在PHP中解析JSON时出错

Question

我尝试解析this json file以获取使用PHP列出的所有路线值：

我不知道为什么我的代码会起作用：

$json_source = file_get_contents('https://pastebin.com/raw/TTuV7K7J');
$data = json_decode($json_source);
foreach ($data->departures as $a) {
    foreach ($a->display_informations as $b) {
        echo $b->direction . '<br />';
    }
}

我一直有这个错误：

  

尝试获取非对象的属性

echo是导致代码崩溃的行。当我显示var_dump($b)时，我为每个JSON条目获得了以下内容：

C:\wamp64\www\index.php:10:string 'Versailles-Chantiers (Versailles)' (length=33)
C:\wamp64\www\index.php:10:string 'N' (length=1)
C:\wamp64\www\index.php:10:string 'SNCF' (length=4)
C:\wamp64\www\index.php:10:
array (size=0)
  empty
C:\wamp64\www\index.php:10:string '00A092' (length=6)
C:\wamp64\www\index.php:10:string 'Paris-Montparnasse 1-2 - Versailles-Chantiers' (length=45)
C:\wamp64\www\index.php:10:string 'Train de banlieue / RER' (length=23)
C:\wamp64\www\index.php:10:string '164273' (length=6)
C:\wamp64\www\index.php:10:string 'N' (length=1)
C:\wamp64\www\index.php:10:
array (size=0)
  empty
C:\wamp64\www\index.php:10:string '' (length=0)
C:\wamp64\www\index.php:10:string 'Transilien' (length=10)
C:\wamp64\www\index.php:10:string '' (length=0)

以下是json的样子：

{
"pagination":{},
"links":[],
"disruptions":[],
"notes":[],
"feed_publishers":[],
"departures":[
          {
          "display_informations":{
                    "direction":"Versailles-Chantiers (Versailles)",
                    "code":"N",
                    "network":"SNCF",
                    "links":[],
                    "color":"00A092",
                    "name":"Paris-Montparnasse 1-2 - Versailles-Chantiers",
                    "physical_mode":"Train de banlieue \/ RER",
                    "headsign":"164273",
                    "label":"N",
                    "equipments":[],
                    "text_color":"",
                    "commercial_mode":"Transilien",
                    "description":""
          },
          "stop_point":{},
          "route":{},
          "links":[],
         "stop_date_time":{}
         },
         {...},
         {...},
],
"context":{},
"exceptions":[]
}

我应该如何获得direction值？