Select.php

<?php

namespace Drupal\Core\Render\Element;

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

/**
 * Provides a form element for a drop-down menu or scrolling selection box.
 *
 * Properties:
 * - #options: An associative array of options for the select. Do not use
 *   placeholders that sanitize data in any labels, as doing so will lead to
 *   double-escaping. Each array value can be:
 *   - A single translated string representing an HTML option element, where
 *     the outer array key is the option value and the translated string array
 *     value is the option label. The option value will be visible in the HTML
 *     and can be modified by malicious users, so it should not contain
 *     sensitive information and should be treated as possibly malicious data in
 *     processing.
 *   - An array representing an HTML optgroup element. The outer array key
 *     should be a translated string, and is used as the label for the group.
 *     The inner array contains the options for the group (with the keys as
 *     option values, and translated string values as option labels). Nesting
 *     option groups is not supported.
 *   - An object with an 'option' property. In this case, the outer array key
 *     is ignored, and the contents of the 'option' property are interpreted as
 *     an array of options to be merged with any other regular options and
 *     option groups found in the outer array.
 * - #sort_options: (optional) If set to TRUE (default is FALSE), sort the
 *   options by their labels, after rendering and translation is complete.
 *   Can be set within an option group to sort that group.
 * - #sort_start: (optional) Option index to start sorting at, where 0 is the
 *   first option. Can be used within an option group. If an empty option is
 *   being added automatically (see #empty_option and #empty_value properties),
 *   this defaults to 1 to keep the empty option at the top of the list.
 *   Otherwise, it defaults to 0.
 * - #empty_option: (optional) The label to show for the first default option.
 *   By default, the label is automatically set to "- Select -" for a required
 *   field and "- None -" for an optional field.
 * - #empty_value: (optional) The value for the first default option, which is
 *   used to determine whether the user submitted a value or not.
 *   - If #required is TRUE, this defaults to '' (an empty string).
 *   - If #required is not TRUE and this value isn't set, then no extra option
 *     is added to the select control, leaving the control in a slightly
 *     illogical state, because there's no way for the user to select nothing,
 *     since all user agents automatically preselect the first available
 *     option. But people are used to this being the behavior of select
 *     controls.
 *     @todo Address the above issue in Drupal 8.
 *   - If #required is not TRUE and this value is set (most commonly to an
 *     empty string), then an extra option (see #empty_option above)
 *     representing a "non-selection" is added with this as its value.
 * - #multiple: (optional) Indicates whether one or more options can be
 *   selected. Defaults to FALSE.
 * - #default_value: Must be NULL or not set in case there is no value for the
 *   element yet, in which case a first default option is inserted by default.
 *   Whether this first option is a valid option depends on whether the field
 *   is #required or not.
 * - #required: (optional) Whether the user needs to select an option (TRUE)
 *   or not (FALSE). Defaults to FALSE.
 * - #size: The number of rows in the list that should be visible at one time.
 *
 * Usage example:
 * @code
 * $form['example_select'] = [
 *   '#type' => 'select',
 *   '#title' => $this->t('Select element'),
 *   '#options' => [
 *     '1' => $this->t('One'),
 *     '2' => [
 *       '2.1' => $this->t('Two point one'),
 *       '2.2' => $this->t('Two point two'),
 *     ],
 *     '3' => $this->t('Three'),
 *   ],
 * ];
 * @endcode
 *
 * @FormElement("select")
 */
class Select extends FormElement {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        $class = get_class($this);
        return [
            '#input' => TRUE,
            '#multiple' => FALSE,
            '#sort_options' => FALSE,
            '#sort_start' => NULL,
            '#process' => [
                [
                    $class,
                    'processSelect',
                ],
                [
                    $class,
                    'processAjaxForm',
                ],
            ],
            '#pre_render' => [
                [
                    $class,
                    'preRenderSelect',
                ],
            ],
            '#theme' => 'select',
            '#theme_wrappers' => [
                'form_element',
            ],
            '#options' => [],
        ];
    }
    
    /**
     * Processes a select list form element.
     *
     * This process callback is mandatory for select fields, since all user agents
     * automatically preselect the first available option of single (non-multiple)
     * select lists.
     *
     * @param array $element
     *   The form element to process.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param array $complete_form
     *   The complete form structure.
     *
     * @return array
     *   The processed element.
     *
     * @see _form_validate()
     */
    public static function processSelect(&$element, FormStateInterface $form_state, &$complete_form) {
        // #multiple select fields need a special #name.
        if ($element['#multiple']) {
            $element['#attributes']['multiple'] = 'multiple';
            $element['#attributes']['name'] = $element['#name'] . '[]';
        }
        else {
            // If the element is set to #required through #states, override the
            // element's #required setting.
            $required = isset($element['#states']['required']) ? TRUE : $element['#required'];
            // If the element is required and there is no #default_value, then add an
            // empty option that will fail validation, so that the user is required to
            // make a choice. Also, if there's a value for #empty_value or
            // #empty_option, then add an option that represents emptiness.
            if ($required && !isset($element['#default_value']) || isset($element['#empty_value']) || isset($element['#empty_option'])) {
                $element += [
                    '#empty_value' => '',
                    '#empty_option' => $required ? t('- Select -') : t('- None -'),
                ];
                // The empty option is prepended to #options and purposively not merged
                // to prevent another option in #options mistakenly using the same value
                // as #empty_value.
                $empty_option = [
                    $element['#empty_value'] => $element['#empty_option'],
                ];
                $element['#options'] = $empty_option + $element['#options'];
            }
        }
        // Provide the correct default value for #sort_start.
        $element['#sort_start'] = $element['#sort_start'] ?? (isset($element['#empty_value']) ? 1 : 0);
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
        if ($input !== FALSE) {
            if (isset($element['#multiple']) && $element['#multiple']) {
                // If an enabled multi-select submits NULL, it means all items are
                // unselected. A disabled multi-select always submits NULL, and the
                // default value should be used.
                if (empty($element['#disabled'])) {
                    return is_array($input) ? array_combine($input, $input) : [];
                }
                else {
                    return isset($element['#default_value']) && is_array($element['#default_value']) ? $element['#default_value'] : [];
                }
            }
            elseif (isset($element['#empty_value']) && $input === (string) $element['#empty_value']) {
                return $element['#empty_value'];
            }
            else {
                return $input;
            }
        }
    }
    
    /**
     * Prepares a select render element.
     */
    public static function preRenderSelect($element) {
        Element::setAttributes($element, [
            'id',
            'name',
            'size',
        ]);
        static::setAttributes($element, [
            'form-select',
        ]);
        return $element;
    }

}