PHP 继承 : child class overriding parent variable/property for use in constructor

Question

我有一个(抽象的)父类应该在构造期间提供功能。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;
}

问题是当未被覆盖的 Child::__construct() 运行时($this->createChannel 被 调用时，未使用被覆盖的属性NULL 参数)。

这在 PHP 中可行吗？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

事实证明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 Parent 类本身，这并不是故意的。通过使 Parent 类抽象化来修复。

经验教训:构建一个干净的测试用例，并在求助之前实际运行它。

Answer 1

我不确定您的服务器上发生了什么。我不得不对 MiddlewareTest 类做出假设，修改您的类名，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,
)'

正如您所看到的，结果是按照它们在实例化类中定义的方式传入的值，正如预期的那样。

您能否提供有关您的 MiddlewareTest 类的一些详细信息，这可能会阐明您可能遇到此行为的原因？

你运行的是什么版本的 php？