当控制器类扩展父控制器时，为什么还需要父构造函数？ [英] why do we still need parent constructor when controller class extends a parent controller?

问题描述

我是CodeIgniter和OOP的初学者。我正在阅读CI教程页面此处。我发现了一些在我脑海中提出问题的东西。

看看这段代码：

I'm a beginner in CodeIgniter and OOP. I was reading a page of CI tutorial here. I found something that made a question in my mind.
Look at this code:

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

我认为如果我们创建了一个扩展CI_Controller的类，我们认为它必须具有其父类中的所有方法和属性（虽然我们可以覆盖它们）。那么，为什么代码中有 parent :: __ construct（）; ？

I think if we made a class that extends CI_Controller, we assume it must have all methods and properties in its parent class (Although we can override them). So, why there is parent::__construct(); in the code?

推荐答案

__ construct（）是类的构造方法。如果您从中声明一个新的对象实例，它将运行。但是，它只运行自身的构造函数，而不是它的父元素。例如：

__construct() is the constructor method of a class. It runs if you declare a new object instance from it. However, it only run the constructor of itself, not of its parent. For example:

<?php

class A {
  public function __construct() {
    echo "run A's constructor\n";
  }
}

class B extends A {
  public function __construct() {
    echo "run B's constructor\n";
  }
}

// only B's constructor is invoked
// show "run B's constructor\n" only
$obj = new B();

?>

在这种情况下，如果你需要在声明$ obj时运行A类的构造函数，那么你将会需要使用 parent :: __ construct（）：

In this case, if you need to run class A's constructor when $obj is declared, you'll need to use parent::__construct():

<?php

class A {
  public function __construct() {
    echo "run A's constructor\n";
  }
}

class B extends A {
  public function __construct() {
    parent::__construct();
    echo "run B's constructor\n";
  }
}

// both constructors of A and B are invoked
// 1. show "run A's constructor\n"
// 2. show "run B's constructor\n"
$obj = new B();

?>

在CodeIgniter的情况下，该行运行CI_Controller中的构造函数。该构造函数方法应该以某种方式帮助您的控制器编码。而你只是想让它为你做好每一件事。

In CodeIgniter's case, that line runs the constructor in CI_Controller. That constructor method should have helped your controller codes in some way. And you'd just want it to do everythings for you.

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