PHP继承：子类覆盖父变量/属性以在构造函数中使用

Question

我有一个（抽象的）父类应该在构建期间提供功能。子类可以覆盖构造函数中使用的属性：

class Parent extends MiddlewareTest
{
    // abstract channel properties
    protected $title = NULL;
    protected $type = NULL;
    protected $resolution = NULL;

    function __construct() {
        parent::__construct();

        $this->uuid = $this->createChannel($this->title, $this->type, $this->resolution);
    }
}

class Child extends Parent
{
    // channel properties
    protected $title = 'Power';
    protected $type = 'power';
    protected $resolution = 1000;
}

问题是在运行未被覆盖的Child::__construct() 时不使用被覆盖的属性（$this->createChannel 使用NULL 参数调用）。

这在 PHP 中是否可行，还是我每次都必须求助于覆盖子构造函数来提供所需的功能？

注意：我看到了Properties shared between child and parents class in php，但这是不同的，因为子属性不是在构造函数中分配的，而是根据定义分配的。

更新

原来我的测试用例有问题。由于 MiddlewareTest 基于 SimpleTest 单元测试用例，SimpleTest 实际上——我没有意识到——通过它的自动运行实例化了从未有意的 Parent 类本身。通过使父类抽象来修复。

经验教训：构建一个干净的测试用例并在寻求帮助之前实际运行它。

Answer 1

我不确定您的服务器上是如何发生的。我不得不对 MiddlewareTest 类做出假设，修改你的类名，并添加一些简单的调试行，但使用以下代码：

<?php
/**
* I'm not sure what you have in this class.
* Perhaps the problem lies here on your side.
* Is this constructor doing something to nullify those properties?
* Are those properties also defined in this class?
*/
abstract class MiddlewareTest {
    // I assume this properties are also defined here
    protected $title = NULL;
    protected $type = NULL;
    protected $resolution = NULL;
    protected $uuid = NULL;

    public function __construct()
    {}

    protected function createChannel($title, $type, $resolution)
    {
        echo "<pre>" . __LINE__ . ": "; var_export(array($this->title, $this->type, $this->resolution)); echo "</pre>";
        echo "<pre>" . __LINE__ . ": "; var_export(array($title, $type, $resolution)); echo "</pre>";
        return var_export(array($title, $type, $resolution), true);
    }
}

// 'parent' is a keyword, so let's just use A and B
class A extends MiddlewareTest
{
    // abstract channel properties
    protected $title = NULL;
    protected $type = NULL;
    protected $resolution = NULL;

    function __construct() {
        parent::__construct();

        echo "<pre>" . __LINE__ . ": "; var_export(array($this->title, $this->type, $this->resolution)); echo "</pre>";
        $this->uuid = $this->createChannel($this->title, $this->type, $this->resolution);
        echo "<pre>" . __LINE__ . ": "; var_export($this->uuid); echo "</pre>";
    }
}

class B extends A
{
    // channel properties
    protected $title = "Power";
    protected $type = "power";
    protected $resolution = 1000;
}

$B = new B();
?>

我得到了这些结果：

37: array (
  0 => 'Power',
  1 => 'power',
  2 => 1000,
)

20: array (
  0 => 'Power',
  1 => 'power',
  2 => 1000,
)

21: array (
  0 => 'Power',
  1 => 'power',
  2 => 1000,
)

39: 'array (
  0 => \'Power\',
  1 => \'power\',
  2 => 1000,
)'

如您所见，结果是传入的值与在实例化类中定义的一样，正如预期的那样。

您能否提供一些有关您的 MiddlewareTest 类的详细信息，这可能有助于您了解为什么会遇到这种行为？

你运行的是什么版本的php？