File.php

<?php

namespace Drupal\Core\Render\Element;

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Render\Element;

/**
 * Provides a form element for uploading a file.
 *
 * If you add this element to a form the enctype="multipart/form-data" attribute
 * will automatically be added to the form element.
 *
 * Properties:
 * - #multiple: A Boolean indicating whether multiple files may be uploaded.
 * - #size: The size of the file input element in characters.
 *
 * @FormElement("file")
 */
class File extends FormElement {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        $class = get_class($this);
        return [
            '#input' => TRUE,
            '#multiple' => FALSE,
            '#process' => [
                [
                    $class,
                    'processFile',
                ],
            ],
            '#size' => 60,
            '#pre_render' => [
                [
                    $class,
                    'preRenderFile',
                ],
            ],
            '#theme' => 'input__file',
            '#theme_wrappers' => [
                'form_element',
            ],
        ];
    }
    
    /**
     * Processes a file upload element, make use of #multiple if present.
     */
    public static function processFile(&$element, FormStateInterface $form_state, &$complete_form) {
        if ($element['#multiple']) {
            $element['#attributes']['multiple'] = 'multiple';
            $element['#name'] .= '[]';
        }
        return $element;
    }
    
    /**
     * Prepares a #type 'file' render element for input.html.twig.
     *
     * For assistance with handling the uploaded file correctly, see the API
     * provided by file.inc.
     *
     * @param array $element
     *   An associative array containing the properties of the element.
     *   Properties used: #title, #name, #size, #description, #required,
     *   #attributes.
     *
     * @return array
     *   The $element with prepared variables ready for input.html.twig.
     */
    public static function preRenderFile($element) {
        $element['#attributes']['type'] = 'file';
        Element::setAttributes($element, [
            'id',
            'name',
            'size',
        ]);
        static::setAttributes($element, [
            'js-form-file',
            'form-file',
        ]);
        return $element;
    }

}