Custom field type with showon attribute for list options

Question

When creating a showon attribute in list options one can do that in form XML since Joomla 3.9 like this:

<field name="fieldx" type="list" default="0" label="MYFIELDX">
    <option value="0">0</option>
    <option value="1">1</option>
</field>

<field name="myfield" type="list" default="0" label="MYFIELD">
    <option value="0">A</option>
    <option value="1">B</option>
    <option value="2" showon="fieldx:1">C</option> 
    <option value="3">D</option>
</field>

I want to do that in a small custom field type I'm using in my component. Question is how can i add the showon attribute to options dynamically? I checked the pull request it was introduced by with no luck: https://github.com/joomla/joomla-cms/pull/18998

defined('JPATH_BASE') or die;

use Joomla\CMS\Factory;
use Joomla\CMS\Language\Text;
use Joomla\CMS\Form\FormHelper;

FormHelper::loadFieldClass('list');

class JFormFieldObjecttypes extends JFormFieldList
{
    protected $type = 'Objecttypes';

    public function getOptions()
    {
        $options = array();
        $db = Factory::getDbo();

        $query = $db->getQuery(true);
        $query->select('id AS value, title AS text');
        $query->from('#__mytable');
        $query->where('published = 1');
        $query->order('ordering');
        $db->setQuery($query);
        $options = $db->loadObjectList();

        foreach ($options as $option) {
            $option->text = Text::_($option->text);
            $option->showon = 'fieldx:1'; // stupid ofc
        }

        return array_merge(parent::getOptions(), $options);
    }
}

Answer 1

This is what I finally did. If someone knows a cleaner solution please let me know.

defined('JPATH_BASE') or die;

use Joomla\CMS\Factory;
use Joomla\CMS\Language\Text;
use Joomla\CMS\Form\FormHelper;

FormHelper::loadFieldClass('list');

class JFormFieldObjecttypes extends JFormFieldList
{
    protected $type = 'Objecttypes';

    public function getOptions()
    {
        $options = array();
        $db = Factory::getDbo();

        $query = $db->getQuery(true);
        $query->select('id AS value, title AS text');
        $query->from('#__mytable');
        $query->where('published = 1');
        $query->order('ordering');
        $db->setQuery($query);
        $results = $db->loadObjectList();    

        $options = array();
        foreach ($results as $result) {

            // here you can do some logic that creates an array containing fieldx dependencies
            $fieldx_logic = array(1,2); // just an example

            $option =  JHTML::_('select.option', $result->value, Text::_($result->text));
            $attr = array('field' => 'jform[fieldx]', 'values' => implode(",", $fieldx_logic), 'sign' => '=', 'op' => '');
            $option->optionattr = "data-showon='[" . json_encode($attr) . "]'";
            $options[] = $option;
        }

        return array_merge(parent::getOptions(), $options);
    }
}