J4. Custom frontend server side form validation

Question

Trying to create a custom validation rule in frontend, always get the same error:

0 Joomla\CMS\Form\Field\TextField::validate() rule Espaciocheck missing.

Please, will the path to the file be wrong? What could be missing?

com_aaprueba/forms/espacio.xml

<?xml version="1.0" encoding="utf-8"?>
<form addfieldprefix="Sfi\Component\Aaprueba\Site\Field">

    <fieldset addruleprefix="Sfi\Aaprueba\Site\Rule">
    
        <field 
            name="espacio" 
            type="text" 
            label="COM_AAPRUEBA_FIELD_ESPACIO" 
            description="COM_AAPRUEBA_FIELD_ESPACIO_DESC" 
            required="true"
            validate="Espaciocheck"
            />
...

com_aaprueba/tmpl/espacio/default.php

...
<form action="<?= Route::_('index.php?option=com_aaprueba&view=espacio&id='.(int) $this->item->id); ?>" method="post" name="adminForm" id="adminForm" class="form-validate">
...
<?= $this->form->renderField('espacio'); ?>
...

com_aaprueba/src/View/Espacio/HtmlView.php

namespace Sfi\Component\Aaprueba\Site\View\Espacio;
...
use Joomla\CMS\MVC\View\HtmlView as BaseHtmlView;
use Joomla\CMS\HTML\HTMLHelper;
use Joomla\CMS\HTML\Helpers\Behavior;
use Joomla\CMS\Form\FormHelper;
...

class HtmlView extends BaseHtmlView
{
...
    public function display($tpl = null)
    {
        Behavior::formvalidator();
...

com_aaprueba/src/Rule/EspaciocheckRule.php

namespace Sfi\Component\Aaprueba\Site\Rule;

\defined('_JEXEC') or die;

use Joomla\CMS\Form\FormRule;

class EspaciocheckRule extends FormRule
{
    public function test(\SimpleXMLElement $element, $value, $group = null, Registry $input = null, Form $form = null)
    {
        // Logic after working test
        return true;
    }
}

Answer 1

Thanks! Moreover I have also forgotten use Joomla\CMS\Form\Form; and use Joomla\Registry\Registry; in EspaciocheckRule.php. Now it's working fine.