function Simplest::buildForm

File

modules/ajax_example/src/Form/Simplest.php, line 23

Class

Simplest

A relatively simple AJAX demonstration form.

Namespace

Code

public function buildForm(array $form, FormStateInterface $form_state) {
  $form['change_this'] = [
    '#title' => $this->t("Choose something and explain why"),
    '#type' => 'select',
    '#options' => [
      'one' => 'one',
      'two' => 'two',
      'three' => 'three',
    ],
    '#ajax' => [
      // #ajax has two required keys: callback and wrapper.
      // callback is a callable that will be called when this element changes.
'callback' => '::promptCallback',
      // The wrapper is the HTML ID of the page element that will be replaced.
'wrapper' => 'replace-textfield-container',
    ],
  ];
  // The replace-textfield-container container will be replaced whenever
  // change_this is updated.
  $form['replace_textfield_container'] = [
    '#type' => 'container',
    '#attributes' => [
      'id' => 'replace-textfield-container',
    ],
  ];
  $form['replace_textfield_container']['replace_textfield'] = [
    '#type' => 'textfield',
    '#title' => $this->t("Why"),
  ];
  // An AJAX request calls the form builder function for every change.
  // We can change how we build the form based on $form_state.
  $value = $form_state->getValue('change_this');
  // The getValue() method returns NULL by default if the form element does
  // not exist. It won't exist yet if we're building it for the first time.
  if ($value !== NULL) {
    $form['replace_textfield_container']['replace_textfield']['#description'] = $this->t("Say why you chose '@value'", [
      '@value' => $value,
    ]);
  }
  return $form;
}