Symfony Error: Attempted to call an undefined method named […] of class - php

Question

I'm currently upgrading from Symfony 2.3 to 2.8 and are deprecating for the 3.0 update.
Under the link below, I rewrite Symfony\Component\Form\Extension\Core\ChoiceList\ChoiceList and Symfony\Component\Form\Extension\Core\ChoiceList\LazyChoiceList.
Among them, the following error occurred.
I wondered if I should add getChoices(), so I added it to ChoiceLoader.php, but I still got an error.
How should I solve it?
Also, choice_list will be abolished soon, so I plan to rewrite it.
https://github.com/symfony/symfony/blob/2.7/UPGRADE-2.7.md
Error
Attempted to call an undefined method named "getChoices" of class
"Symfony\Component\Form\ChoiceList\Factory\DefaultChoiceListFactory"
ChoiceList->ChoiceLoader.php
namespace Ahi\Sp\AdminBundle\Form\ChoiceList;
//Remove
//use Symfony\Component\Form\Extension\Core\ChoiceList\ChoiceList;
//use Symfony\Component\Form\Extension\Core\ChoiceList\LazyChoiceList;
//Add
use Symfony\Component\Form\ChoiceList\Factory\DefaultChoiceListFactory;
use Symfony\Component\Form\ChoiceList\Loader\ChoiceLoaderInterface;
class StaffChoiceLoader implements ChoiceLoaderInterface
{
private $staffService;
private $loginStaff;
private $currentStaff;
public function __construct($staffService, $loginStaff)
{
$this->staffService = $staffService;
$this->loginStaff = $loginStaff;
}
public function loadChoiceList($value = null)
{
// Get the same shop staff as the login staff
$staffs = $this->staffService->getStaffByShop($this->loginStaff->getShop());
// If the current staff is not included in the acquired staff (due to transfer etc.), add it to the end
if ($this->currentStaff && !array_search($this->currentStaff, $staffs)) {
$staffs[] = $this->currentStaff;
}
//Remove
//return new ChoiceList($staffs, $staffs);
//Add
return new DefaultChoiceListFactory($staffs, $staffs);
}
//Add
public function loadChoicesForValues(array $values, $value = null)
{
if (empty($choices)) {
return array();
}
$values = array();
foreach ($choices as $person) {
$values[] = (string) $staff->getId();
}
return $values;
}
public function loadValuesForChoices(array $choices, $value= null)
{
if (empty($values)) {
return array();
}
return $this->staffService->getStaffByShop($this->loginStaff->getShop());
}
public function getChoices()
{
}
}
ArticleType.php
//Remove
//$authorChoiceList = new StaffChoiceLoader($this->staffService, $options['login_staff']);
//Add
$factory = new DefaultChoiceListFactory();
$authorChoiceList = $factory->createListFromLoader(new StaffChoiceLoader($this->staffService, $options['login_staff']));
$builder->add("author", "entity", array(
"required" => true,
"class" => "AhiSpCommonBundle:Staff",
"choice_list" => $authorChoiceList,
"empty_value" => "Please select",
));