Joomla3自定义服务器端表单验证规则

我是joomla组件开发(J3, MVC)的新手，我正在尝试创建一个自定义服务器端表单验证规则。

我将validate="machinename"添加到我的表单字段，并创建了一个文件models'rules'machinename.php

defined('_JEXEC') or die('Restricted access');
jimport('joomla.form.formrule');
class JFormRuleMachinename extends JFormRule
{
    protected $regex = '/^[a-zA-Z_'x7f-'xff][a-zA-Z0-9_'x7f-'xff]*$/';
}

我有一个空的控制器在controllers'field.php

defined('_JEXEC') or die('Restricted access');
// import Joomla controllerform library
jimport('joomla.application.component.controllerform');
class SampleControllerField extends JControllerForm
{
}

，模型为models'field.php

defined('_JEXEC') or die('Restricted access');
// import Joomla modelform library
jimport('joomla.application.component.modeladmin');
/**
 * HelloWorld Model
 */
class SampleModelField extends JModelAdmin
{
    public function getTable($type = 'Field', $prefix = 'SampleTable', $config = array())
    {
        return JTable::getInstance($type, $prefix, $config);
    }
    /**
     * Method to get the record form.
     *
     * @param       array $data Data for the form.
     * @param       boolean $loadData True if the form is to load its own data (default case), false if not.
     * @return      mixed   A JForm object on success, false on failure
     * @since       2.5
     */
    public function getForm($data = array(), $loadData = true)
    {
        // Get the form.
        $form = $this->loadForm('com_sample.field', 'field',
            array('control' => 'jform', 'load_data' => $loadData));
        if (empty($form))
        {
            return false;
        }
        return $form;
    }
    /**
     * Method to get the data that should be injected in the form.
     *
     * @return      mixed   The data for the form.
     * @since       2.5
     */
    protected function loadFormData()
    {
        // Check the session for previously entered form data.
        $data = JFactory::getApplication()->getUserState('com_sample.edit.field.data', array());
        if (empty($data))
        {
            $data = $this->getItem();
        }
        return $data;
    }
}

我的组件名称是com_sample，一切都工作得很好(新建，编辑，删除)，但后来我添加了验证规则到表单的字段，现在我在提交表单时得到一个错误:

JForm::validateField() rule `machinename` missing. 

我最好的猜测是我在命名或文件位置上有一个错误，但我不确定，用谷歌找不到任何东西。