使用simplexml和PHP阅读Steam Web API

因此，我已经阅读了一些关于使用simpleXML读取XML的主题，但我在特定情况下遇到了问题。

目前，我正在尝试从这个来自Steam web API URL 的XML块中提取单个值

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE response>
<response>
  <players>
    <player>
        <steamid>76561197996635228</steamid>
        <communityvisibilitystate>3</communityvisibilitystate>
        <profilestate>1</profilestate>
        <personaname>P337</personaname>
        <lastlogoff>1386990920</lastlogoff>
        <commentpermission>1</commentpermission>
        <profileurl>http://steamcommunity.com/id/P337/</profileurl>
        <avatar>http://media.steampowered.com/steamcommunity/public/images/avatars/43/438f1b6217ee5600772cd1f9d978fbba999d8cc6.jpg</avatar>
        <avatarmedium>http://media.steampowered.com/steamcommunity/public/images/avatars/43/438f1b6217ee5600772cd1f9d978fbba999d8cc6_medium.jpg</avatarmedium>
        <avatarfull>http://media.steampowered.com/steamcommunity/public/images/avatars/43/438f1b6217ee5600772cd1f9d978fbba999d8cc6_full.jpg</avatarfull>
        <personastate>0</personastate>
        <primaryclanid>103582791431212131</primaryclanid>
        <timecreated>1203124452</timecreated>
        <personastateflags>0</personastateflags>
    </player>
  </players>
</response>

我可以用下面的PHP代码（代码来自另一篇文章，这对非常有用

$url = "http://api.steampowered.com/ISteamUser/GetPlayerSummaries/v0002/?key=[STEAMAPIKEY]&steamids=[PROFILEID]&format=xml";
$get = file_get_contents($url);
$xml = simplexml_load_string($get);
header('Content-Type: text/xml');
die($xml->asXML());

然而，当我试图将$xml->asXML（）更改为另一个元素时，就像文档中所说的那样：

echo '<p>'.$xml->response->players->player->personastate.'</p>;

我收到一个错误，说没有返回任何数据。

出于示例的目的，我试图检索元素<personastate>，该元素指示玩家是否在线。