Drupal 7可折叠的字段集问题与ajax

I am sending data via ajax to my PHP callback function inside my custom module... Everything is working great. The problem I am having is: the html i am returning and rendering in the ajax complete funciton is composed of fieldsets which wont expand/collapse. Things i have tested : 1). If I render the same html ( fieldsets ) into one of the custom blocks in that same module, they work great, the collapse and expand. 2). I have tried including this inside the callback function,

  drupal_add_js('misc/form.js');
  drupal_add_js('misc/collapse.js');

inside the fieldset render array,

return array(
    '#type' => 'fieldset',
    '#title' => t($title),
'#attributes' => array(
     'class' => $class,
),
'#attached' => array(
    'js' => array(
      'misc/form.js',
      'misc/collapse.js',
    ),
  ),
);

The

$class

variable contains collapsed and collapsible. I have also tried using

#theme => 'fieldset'

Instead of #type => 'fieldset'

the javascript files

misc/collapse.js
misc/form.js

are already being included from a different function inside my module. And looking at the source of the page, are indeed being included to the head of the page.

This has to be related to bringing them in via ajax, I know when you bring elements into the document via ajax, in-order to set events for those new elements you have to use

$(document).on('event', 'class', function(){
  //code here
 });

and I am wondering if this could be the reason that the fieldsets wont collapse/expand.

If you get data with AJAX with jQuery once you have to use Drupal.behaviors like this:

Drupal.behaviors.MYBEHAVIOR = {
  attach: function (context, settings) {
    $('MYELEMENT.MYBEHAVIOR', context).once('MYBEHAVIOR', function () {
      // Apply the MYBEHAVIOR effect to the elements only once.
    });
  }
};

See more at the js documentation https://drupal.org/node/756722