php - 致命错误：非抽象方法News_model :: __ construct（）必须包含主体[CodeIgniter]

我正在尝试CodeIgniter用户指南2.2.0版中的教程。我只是遵循粘贴的代码，但是却收到此错误消息。这里到底有什么问题？

Fatal error: Non-abstract method News_model::__construct() must contain 
body in /var/www/leomel/application/models/news_model.php on line 3

源代码：

<?php
class News extends CI_Controller {
   public function __construct()
   {
     parent::__construct();
     $this->load->model('news_model');
   }

   public function index()
   {
     $data['news'] = $this->news_model->get_news();
     $data['title'] = 'News archive';

     $this->load->view('templates/header', $data);
     $this->load->view('news/index', $data);
     $this->load->view('templates/footer');
   }

   public function view($slug)
   {
     $data['news'] = $this->news_model->get_news($slug);
     if (empty($data['news_item']))
     {
        show_404();
     }

     $data['title'] = $data['news_item']['title'];

     $this->load->view('templates/header', $data);
     $this->load->view('news/view', $data);
     $this->load->view('templates/footer');
   }
}

查看更多