session 存值的问需要解决。

用thinkphp框架
url：访问地址为 http://teac.delijy.com/index.php/index/index/zid/21Action的代码如下
public function index()
{
if(isset($_SESSION)){
session_start();
}else {
echo "首頁未開啟";
}
if($_GET['zid'])
{
  if(isset($_SESSION['zid'])){
      unset($_SESSION['zid']);
    }
echo '**********<BR>'.$_GET['zid'].'****<BR>';
$_SESSION['zid'] = $_GET['zid'];
$_SESSION['zzz'] = 6666;
}
$_SESSION['sss']=444;
echo $_SESSION['zid'];
//echo $_COOKIE['sid'];
//print_r($_SESSION);
echo "首頁<br>---------------<br>";
//print_r($_COOKIE);
$this->display();
}
public function teaching_two()
{
if(isset($_SESSION)){
session_start();
}else{
echo "內頁未開啟";
}
    echo $_SESSION['zid'];
//echo $_COOKIE['sid'];
//print_r($_SESSION);
echo "內頁<br>---------_____________------<br>";
echo $_SESSION['zzz'];
$this->display();
}在一级页面调到二级页面的时候拿不到SESSION存的值。二级页面的SESSION值竟然为css 有些不明白请指点