ajax callback on form element checkboxes

Question

I am having some troubles with ajax on form element checkboxes, in ajax callback form_state is without values and triggering element etc .. why is that?

The form is called with drupal_get_form and this is my element

$form['select_options'] = array(
  '#type' => 'checkboxes',
  '#options' => $options, 
  '#ajax' => array(
    'callback' => 'ajax_options_callback',
    'wrapper' => 'options-form',
    'event' => 'change',
    'method' => 'replace',
  ),
);

Answer 1

When you use a callback $forms and $form_state is available for use in your callback. But you should call them as parameters in your callback definition. So:

public function ajax_option_callback(array $form, FormStateInterface $form_state) {
  // get the id of the form
  $value = $form_state->getFormObject()->getFormId();
  // create a response object and return it
}

public function ajax_option_callback() {
  // $form and $form_state not available
}

Note that &form_state->getTriggeringElement() contains nothing as the form is not submitted.

I realize now the question is for D7. Maybe my answer is usefull for someone within the D8 context.