excuse for my English. I try to retrieve my value from a custom field in com_categories. I added this field by a plugin. My value is correctly saved but i don't why, i can't retrieve my value from the field in blog_item.php file. (Of course, i ovverided this component) I used this tutorial to make the plugin : https://zunostudios.com/blog/development/203-how-to-add-custom-fields-to-articles-in-joomla

Here's my code :


// no direct access
defined ( '_JEXEC' ) or die ( 'Restricted access' );

class plgContentZfields extends JPlugin {

         * Load the language file on instantiation.
         * Note this is only available in Joomla 3.1 and higher.
         * If you want to support 3.0 series you must override the constructor
         * @var boolean
         * @since 3.1

        protected $autoloadLanguage = true;

        function onContentPrepareForm($form, $data) {

                $app = JFactory::getApplication();
                $option = $app->input->get('option');

                switch($option) {

                    case 'com_categories':
                        if ($app->isAdmin()) {

                                JForm::addFormPath(__DIR__ . '/forms');

                                //Show specific forms based on categories
                                $form->loadFile('content', false); 

                        return true;


                return true;




    <fields name="params" >
        <fieldset name="params" >

            <field name="backgroundcolor"
                label="Color of the category"

autoblog_item.php (overrided file)

<?php // Todo Not that elegant would be nice to group the params ?>
<?php $useDefList = ($params->get('show_modify_date') || $params->get('show_publish_date') || $params->get('show_create_date')
    || $params->get('show_hits') || $params->get('show_category') || $params->get('show_parent_category') || $params->get('show_author') || $assocParam); ?>

<?php if ($useDefList && ($info == 0 || $info == 2)) : ?>
    <?php // Todo: for Joomla4 joomla.content.info_block.block can be changed to joomla.content.info_block 
$attributes = json_decode($this->item->params);
echo "background".$attributes->backgroundcolor;
    <?php echo JLayoutHelper::render('joomla.content.info_block.block', array('item' => $this->item, 'params' => $params, 'position' => 'above')); ?>
<?php endif; ?>
<?php if ($info == 0 && $params->get('show_tags', 1) && !empty($this->item->tags->itemTags)) : ?>
    <?php echo JLayoutHelper::render('joomla.content.tags', $this->item->tags->itemTags); ?>
<?php endif; ?>


My final goal is to put a background-color to each category. I want to use the value in my custom field to define the background-color. Any ideas please ?

  • Can you possibly narrow down the isolated point of failure? You have several if conditions in your snippets -- can you tell us which ones are processing as expected? What is the earliest point where your code breaks? I would like to urge you not to bounce in and out of php; it makes your code very hard to read and increases the likelihood of coding typos. Your code inside of onContentPrepareForm() can be much, much simpler. When you have a single case in your switch block, just use an if statement. When you have two if conditions that perform the same action, merge them... Nov 14, 2018 at 13:57
  • In your case, since your code is either executing in the frontend or the backend AND you are doing the same thing either way -- just remove the conditions altogether and execute the lines of code unconditionally. If you are going to return true no matter what happens in the function, just return true; once at the end of the function. Nov 14, 2018 at 13:59

1 Answer 1


The category object is $this->category, not $this->item and params are a Registry object so no need for json_decode().

echo $this->category->params->get('backgroundcolor');

UPDATE: To show category params for each article based on that article's category, you need retrieve the category for each article:

$categoryParams = JCategories::getInstance('Content')->get($this->item->catid)->getParams();
echo $categoryParams->get('backgroundcolor');
  • Thanks for the answer. But It doesn't work. I mean, i replace "$attributes = json_decode($this->item->params); echo "background".$attributes->backgroundcolor;" with your proposal but nothing changes.
    – Ronis
    Nov 14, 2018 at 15:09
  • What does var_dump($this->category->params); output?
    – Sharky
    Nov 15, 2018 at 6:40
  • To clarify, are you trying to add a different background to each article based on its category?
    – Sharky
    Nov 15, 2018 at 6:45
  • var_dump($this->category->params); output a lot of things, but not ["backgroundcolor"]...
    – Ronis
    Nov 15, 2018 at 9:05
  • In the blog view, where you see the category of the article, i want to add a block with a background-color per category. For exemple, a blue background for Category 1, a red background for Category 2, etc...
    – Ronis
    Nov 15, 2018 at 9:09

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