FormTestValidateRequiredForm.php

<?php

namespace Drupal\form_test\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Form constructor to test the #required property.
 *
 * @internal
 */
class FormTestValidateRequiredForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_validate_required_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $options = [
            'foo' => 'foo',
            'bar' => 'bar',
        ];
        $validate = [
            '::elementValidateRequired',
        ];
        $form['textfield'] = [
            '#type' => 'textfield',
            '#title' => 'Name',
            '#required' => TRUE,
            '#required_error' => t('Enter a name.'),
        ];
        $form['checkboxes'] = [
            '#type' => 'checkboxes',
            '#title' => 'Checkboxes',
            '#options' => $options,
            '#required' => TRUE,
            '#form_test_required_error' => t('Choose at least one option.'),
            '#element_validate' => $validate,
        ];
        $form['select'] = [
            '#type' => 'select',
            '#title' => 'Select',
            '#options' => $options,
            '#required' => TRUE,
            '#form_test_required_error' => t('Select something.'),
            '#element_validate' => $validate,
        ];
        $form['radios'] = [
            '#type' => 'radios',
            '#title' => 'Radios',
            '#options' => $options,
            '#required' => TRUE,
        ];
        $form['radios_optional'] = [
            '#type' => 'radios',
            '#title' => 'Radios (optional)',
            '#options' => $options,
        ];
        $form['radios_optional_default_value_false'] = [
            '#type' => 'radios',
            '#title' => 'Radios (optional, with a default value of FALSE)',
            '#options' => $options,
            '#default_value' => FALSE,
        ];
        $form['actions'] = [
            '#type' => 'actions',
        ];
        $form['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => 'Submit',
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function elementValidateRequired($element, FormStateInterface $form_state) {
        // Set a custom validation error on the #required element.
        if (!empty($element['#required_but_empty']) && isset($element['#form_test_required_error'])) {
            $form_state->setError($element, $element['#form_test_required_error']);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->messenger()
            ->addStatus('The form_test_validate_required_form form was submitted successfully.');
    }

}