无法列出Google Drive API（PHP）中的文件

Question

使用Google Drive PHP客户端https://github.com/google/google-api-php-client，以下示例可以将示例文件上传到Google云端硬盘：

include_once __DIR__ . '/../vendor/autoload.php';
include_once "templates/base.php";

echo pageHeader("File Upload - Uploading a simple file");

/*************************************************
 * Ensure you've downloaded your oauth credentials
 ************************************************/
if (!$oauth_credentials = getOAuthCredentialsFile()) {
  echo missingOAuth2CredentialsWarning();
  return;
}

/************************************************
 * The redirect URI is to the current page, e.g:
 * http://localhost:8080/simple-file-upload.php
 ************************************************/
$redirect_uri = 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'];

$client = new Google_Client();
$client->setAuthConfig($oauth_credentials);
$client->setRedirectUri($redirect_uri);
$client->addScope("https://www.googleapis.com/auth/drive");
$service = new Google_Service_Drive($client);

// add "?logout" to the URL to remove a token from the session
if (isset($_REQUEST['logout'])) {
  unset($_SESSION['upload_token']);
}

/************************************************
 * If we have a code back from the OAuth 2.0 flow,
 * we need to exchange that with the
 * Google_Client::fetchAccessTokenWithAuthCode()
 * function. We store the resultant access token
 * bundle in the session, and redirect to ourself.
 ************************************************/
if (isset($_GET['code'])) {
  $token = $client->fetchAccessTokenWithAuthCode($_GET['code']);
  $client->setAccessToken($token);

  // store in the session also
  $_SESSION['upload_token'] = $token;

  // redirect back to the example
  header('Location: ' . filter_var($redirect_uri, FILTER_SANITIZE_URL));
}

// set the access token as part of the client
if (!empty($_SESSION['upload_token'])) {
  $client->setAccessToken($_SESSION['upload_token']);
  if ($client->isAccessTokenExpired()) {
    unset($_SESSION['upload_token']);
  }
} else {
  $authUrl = $client->createAuthUrl();
}

/************************************************
 * If we're signed in then lets try to upload our
 * file. For larger files, see fileupload.php.
 ************************************************/
if ($_SERVER['REQUEST_METHOD'] == 'POST' && $client->getAccessToken()) {
  // We'll setup an empty 1MB file to upload.
  DEFINE("TESTFILE", 'testfile-small.txt');
  if (!file_exists(TESTFILE)) {
    $fh = fopen(TESTFILE, 'w');
    fseek($fh, 1024 * 1024);
    fwrite($fh, "!", 1);
    fclose($fh);
  }

  // This is uploading a file directly, with no metadata associated.
  $file = new Google_Service_Drive_DriveFile();
  $result = $service->files->create(
      $file,
      array(
        'data' => file_get_contents(TESTFILE),
        'mimeType' => 'application/octet-stream',
        'uploadType' => 'media'
      )
  );

  // Now lets try and send the metadata as well using multipart!
  $file = new Google_Service_Drive_DriveFile();
  $file->setName("Hello World!");
  $result2 = $service->files->create(
      $file,
      array(
        'data' => file_get_contents(TESTFILE),
        'mimeType' => 'application/octet-stream',
        'uploadType' => 'multipart'
      )
  );
}
?>

<div class="box">
<?php if (isset($authUrl)): ?>
  <div class="request">
    <a class='login' href='<?= $authUrl ?>'>Connect Me!</a>
  </div>
<?php elseif($_SERVER['REQUEST_METHOD'] == 'POST'): ?>
  <div class="shortened">
    <p>Your call was successful! Check your drive for the following files:</p>
    <ul>
      <li><a href="https://drive.google.com/open?id=<?= $result->id ?>" target="_blank"><?= $result->name ?></a></li>
      <li><a href="https://drive.google.com/open?id=<?= $result2->id ?>" target="_blank"><?= $result2->name ?></a></li>
    </ul>
  </div>
<?php else: ?>
  <form method="POST">
    <input type="submit" value="Click here to upload two small (1MB) test files" />
  </form>
<?php endif ?>
</div>

我想要实现的目标也是检索文件列表。为此，Google提供以下功能：

function retrieveAllFiles($service) {
  $result = array();
  $pageToken = NULL;

  do {
    try {
      $parameters = array();
      if ($pageToken) {
        $parameters['pageToken'] = $pageToken;
      }
      $files = $service->files->listFiles($parameters);

      $result = array_merge($result, $files->getItems());
      $pageToken = $files->getNextPageToken();
    } catch (Exception $e) {
      print "An error occurred: " . $e->getMessage();
      $pageToken = NULL;
    }
  } while ($pageToken);
  return $result;
}

所以..我试图在第一个例子中集成列表文件功能，这是成功连接到谷歌驱动器。但是，无论我如何组合它们，都不会返回任何内容。

有关如何使用第一个示例中的身份验证列出文件的任何提示，但非常棒。谢谢！