PHP访问父类变量 [英] PHP Accessing Parent Class Variable

问题描述

  A类{
 private $ aa; 
 protected $ bb ='parent bb'; 
 
 function __construct（$ arg）{
 // do something .. 
} 
 
私有函数parentmethod（$ arg2）{
 // do something .. 
} 
} 
 
 class B extends A {
 function __construct（$ arg）{
 parent :: __ construct arg）; 
} 
 function childfunction（）{
 echo parent :: $ bb; //致命错误：未定义的类常量'bb'
} 
} 
 
 $ test = new B（$ some）; 
 $ test-> childfunction（）; 
  

问题：
如何在子级中显示父变量？
预期结果将回显'parent bb'

解决方案

  echo $ this-> bb; 
  

该变量是继承的，不是私有的，因此它是当前对象的一部分。 p>

---

这是响应您的请求的其他信息，了解有关使用 parent :: ：

当您需要添加额外功能时，使用 parent :: 到父类的方法。例如，假设一个 Airplane 类：

  class Airplane {
 private $ pilot; 
 
 public function __construct（$ pilot）{
 $ this-> pilot = $ pilot; 
} 
} 
  

现在假设我们要创建一个新类型的飞机也有一个导航器。您可以扩展__construct（）方法以添加新的功能，但仍然使用父项提供的功能：

  class Bomber extends Airplane {
 private $ navigator; 
 
 public function __construct（$ pilot，$ navigator）{
 $ this-&nav; navigator = $ navigator; 
 
 parent :: __ construct（$ pilot）; // Assigns $ pilot to $ this-> pilot 
} 
} 
  

以这种方式，您可以遵循 DRY原则的开发，但仍然提供您所需的所有功能。 / p>

class A {
    private $aa;
    protected $bb = 'parent bb';

    function __construct($arg) {
       //do something..
    }

    private function parentmethod($arg2) {
       //do something..
    }
}

class B extends A {
    function __construct($arg) {
        parent::__construct($arg);
    }
    function childfunction() {
        echo parent::$bb; //Fatal error: Undefined class constant 'bb' 
    }
}

$test = new B($some);
$test->childfunction();

Question: How do I display parent variable in child? expected result will echo 'parent bb'

解决方案

echo $this->bb;

The variable is inherited and is not private, so it is a part of the current object.

---

Here is additional information in response to your request for more information about using parent:::

Use parent:: when you want add extra functionality to a method from the parent class. For example, imagine an Airplane class:

class Airplane {
    private $pilot;

    public function __construct( $pilot ) {
        $this->pilot = $pilot;
    }
}

Now suppose we want to create a new type of Airplane that also has a navigator. You can extend the __construct() method to add the new functionality, but still make use of the functionality offered by the parent:

class Bomber extends Airplane {
    private $navigator;

    public function __construct( $pilot, $navigator ) {
        $this->navigator = $navigator;

        parent::__construct( $pilot ); // Assigns $pilot to $this->pilot
    }
}

In this way, you can follow the DRY principle of development but still provide all of the functionality you desire.

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