+<?php
+
+namespace Drupal\form_test\Form;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * A multistep form for testing the form storage.
+ *
+ * It uses two steps for editing a virtual "thing". Any changes to it are saved
+ * in the form storage and have to be present during any step. By setting the
+ * request parameter "cache" the form can be tested with caching enabled, as
+ * it would be the case, if the form would contain some #ajax callbacks.
+ */
+class FormTestStorageForm extends FormBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getFormId() {
+ return 'form_test_storage_form';
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function buildForm(array $form, FormStateInterface $form_state) {
+ if ($form_state->isRebuilding()) {
+ $form_state->setUserInput([]);
+ }
+ // Initialize
+ $storage = $form_state->getStorage();
+ if (empty($storage)) {
+ $user_input = $form_state->getUserInput();
+ if (empty($user_input)) {
+ $_SESSION['constructions'] = 0;
+ }
+ // Put the initial thing into the storage
+ $storage = [
+ 'thing' => [
+ 'title' => 'none',
+ 'value' => '',
+ ],
+ ];
+ $form_state->setStorage($storage);
+ }
+ // Count how often the form is constructed.
+ $_SESSION['constructions']++;
+ drupal_set_message("Form constructions: " . $_SESSION['constructions']);
+
+ $form['title'] = [
+ '#type' => 'textfield',
+ '#title' => 'Title',
+ '#default_value' => $storage['thing']['title'],
+ '#required' => TRUE,
+ ];
+ $form['value'] = [
+ '#type' => 'textfield',
+ '#title' => 'Value',
+ '#default_value' => $storage['thing']['value'],
+ '#element_validate' => ['::elementValidateValueCached'],
+ ];
+ $form['continue_button'] = [
+ '#type' => 'button',
+ '#value' => 'Reset',
+ // Rebuilds the form without keeping the values.
+ ];
+ $form['continue_submit'] = [
+ '#type' => 'submit',
+ '#value' => 'Continue submit',
+ '#submit' => ['::continueSubmitForm'],
+ ];
+ $form['submit'] = [
+ '#type' => 'submit',
+ '#value' => 'Save',
+ ];
+
+ // @todo Remove this in https://www.drupal.org/node/2524408, because form
+ // cache immutability is no longer necessary, because we no longer cache
+ // forms during safe HTTP methods. In the meantime, because
+ // Drupal\system\Tests\Form still has test coverage for a poisoned form
+ // cache following a GET request, trick $form_state into caching the form
+ // to keep that test working until we either remove it or change it in
+ // that issue.
+ if ($this->getRequest()->get('immutable')) {
+ $form_state->addBuildInfo('immutable', TRUE);
+ if ($this->getRequest()->get('cache') && $this->getRequest()->isMethodSafe()) {
+ $form_state->setRequestMethod('FAKE');
+ $form_state->setCached();
+ }
+ }
+
+ return $form;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function validateForm(array &$form, FormStateInterface $form_state) {
+ if ($this->getRequest()->get('cache')) {
+ // Manually activate caching, so we can test that the storage keeps working
+ // when it's enabled.
+ $form_state->setCached();
+ }
+ }
+
+ /**
+ * Form element validation handler for 'value' element.
+ *
+ * Tests updating of cached form storage during validation.
+ */
+ public function elementValidateValueCached($element, FormStateInterface $form_state) {
+ // If caching is enabled and we receive a certain value, change the storage.
+ // This presumes that another submitted form value triggers a validation error
+ // elsewhere in the form. Form API should still update the cached form storage
+ // though.
+ if ($this->getRequest()->get('cache') && $form_state->getValue('value') == 'change_title') {
+ $form_state->set(['thing', 'changed'], TRUE);
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function continueSubmitForm(array &$form, FormStateInterface $form_state) {
+ $form_state->set(['thing', 'title'], $form_state->getValue('title'));
+ $form_state->set(['thing', 'value'], $form_state->getValue('value'));
+ $form_state->setRebuild();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function submitForm(array &$form, FormStateInterface $form_state) {
+ drupal_set_message("Title: " . Html::escape($form_state->getValue('title')));
+ drupal_set_message("Form constructions: " . $_SESSION['constructions']);
+ if ($form_state->has(['thing', 'changed'])) {
+ drupal_set_message("The thing has been changed.");
+ }
+ $form_state->setRedirect('<front>');
+ }
+
+}