Drupal AJAX callback only getting called once - ajax

Question

I'm trying to make a form in Drupal, so more than one element can be added to a form. For example, a page might contain data for an event, then the event might have multiple dates. So I have a form that looks like:
/**
* Implements hook_form_alter().
*/
function addextra_form_alter(&$form, &$form_state) {
if ($form['#form_id'] == 'test_content_node_form' ) {
$form['elements_table'] = array(
'#theme' => 'table',
'#title' => 'Elements already added',
'#header' => array('Item', 'Remove'),
'#empty' => 'No elements',
'#prefix' => '<div id="elements-table">',
'#suffix' => '</div>',
);
$form['add_elements'] = array(
'#title' => 'Add another element',
'#type' => 'fieldset',
'#collapsible' => TRUE,
'#collapsed' => FALSE,
);
$form['add_elements']['add_content'] = array(
'#type' => 'textfield',
'#description' => t('Add an element to the table'),
'#title' => t('Add another item'),
'#size' => '12',
'#maxlength' => '60',
'#prefix' => '<div id="addextra_content">',
'#suffix' => '</div>',
);
$form['add_elements']['add_another_btn'] = array(
'#type' => 'button',
'#name' => 'add_another',
'#button_type' => 'submit',
'#executes_submit_callback' => FALSE,
'#value' => 'Add another',
'#ajax' => array(
'callback' => 'addextra_element_to_table',
),
);
}
}
When 'add_another_btn' gets clicked, it will run the ajax callback 'addextra_element_to_table.
That callback is:
function addextra_element_to_table(&$form, &$form_state) {
$form['elements_table']['#rows'][] = array($form_state['values']['add_content'], l('Remove Item', '#'));
drupal_add_js(drupal_get_path('module', 'addextra') . '/addextra.js');
return array(
'#type' => 'ajax',
'#commands' => array(
ajax_command_replace('#elements-table', render($form['elements_table'])),
),
);
}
The js file called replaces the val of the input field to ''
(function ($) {
$('#edit-add-content').val('');
})(jQuery);
But this callback only gets called one time. I believe this is because the behaviour has to be attached again once it's been called. Sorry for my ignorance - I'm not sure how to achieve this. Can anyone help me out? It would be much appreciated. Thanks in advance.

Answer 1

The problem is that render(), which basically just calls drupal_render() , does not process the #ajax element, it's simply ignored. You might want to try and pass the element through ajax_pre_render_element() before the call to render().
That said, I personally don't have good experience with trying to reuse Drupal functions outside their normal calling sequence, especially not with forms. I prefer to stick to the very top level functions, such as drupal_get_form. I have followed those functions many times in my debugger, and they do a bunch of things in a precise order that is hard to get a hold of when you want to reuse pieces of that.
To alter a form with AJAX callbacks, I would always prefer one of two strategies:
In the callback, adjust the content of the $form argument and do return $form. This requires that you set #ajax['wrapper'] to the id (the value of the id attribute in the markup, as used for CSS) of the form on the originating element (the button in your case). Then Drupal gets to do its shpiel with the whole form, and the browser replaces the whole thing. Drupal takes care of preserving values already entered etc.
Alternatively, you can have the callback return a set of commands that do very specific modifications on the DOM. In your case that would be commands which create and append new rows. Keep in mind that with ajax_command_invoke(), you have the entire jQuery arsenal at your disposal.
From those two strategies, I usually prefer the second one, because it seems more elegant for little tweaks. However, if you want to build on Drupal's rendering, or if you have more massive changes to the form, you should use the first one.
As a side note, did you know that there is drupal.stackexchange.com? Drupal can be quite peculiar, and on that site, you'll find more experts on the specifics.