Drupal 7 Module Development

Chapter 10
AJAX helpers
Included in Drupal is an AJAX library that integrates Drupal, jQuery, and AJAX.
This system provides a set of properties for forms and functions, to use in Drupal
callbacks, which quickly and easily build AJAX into Drupal modules. Using the
helper functions and properties AJAX can be built into Drupal pages rather than
bolted into the pages.
Adding AJAX to forms
A common use of AJAX is dynamically updating forms, based on input, to other
parts of the form. When one element in the form is updated, other elements change
or are populated with information based on a change. For an example, we can look
at an option list form element that updates a markup element.
We start with an implementation of hook_menu() to define the form page, as
seen here:
/**
* Implements hook_menu().
*/
function hello_world_menu() {
$items = array();
$items['hello_world/simple_form_example'] = array(
'title' => 'Hello World: Simple AJAX Example',
'page callback' => 'drupal_get_form',
'page arguments' => array('hello_world_simple_form_example'),
'access callback' => TRUE,
);
}
return $items;
We follow this by creating a form callback called hello_world_simple_form_
example(). This creates the form to insert into the page.
function hello_world_simple_form_example($form, &$form_state) {
$form = array();
$form['hello_city'] = array(
'#title' => t("Choose a city"),
'#type' => 'select',
'#options' => array(
t('World') => t('World'),
t('Chicago') => t('Chicago'),
t('New York') => t('New York'),
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