如何获得访问令牌facebookapi的正确方式

只是在玩facebookapi，但无法获得基本设置。已从facebookSDK下载sdk。我似乎无法使访问令牌正常工作

$fb = new Facebook'Facebook([
  'app_id' => 'keyxx',
  'app_secret' => 'key',
  'default_graph_version' => 'v2.4',
  ]);
$helper = $fb->getRedirectLoginHelper();
  $accessToken = $helper->getAccessToken();
try {
  // Returns a `Facebook'FacebookResponse` object
  $response = $fb->get('/me?fields=id,name',$accessToken);
} catch(Facebook'Exceptions'FacebookResponseException $e) {
  echo 'Graph returned an error: ' . $e->getMessage();
  exit;
} catch(Facebook'Exceptions'FacebookSDKException $e) {
  echo 'Facebook SDK returned an error: ' . $e->getMessage();
  exit;
}
$user = $response->getGraphUser();
echo 'Name: ' . $user['name'];
?>

忘了提我的应用程序是一块画布这是另一次尝试重定向，但不起作用。我看到的只是一张空白的画布

<?php
require_once 'facebook-php-sdk-v4/src/Facebook/autoload.php';
session_start()
echo 'hello';

$fb = new Facebook'Facebook([
  'app_id' => 'x',
  'app_secret' => 'y',
  'default_graph_version' => 'v2.4',
  'default_access_token' => isset($_SESSION['facebook_access_token']) ? $_SESSION['facebook_access_token'] : 'x|y'
  ]);

try {
  $response = $fb->get('/me?fields=id,name');
  $user = $response->getGraphUser();
  echo 'Name: ' . $user['name'];
  exit; //redirect, or do whatever you want
} catch(Facebook'Exceptions'FacebookResponseException $e) {
  //echo 'Graph returned an error: ' . $e->getMessage();
} catch(Facebook'Exceptions'FacebookSDKException $e) {
  //echo 'Facebook SDK returned an error: ' . $e->getMessage();
}
$helper = $fb->getRedirectLoginHelper();
$permissions = ['email', 'user_likes'];
$loginUrl = $helper->getLoginUrl('http://www.unsquaringthewheel.com/newTemp/login-callback.php', $permissions);
echo '<a href="' . $loginUrl . '">Log in with Facebook!</a>';
?>

这是回调登录页面

<?php
require_once 'facebook-php-sdk-v4/src/Facebook/autoload.php';
session_start();
$fb = new Facebook'Facebook([
  'app_id' => 'x',
  'app_secret' => 'y',
  'default_graph_version' => 'v2.4',
  'default_access_token' => 'x|y'
]);
$helper = $fb->getRedirectLoginHelper();
try {
  $accessToken = $helper->getAccessToken();
} catch(Facebook'Exceptions'FacebookResponseException $e) {
  // When Graph returns an error
  //echo 'Graph returned an error: ' . $e->getMessage();
} catch(Facebook'Exceptions'FacebookSDKException $e) {
  // When validation fails or other local issues
  //echo 'Facebook SDK returned an error: ' . $e->getMessage();
}
if (isset($accessToken)) {
  // Logged in!
  $_SESSION['facebook_access_token'] = (string) $accessToken;
} elseif ($helper->getError()) {
  // The user denied the request
}
header('Location: index.php');