src/FolderDropdownField.php
public function getLastFolderID()
    {
        $request = Controller::curr()->getRequest();
        $session = $request->getSession();
        return $session->get(self::class . '.FolderID');
    }
public function getLastFolderID()
    {
        $request = Controller::curr()->getRequest();
        $session = $request->getSession();
        return $session->get(self::class . '.FolderID');
    }
Get the last folder selected

@return int