如何显示Joomla K2的额外字段

我有这段代码用于从数据库中的k2_items表中获取信息，但我为extra_fields获得的只是一个JSON字符串，而不是我需要打印的人类可读的id/值。

这是我用来显示数据库信息的代码，以及试图提取extra_fields值的代码。

<?php

define( '_JEXEC', 1 );
define( 'JPATH_BASE', realpath(dirname(__FILE__).'' ));
define( 'DS', DIRECTORY_SEPARATOR );
require_once ( JPATH_BASE .DS.'includes'.DS.'defines.php' );
require_once ( JPATH_BASE .DS.'includes'.DS.'framework.php' );
$mainframe =& JFactory::getApplication('site');
$mainframe->initialise();


  $user = JFactory::getUser();

  $session =& JFactory::getSession();
  $user = JFactory::getUser();
  //echo 'Username is ' . $user->username;


  if($user->username === NULL)
  //user is not logged in
  {
        exit('You are not authorized to view this page. <a href = "' . JURI::root() . '">Please return to the homepage and login using the proper username/password.</a>' . $user->username);

  }
  else
  //user is logged in
  {
    echo "<p>Welcome $user->username</p>";
    echo '<p><a href = "http://ac.tradewindus.com/index.php?option=com_content&view=featured&Itemid=143">Go here to log out</a></p>';
  $db=JFactory::getDBO();
    $sql="SELECT * FROM #__k2_items WHERE published='1'";
    $db->setQuery($sql);
    $list=$db->loadObjectList();

    foreach($list as $item)
    {
        echo "<pre>";
        echo print_r($item, true);
        echo "</pre>";
    //convertArray to use ids as key
    $extrafields = array();
    foreach($item->extra_fields as $item)
    {
    $extrafields[$item->id] = $item->value;
    }
    echo $extrafields[1];
    echo $extrafields[2];
    echo $extrafields[3];
    echo $extrafields[4];
    echo $extrafields[5];
        //echo "<p>Title: $item->title</p>";
        //echo $item->introtext;
  }
}
?>

这是我得到的每个"foreach"循环输出的结果。

stdClass Object
(
    [id] => 83
    [title] => SPEC SHEET: PANORAMAH 38 SASH BI-RAIL
    [alias] => spec-sheet-panoramah-38-sash-birail
    [catid] => 4
    [published] => 1
    [introtext] => 
SPEC SHEET: PANORAMAH 38 SASH BI-RAIL
    [fulltext] => 
    [video] => 
    [gallery] => 
    [extra_fields] => [{"id":"1","value":""},{"id":"2","value":["1"]},{"id":"3","value":["4"]},{"id":"4","value":["1","2"]},{"id":"5","value":["7"]},{"id":"6","value":["4"]}]
    [extra_fields_search] =>  PanoramAH  Minimal Frame  Door Window  Sliding  Spec Sheets  
    [created] => 2014-01-09 00:00:00
    [created_by] => 550
    [created_by_alias] => 
    [checked_out] => 0
    [checked_out_time] => 0000-00-00 00:00:00
    [modified] => 2014-08-06 22:44:57
    [modified_by] => 550
    [publish_up] => 2014-01-09 00:00:00
    [publish_down] => 0000-00-00 00:00:00
    [trash] => 0
    [access] => 1
    [ordering] => 14
    [featured] => 0
    [featured_ordering] => 0
    [image_caption] => 
    [image_credits] => 
    [video_caption] => 
    [video_credits] => 
    [hits] => 0
    [params] => {"catItemTitle":"","catItemTitleLinked":"","catItemFeaturedNotice":"","catItemAuthor":"","catItemDateCreated":"","catItemRating":"","catItemImage":"","catItemIntroText":"","catItemExtraFields":"","catItemHits":"","catItemCategory":"","catItemTags":"","catItemAttachments":"","catItemAttachmentsCounter":"","catItemVideo":"","catItemVideoWidth":"","catItemVideoHeight":"","catItemAudioWidth":"","catItemAudioHeight":"","catItemVideoAutoPlay":"","catItemImageGallery":"","catItemDateModified":"","catItemReadMore":"","catItemCommentsAnchor":"","catItemK2Plugins":"","itemDateCreated":"","itemTitle":"","itemFeaturedNotice":"","itemAuthor":"","itemFontResizer":"","itemPrintButton":"","itemEmailButton":"","itemSocialButton":"","itemVideoAnchor":"","itemImageGalleryAnchor":"","itemCommentsAnchor":"","itemRating":"","itemImage":"","itemImgSize":"","itemImageMainCaption":"","itemImageMainCredits":"","itemIntroText":"","itemFullText":"","itemExtraFields":"","itemDateModified":"","itemHits":"","itemCategory":"","itemTags":"","itemAttachments":"","itemAttachmentsCounter":"","itemVideo":"","itemVideoWidth":"","itemVideoHeight":"","itemAudioWidth":"","itemAudioHeight":"","itemVideoAutoPlay":"","itemVideoCaption":"","itemVideoCredits":"","itemImageGallery":"","itemNavigation":"","itemComments":"","itemTwitterButton":"","itemFacebookButton":"","itemGooglePlusOneButton":"","itemAuthorBlock":"","itemAuthorImage":"","itemAuthorDescription":"","itemAuthorURL":"","itemAuthorEmail":"","itemAuthorLatest":"","itemAuthorLatestLimit":"","itemRelated":"","itemRelatedLimit":"","itemRelatedTitle":"","itemRelatedCategory":"","itemRelatedImageSize":"","itemRelatedIntrotext":"","itemRelatedFulltext":"","itemRelatedAuthor":"","itemRelatedMedia":"","itemRelatedImageGallery":"","itemK2Plugins":""}
    [metadesc] => 
    [metadata] => robots=
author=
    [metakey] => 
    [plugins] => 
    [language] => *
)

额外字段应该显示在最底部，但我想没有返回任何内容。当在db输出中打印extra_fields时，值是类似[1]的数字；但当我查看K2后端时，它们是文本答案或下拉选择；人类可读。我不是一个真正的Joomla开发人员，所以我不知道是否有某种JRegistry的东西或我应该使用的东西，但我希望能被指向正确的方向。：D