您想要检查会话变量是否设置，然后使用此。

If you want to check whether the session variable is set or not, then use this.

if($this->session->userdata('session_variable')) {

      // Do your code here
}

同时，如果你想检查会话变量是否设置了特定的值，那么你可以使用这个。

Meanwhile, if you want to check whether the session variable is set with a particular value, then you can use this.

if($this->session->userdata('session_variable') == "VALUE") {

      // Do your code here
}