Symfony 尝试新命令时出现错误“无法访问空属性”

我得到这个错误

无法访问空属性

当我尝试这个命令时abc：检查汽车

改变

到

---

注意管理者前面的$this->$manager->仔细观察。看到你的语法有什么问题吗？是的就像Sergei说的是$。。。谢谢

<?php

namespace CarBundle\Command;

use Symfony\Bundle\FrameworkBundle\Command\ContainerAwareCommand;
use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Helper\ProgressBar;
use Symfony\Component\Console\Input\InputArgument;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Input\InputOption;
use Symfony\Component\Console\Output\OutputInterface;

class AbcCheckCarCommand extends Command
{
    protected $carChecker;
    protected $manager;

    /**
     * AbcCheckCarCommand constructor.
     * @param $carChecker
     * @param $manager
     */
    public function __construct($carChecker, $manager)
    {
        $this->carChecker = $carChecker;
        $this->manager = $manager;

        parent::__construct();
    }

    protected function configure()
    {
        $this
            ->setName('abc:check-car')
            ->setDescription('...')
            ->addArgument('format', InputArgument::OPTIONAL, 'format progress bar')
            ->addOption('option', null, InputOption::VALUE_NONE, 'Option description')
        ;
    }

    protected function execute(InputInterface $input, OutputInterface $output)
    {
        $carRepository = $this->$manager->getRepository('CarBundle:Car');
        $cars = $carRepository->findAll();

        $bar = new ProgressBar($output, count($cars));

        $argument = $input->getArgument('format');
        $bar->setFormat($argument);

        $bar->start();

        foreach ($cars as $car)
        {
            $this->carChecker->checkCar($car);
            sleep(1);
            $bar->advance();
        }
        $bar->finish();

    }

}

$carRepository = $this->$manager->getRepository('CarBundle:Car');

$carRepository = $this->manager->getRepository('CarBundle:Car');