我的模型从控制器加载后不工作，但从另一个模型加载时工作良好

我是一个PHP初学者和编码学习者。

有一个模型从控制器加载后不工作，但从另一个模型加载时工作得很好。

我正在为用户建立一个应用程序来获得反馈。用户可以向他的听众提出几个问题。

从编码的角度来看，我有一个扩展CI_Controller的基本控制器"MY_Controller"。然后我有2个控制器，扩展我的控制器- home(主页用户将看到)和questions(查看问题的详细信息)。

我有两个主要模型:user_model和question_model

当我从user_model中加载question_model时，一切都很顺利，程序运行良好。

但是当我从Question控制器中加载question_model时，它运行构造函数(我已经做了一个echo来检查)并完成构造函数(我也做了一个echo来检查)，但是当我调用question_model的一个方法时，我得到了错误:

Fatal error: Call to a member function initialize() on a non-object in /Users/jaimequintas/Dropbox/3 CODIGO/feedbacking/application/controllers/question.php on line 17

有人能帮我一下吗?这个问题我已经纠结了一天多了，但我还是解决不了。

My base controller:

class MY_controller extends CI_Controller{

public function index()
{
    $this->session->set_userdata('user_id', 8); //this is here just to initialize a user while in DEV
    $this->prepare_user(); //populates user with DB info
}

我的问题控制器(不能使用$this->question_model方法)

class Question extends MY_Controller {
public function index(){
    parent::index();
    $active_question = $this->uri->segment(2,0);
    $this->load->model('Question_model'); //this line runs well, as an echo statement after this gets printed
    $this->Question_model->initialize($active_question); //this is the line that triggers the "can't use method error"
    $this->Question_model->get_answers_list();

这是一个Question_model，它的方法不能从控制器中调用。

class Question_model extends CI_Model {
public $question_id;
public $question_text;
public $vote_count; 
public $activation_date;
public $status; //Draft, Active, Archived
public $question_notes; //user notes
public $question_url; //the segment that will be added to codeigniter url feedbacking.me/"semgent"
public $answers_list; //array with answer objects
public $last_vote; //date of the last vote
public $vote_count_interval; //this is not computed with initialize, must call method when needed

public function __construct()
{
    parent::__construct();
}
public function initialize($question_id)
{
    //populate question from DB with: question_id, question_text, vote_count, activation_date, status
    // if $question_id ==0 creates an empty question (should be followed by create_question)

        $this->question_id = $question_id;
        $this->get_question_by_id();
        $this->get_question_votes();
}

最后是User_model。我之所以把它放在这里，是因为当这个模型加载Question_model时，一切都工作正常。

class User_model extends CI_Model {
public $user_id;
public $user_email;
public $user_name;
public $plan_id;
public $questions_list; //array with question objects


public function __construct()
{
    parent::__construct();
    $this->load->database();
}
public function initialize($user_id)
{
    //populates user_info and question_list
    $this->user_id = $user_id;
    $this->get_user_by_id();
    $this->get_user_questions(); //this line calls the Question_model and works fine
}

$CI =& get_instance();
$CI->load->model('Question_model');
$CI->Question_model->initialize($active_question);
$CI->Question_model->get_answers_list();