无法加载类型“ app_filter”：类不存在

Question

我已经将symfony 2.8项目升级到symfony 3.4。修复某些问题后，加载带有过滤器的表单页面时出现上述问题。

app_filter属性在我的bundle / resources / config目录下的form.yml文件中进行配置，如下所示，

parameters:
     app.abstract_filter.form.type.class: AppBundle\Form\Type\Filter\FilterType

services:
app.abstract_filter.form.type:
        class: '%app.abstract_filter.form.type.class%'
        arguments:
            - '@translator.default'
            - '@doctrine.orm.entity_manager'
        tags:
            - { name: form.type, alias: app_filter}

    app.abstract_filter.form:
        class: Symfony\Component\Form\Form
        factory: ['@form.factory', createNamed]
        arguments:
            - 'app_filter'
            - '%app.abstract_filter.form.type.class%'

app_abstract_fitler_form_type类：

namespace AppBundle\Form\Type\Filter;

use Doctrine\ORM\EntityManager;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Translation\Translator;

class FilterType extends AbstractType
{

    /** @var  Translator */
    protected $translator;

    /** @var  EntityManager */
    protected $entityManager;

    public function __construct(Translator $translator, EntityManager $entityManager)
    {
        $this->translator = $translator;
        $this->entityManager = $entityManager;
    }

    public function buildForm(FormBuilderInterface $builder, array $options)
    {

    }

    public function getName()
    {
        return 'app_filter';
    }
}