * )
+ */
+class TestFieldPrepareViewFormatter extends FormatterBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function defaultSettings() {
+ return [
+ 'test_formatter_setting_additional' => 'dummy test string',
+ ] + parent::defaultSettings();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function settingsForm(array $form, FormStateInterface $form_state) {
+ $element['test_formatter_setting_additional'] = [
+ '#title' => t('Setting'),
+ '#type' => 'textfield',
+ '#size' => 20,
+ '#default_value' => $this->getSetting('test_formatter_setting_additional'),
+ '#required' => TRUE,
+ ];
+ return $element;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function settingsSummary() {
+ $summary = [];
+ $summary[] = t('@setting: @value', ['@setting' => 'test_formatter_setting_additional', '@value' => $this->getSetting('test_formatter_setting_additional')]);
+ return $summary;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function prepareView(array $entities_items) {
+ foreach ($entities_items as $items) {
+ foreach ($items as $item) {
+ // Don't add anything on empty values.
+ if (!$item->isEmpty()) {
+ $item->additional_formatter_value = $item->value + 1;
+ }
+ }
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function viewElements(FieldItemListInterface $items, $langcode) {
+ $elements = [];
+
+ foreach ($items as $delta => $item) {
+ $elements[$delta] = ['#markup' => $this->getSetting('test_formatter_setting_additional') . '|' . $item->value . '|' . $item->additional_formatter_value];
+ }
+
+ return $elements;
+ }
+
+}