Form API AJAX refreshes page

Question

I need to add some AJAX functionality to a node form. Using hook_form_alter I'm overriding form elements. In this particular case I need to add a callback on the 'language' element provided by the translation module (Core, Content Translation).

However, when selecting a different option in the 'language' listbox, the page refreshes. What could trigger this behaviour?

This is the code I'm using:

function foo_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'bar_node_form') {
    $form['#prefix'] = '<div id="bar-form-wrapper">';
    $form['#suffix'] = '</div>';

    $form['language']['#ajax'] = array(
      'callback' => 'bar_form_callback',
      'wrapper' => 'bar-form-wrapper',
    );

    if (isset($form_state['values'])) {
      drupal_set_message('ajax callback');
    }
  }
}

function bar_form_callback($form, $form_state) {
  return $form;
}

Answer 1

What exactly are you trying to do? Is the page refreshing or the entire $form? What you're asking it to do is by attaching #ajax to the select is that when it changes a value resubmit the entire $form, which would probably include any submit handlers. Typically #ajax would be directed at a form element rather than the entire form.

Answer 2

since the callback is acting as a form submit, your callback (_submit) should have the same naming convention as your form id.

"bar_node_form" is your form id so:

'callback' => 'bar_node_form_submit',

Answer 3

When you specify 'callback' => 'bar_form_callback', it's not referring to a PHP callback per se. Callback in this case refers to a hook_menu() callback, in other words, the URL that JavaScript will call when the AJAX trigger is fired.

You need to define a bar_form_callback path in your custom_module_menu() function. That menu callback then call function bar_form_callback().

D.O. FAPI reference.