Drupal Concepts

array(
'title' => 'A page to test ajax',
'page callback' => 'drupal_get_form',
'page arguments' => array('mymodule_page'),
'access arguments' => array('access content'),
)
);
}

/**
* A form with a dropdown whose options are dependent on a
* choice made in a previous dropdown.
*
* On changing the first dropdown, the options in the second are updated.
*/
function mymodule_page($form, &$form_state) {
// Get the list of options to populate the first dropdown.
$options_first = mymodule_first_dropdown_options();

// If we have a value for the first dropdown from $form_state['values'] we use
// this both as the default value for the first dropdown and also as a
// parameter to pass to the function that retrieves the options for the
// second dropdown.
$value_dropdown_first = isset($form_state['values']['dropdown_first']) ? $form_state['values']['dropdown_first'] : key($options_first);

$form['dropdown_first'] = array(
'#type' => 'select',
'#title' => 'First Dropdown',
'#options' => $options_first,
'#default_value' => $value_dropdown_first,

// Bind an ajax callback to the change event (which is the default for the
// select form type) of the first dropdown. It will replace the second
// dropdown when rebuilt
'#ajax' => array(
// When 'event' occurs, Drupal will perform an ajax request in the
// background. Usually the default value is sufficient (eg. change for
// select elements), but valid values include any jQuery event,
// most notably 'mousedown', 'blur', and 'submit'.
'event' => 'change',
'callback' => 'mymodule_ajax_callback',
'wrapper' => 'dropdown_second_replace',
),
);
$form['dropdown_second'] = array(
'#type' => 'select',
'#title' => 'Second Dropdown',
// The entire enclosing div created here gets replaced when dropdown_first
// is changed.
'#prefix' => '

',
'#suffix' => '

',
// when the form is rebuilt during ajax processing, the $value_dropdown_first variable
// will now have the new value and so the options will change
'#options' => mymodule_second_dropdown_options($value_dropdown_first),
'#default_value' => isset($form_state['values']['dropdown_second']) ? $form_state['values']['dropdown_second'] : '',
);
return $form;
}

/**
* Selects just the second dropdown to be returned for re-rendering
*
* Since the controlling logic for populating the form is in the form builder
* function, all we do here is select the element and return it to be updated.
*
* @return renderable array (the second dropdown)
*/
function mymodule_ajax_callback($form, $form_state) {
return $form['dropdown_second'];
}

/**
* Helper function to populate the first dropdown. This would normally be
* pulling data from the database.
*
* @return array of options
*/
function mymodule_first_dropdown_options() {
return array(
'colors' => 'Names of colors',
'cities' => 'Names of cities',
'animals' => 'Names of animals',
);
}

/**
* Helper function to populate the second dropdown. This would normally be
* pulling data from the database.
*
* @param key. This will determine which set of options is returned.
*
* @return array of options
*/
function mymodule_second_dropdown_options($key = '') {
$options = array(
'colors' => array(
'red' => 'Red',
'green' => 'Green',
'blue' => 'Blue'
),
'cities' => array(
'paris' => 'Paris, France',
'tokyo' => 'Tokyo, Japan',
'newyork' => 'New York, US'
),
'animals' => array(
'dog' => 'Dog',
'cat' => 'Cat',
'bird' => 'Bird'
),
);
if (isset($options[$key])) {
return $options[$key];
}
else {
return array();
}
}

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