Introduced FileTransformBase class for File field transforms

Closes #3413192

src/Plugin/Transform/Field/FileTransformBase.php

+<?php
+
+namespace Drupal\transform_api\Plugin\Transform\Field;
+
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Core\File\FileUrlGeneratorInterface;
+use Drupal\transform_api\FieldTransformBase;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Base class for File field transform plugins.
+ */
+abstract class FileTransformBase extends FieldTransformBase {
+
+  /**
+   * File url generator.
+   *
+   * @var \Drupal\Core\File\FileUrlGeneratorInterface
+   */
+  protected $fileUrlGenerator;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * Constructs a FieldTransformBase object.
+   *
+   * @param string $plugin_id
+   *   The plugin_id for the transform.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
+   *   The definition of the field to which the transform is associated.
+   * @param array $settings
+   *   The transform settings.
+   * @param string $label
+   *   The transform label display setting.
+   * @param string $transform_mode
+   *   The transform mode.
+   * @param array $third_party_settings
+   *   Any third party settings.
+   * @param \Drupal\Core\File\FileUrlGeneratorInterface $file_url_generator
+   *   The file url generator.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   */
+  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $transform_mode, array $third_party_settings, FileUrlGeneratorInterface $file_url_generator, EntityTypeManagerInterface $entity_type_manager) {
+    parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $transform_mode, $third_party_settings);
+
+    $this->fileUrlGenerator = $file_url_generator;
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static($plugin_id, $plugin_definition, $configuration['field_definition'], $configuration['settings'], $configuration['label'], $configuration['transform_mode'], $configuration['third_party_settings'], $container->get('file_url_generator'), $container->get('entity_type.manager'));
+  }
+
+  /**
+   * Loads file entity.
+   *
+   * @param $fid
+   *
+   * @return \Drupal\file\FileInterface|null
+   *
+   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+   * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
+   */
+  protected function loadFile($fid) {
+    /** @var \Drupal\file\FileInterface|null $file */
+    $file = $this->entityTypeManager->getStorage('file')->load($fid);
+
+    return $file;
+  }
+
+}