构造函数 - CodeIgniter

Question

Can anyone tell me why is the constructor in controller code using parent::__construct ? I only know it is because this is to use the method in parent class which is within CI_Controller. If so, why is the constructor in model code not using parent::__construct?

class News extends CI_Controller
{

public function __construct()
{
    parent::__construct();
    $this->load->model('news_model');
} 



class News_model extends CI_Model
{
public function __construct()
{
    $this->load->database();
}

Answer 1

• The reason this line is necessary is because your local constructor will be overriding the one in the parent controller class so we need to manually call it.
• Constructors are useful if you need to set some default values, or run a default process when your class is instantiated. Constructors can't return a value, but they can do some default work.

Read Codeigniter Constructors

And Possible Duplicate of PHP Codeigniter - parent::__construct

Example

public function  __construct()
{
    parent::__construct();
    $this->load->helper('date');
    $this->load->library('session');
    $this->load->model('My_model');
    $this->load->library('cart');

}