--- /dev/null
+<?php
+
+namespace Drupal\block_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+class TestForm extends FormBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getFormId() {
+ return 'block_test_form_test';
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function buildForm(array $form, FormStateInterface $form_state) {
+ $form['email'] = [
+ '#type' => 'email',
+ '#title' => $this->t('Your .com email address.')
+ ];
+
+ $form['show'] = [
+ '#type' => 'submit',
+ '#value' => $this->t('Submit'),
+ ];
+
+ return $form;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function validateForm(array &$form, FormStateInterface $form_state) {
+ if (strpos($form_state->getValue('email'), '.com') === FALSE) {
+ $form_state->setErrorByName('email', $this->t('This is not a .com email address.'));
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function submitForm(array &$form, FormStateInterface $form_state) {
+ drupal_set_message($this->t('Your email address is @email', ['@email' => $form['email']['#value']]));
+ }
+
+}