class Radios

class Radios extends FormElement {
    use CompositeFormElementTrait;
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        $class = get_class($this);
        return [
            '#input' => TRUE,
            '#process' => [
                [
                    $class,
                    'processRadios',
                ],
            ],
            '#theme_wrappers' => [
                'radios',
            ],
            '#pre_render' => [
                [
                    $class,
                    'preRenderCompositeFormElement',
                ],
            ],
        ];
    }
    
    /**
     * Expands a radios element into individual radio elements.
     */
    public static function processRadios(&$element, FormStateInterface $form_state, &$complete_form) {
        if (count($element['#options']) > 0) {
            $weight = 0;
            foreach ($element['#options'] as $key => $choice) {
                // Maintain order of options as defined in #options, in case the element
                // defines custom option sub-elements, but does not define all option
                // sub-elements.
                $weight += 0.001;
                $element += [
                    $key => [],
                ];
                // Generate the parents as the autogenerator does, so we will have a
                // unique id for each radio button.
                $parents_for_id = array_merge($element['#parents'], [
                    $key,
                ]);
                $element[$key] += [
                    '#type' => 'radio',
                    '#title' => $choice,
                    // The key is sanitized in Drupal\Core\Template\Attribute during output
                    // from the theme function.
'#return_value' => $key,
                    // Use default or FALSE. A value of FALSE means that the radio button is
                    // not 'checked'.
'#default_value' => isset($element['#default_value']) ? $element['#default_value'] : FALSE,
                    '#attributes' => $element['#attributes'],
                    '#parents' => $element['#parents'],
                    '#id' => HtmlUtility::getUniqueId('edit-' . implode('-', $parents_for_id)),
                    '#ajax' => isset($element['#ajax']) ? $element['#ajax'] : NULL,
                    // Errors should only be shown on the parent radios element.
'#error_no_message' => TRUE,
                    '#weight' => $weight,
                ];
            }
        }
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
        if ($input !== FALSE) {
            // When there's user input (including NULL), return it as the value.
            // However, if NULL is submitted, FormBuilder::handleInputElement() will
            // apply the default value, and we want that validated against #options
            // unless it's empty. (An empty #default_value, such as NULL or FALSE, can
            // be used to indicate that no radio button is selected by default.)
            if (!isset($input) && !empty($element['#default_value'])) {
                $element['#needs_validation'] = TRUE;
            }
            return $input;
        }
        else {
            // For default value handling, simply return #default_value. Additionally,
            // for a NULL default value, set #has_garbage_value to prevent
            // FormBuilder::handleInputElement() converting the NULL to an empty
            // string, so that code can distinguish between nothing selected and the
            // selection of a radio button whose value is an empty string.
            $value = isset($element['#default_value']) ? $element['#default_value'] : NULL;
            if (!isset($value)) {
                $element['#has_garbage_value'] = TRUE;
            }
            return $value;
        }
    }

}