yii2打开session （推荐学习：yii教程）
use yii\web\Session; $session = Yii::$app->session; // check if a session is already open if ($session->isActive) ... // open a session $session->open(); // close a session $session->close(); // destroys all data registered to a session. $session->destroy();
设置session
$session = Yii::$app->session;
$session->set('user_id', '1234');
//OR
$session['user_id'] = '1234';
//OR
$_SESSION['user_id'] = '1234';读取session
$session = Yii::$app->session;
$user_id = $session->get('user_id');
//OR
$user_id = $session['user_id'];
//OR
$user_id = isset($_SESSION['user_id']) ? $_SESSION['user_id'] : null;销毁session
$session = Yii::$app->session;
$session->remove('user_id');
//OR
unset($session['user_id']);
//OR
unset($_SESSION['user_id']); 
