Message: Array to string conversion only in PHP7 Codeigniter

I have added PHP7 to my local server and I got this error:

Message: Array to string conversion Filename: libraries/Data_views_array.php Line Number: 59

data = $this->CI->$this_data[0]->$method($pass_var);

I found this post: PHP Notice: Array to string conversion only on PHP 7 and I changed my code to:

data = $this->CI->$this_data[0]->{$method($pass_var)};

but I got a different error:

Message: Call to undefined function get_page_id()

Everything works in PHP 5.6 and I don't know how to make it work in PHP 7.

Please help.

class Data_views_array {

    var $CI;

            public function __construct() {

                    $this->CI =& get_instance();

            }

            public function action_per_module($array_modules) {

               $array_to_display = array();
               $array_view_data = array();

                if (!$array_modules) {
                    return false;
                }
                else {
                    while (list($key, $this_data) = each($array_modules)) {

                        /*
                        *  $this_data[0] -  is the controller name
                        * loading this model
                        */

                       $this->CI->load->library($this_data[0]);

                          if ($this_data[2] == 'NULL') {
                               /*
                               * if there are no arguments (method and passing variable)
                               * the model is called
                               */
                               $data = $this->CI->$this_data[0];

                          }
                            else {
                              /*
                              * getting method and passing variable from arguments
                              */
                    //echo $this_data[2]. " - json<br>";
                              $obj = json_decode($this_data[2]);
                              $method = key(get_object_vars($obj));
                    //echo $method. " - method<br>";

                              $pass_var = $obj->$method;

                             /*
                              * getting data for view
                              */
                              $data = $this->CI->$this_data[0]->$method($pass_var);

                            }


                        /*
                        * name of the View
                        */
                        $view = $this_data[1];

                        /*
                        * adding the pair of View to the $array_view_data 
                        */
                        array_push($array_view_data, $view);
                        array_push($array_view_data, $data);
                        /*
                        * passing View Array to Display array
                        */
                        array_push($array_to_display, $array_view_data);
                        /*
                        * clear the array of the pair of View and passing variable
                        */
                        unset($array_view_data);
                        $array_view_data = array();

                    }
                }

                return $array_to_display;
            }

}

The first Class that is called - $this_data[0]== page_title_display from library has method: get_page_id($page_id). This class gets the Title of the page. Why the same script works in PHP 5.6 and it does not work in PHP 7? Why the get_page_id function is found in PHP 5.6 but not in PHP 7?

class Page_title_display {

    var $CI;

    public function __construct(){

            $this->CI =& get_instance();

   }

    public function get_page_id($page_id) {
        $this->CI->load->model('pageTitle_model');
        $title = $this->CI->pageTitle_model->getPagetitle($page_id);

        return $title;
    }
}