Symfony使用表单上传文件

I am using Symfony 3.4.8 and I try to create a form for uploading a file. I followed exact the Symfony document steps but got the error:

Controller "AppBundle\Report::uploadReport()" requires that you provide a value for the "$fileUploader" argument. Either the argument is nullable and no null value has been provided, no default value has been provided or because there is a non optional argument after this one.

Here is part of my code, the rest are the same from the document except I changed the class name. Clearly when the function get called, there is no FileUploader argument passed into the function. If I remove the argument FileUploader $fileUploader, the page can load without throwing exception but it won't get the file. I am new to Symfony, how can I solve this problem?

/**
 * @Route("/report/create-report/upload/", name="report_create")
 */
public function uploadReport(Request $request, FileUploader $fileUploader)
{
    $report = new Report();
    $form = $this->createForm(ReportType::class, $report);
    $form->add('submit', SubmitType::class);
    $form->handleRequest($request);

    if ($form->isSubmitted() && $form->isValid()) {
        // $file stores the uploaded PDF file
        /** @var Symfony\Component\HttpFoundation\File\UploadedFile $file */
        $file = $report->getReport();

        $fileName = $fileUploader->upload($file);
        $report->setBrochure($fileName);
        //$fileName = $this->generateUniqueFileName().'.'.$file->guessExtension();

        // moves the file to the directory where brochures are stored
        //$file->move(
        //    $this->getParameter('reports_directory'),
        //    $fileName
        //);

        // updates the 'brochure' property to store the PDF file name
        // instead of its contents
        //$report->setReport($fileName);

        // ... persist the $product variable or any other work
    }
    return $this->render('report/createReport.html.twig', array(
        'form' => $form->createView(),
    ));
}

I have seen the post but I cannot get that answer to work on my end as there is no such variable $container.

Last update: I gave up trying implement upload from scratch. I used the recommended bundle to make it work with minimum amount of coding.

the argument brochures_directory of your FileUploader.php service seems to be emtpy. Did you specify it in service.yml? Did you also add it in your config.yml ?

And then did you clear symfony cache after change ?