I need a simple Example of a Custom Field in a Joomla 4 Component

Question

For my Project i need to have a Custom Field that gets all "Sponsors" from a related table, the user can then select the items and link them to a "location" so define the sponsors for a location. Nothing fancy In J3 I've done such things a lot but i have no clue (nor guides) on how to render the customfield correctly in J4.

form xmls got stored in /administrator/components/com_comp/forms

<!-- Repeatable Subform -->
<form>
    <field name="sponsor" type="sponsorselection" label="Sponsor" />
</form>

Fields got stored in /administrator/components/com_comp/src/Field

namespace NXD\Component\FootballManager\Form;

use Joomla\CMS\Factory;
use Joomla\CMS\Form\Field\ListField as ListField;
use Joomla\CMS\HTML\HTMLHelper;
use Joomla\CMS\Language\Text;
use Joomla\Database\DatabaseInterface;

class SponsorselectionField extends ListField
{
    protected $type = 'sponsorselection';

    protected function getOptions()
    {
        $db = Factory::getContainer()->get(DatabaseInterface::class);
        $query = $db->getQuery(true)
            ->select($db->quoteName(['id', 'title']))
            ->from($db->quoteName('#__footballmanager_sponsors'))
            ->order($db->quoteName('title'));

        $db->setQuery($query);
        $results = $db->loadObjectList();

        $options = array();
        foreach ($results as $result)
        {
            $options[] = HTMLHelper::_('select.option', $result->id, $result->name);
        }

        return $options;
    }
}

When loading this field i receive an error 500 including the info that this name (SponsorselectionField) is already in use. So the Repeatable Subform might be the issue > OK but how to handle that in the Field Class? As far as i can see there are no good example for J4 - yeah i could go the JForm J3 Way but i dont want to if there is a newer / better way...

Answer 1

OK Nevermind, 've started again from scratch and this time it worked:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Repeatable Subform -->
<form>
    <field
        name="sponsor"
        type="sponsors"
        label="COM_FOOTBALLMANAGER_SPONSOR_TITLE"
        />
</form>

Class located in administrator/com_comp/src/Field/SponsorsField.php:

namespace NXD\Component\Footballmanager\Administrator\Field;

use Joomla\CMS\Factory;
use Joomla\CMS\Form\Field\ListField;
use Joomla\CMS\HTML\HTMLHelper;
use Joomla\Database\DatabaseInterface;

defined('_JEXEC') or die;

class SponsorsField extends ListField{
    /**
     * The form field type.
     *
     * @var    string
     * @since  1.0.0
     */
    protected $type = 'Sponsors';

    /**
     * Method to get the field input markup.
     *
     * @return  string  The field input markup.
     *
     * @since   1.0.0
     */
    protected function getInput()
    {
        return parent::getInput();
    }

    /**
     * Method to get the field options.
     *
     * @return  array  The field option objects.
     *
     * @since   1.0.0
     */
    protected function getOptions()
    {
        $db = Factory::getContainer()->get(DatabaseInterface::class);
        $query = $db->getQuery(true);
        $query->select('id, title');
        $query->from('#__footballmanager_sponsors');
        $query->order('title ASC');
        $db->setQuery($query);
        $sponsors = $db->loadObjectList();

        foreach ($sponsors as $sponsor)
        {
            $options[] = HTMLHelper::_('select.option', $sponsor->id, $sponsor->title);
        }

        // Merge any additional options in the XML definition.
        $options = array_merge(parent::getOptions(), $options);

        return $options;
    }
}