PHP面向对象编程：解决父类构造器传递值在子对象方法中为空的问题

// Form 类：继承自 Controller
class Form extends Controller
{
    public function __construct()
    {
        // 调用父类构造函数，传递视图路径
        parent::__construct(__DIR__ . "/../../../themes/" . THEME . "/pages/");
    }
}

// Controller 类：负责管理视图
class Controller
{
    protected View $view; // 注意：良好的实践是使用 View 而不是 view

    public function __construct(string $pathToViews = null)
    {
        // 在 Controller 构造函数中实例化 View，并传递 pathToViews
        $this->view = new View($pathToViews);
        // 此处 var_dump($pathToViews) 会显示正确的值
        var_dump("Controller constructor received: " . $pathToViews);
    }
}

// View 类：负责处理视图请求
class View
{
    protected ?string $pathToViews; // 声明为可空字符串

    public function __construct(string $pathToViews = null)
    {
        $this->pathToViews = $pathToViews;
        // 此处 var_dump($this->pathToViews) 也会显示正确的值
        var_dump("View constructor received: " . $this->pathToViews);
    }

    // 载入视图并发送内容
    public function show(string $viewName, array $data = []): void
    {
        // 当在 Controller 外部尝试调用 View 对象的 show 方法时，
        // $this->pathToViews 可能会意外地显示为 null
        var_dump("View show method accessing: " . $this->pathToViews);
    }
}

// 假设外部尝试这样调用 (这是导致问题的原因)
// $form = new Form(); // 这会创建 Controller 和其内部的 View 实例
// $view = new View(); // 错误：这里创建了一个全新的、未初始化的 View 实例
// $view->show('some_view'); // 此时 $this->pathToViews 为 null

// Controller 类：提供 View 实例的访问器
class Controller
{
    protected View $view;

    public function __construct(string $pathToViews = null)
    {
        $this->view = new View($pathToViews);
        var_dump("Controller constructor received: " . $pathToViews);
    }

    /**
     * 获取 Controller 内部的 View 实例
     * @return View
     */
    public function getView(): View
    {
        return $this->view;
    }
}

// View 类保持不变
class View
{
    protected ?string $pathToViews;

    public function __construct(string $pathToViews = null)
    {
        $this->pathToViews = $pathToViews;
        var_dump("View constructor received: " . $this->pathToViews);
    }

    public function show(string $viewName, array $data = []): void
    {
        var_dump("View show method accessing: " . $this->pathToViews);
    }
}

// 实例化 Controller，模拟 Form 类行为
$controller = new Controller('path/to/my/views');

// 通过 getter 方法获取 Controller 内部的 View 实例
$view = $controller->getView();

// 调用 View 实例的 show 方法，此时 pathToViews 将是正确的值
$view->show('homepage');

// Controller 类：通过依赖注入接收 View 实例
class Controller
{
    protected View $view;

    /**
     * Controller 构造函数
     * @param View $view        注入的 View 实例
     * @param string|null $pathToViews 视图路径，用于配置注入的 View 实例
     */
    public function __construct(View $view, string $pathToViews = null)
    {
        $this->view = $view;
        // 将路径设置到注入的 View 实例上
        $this->view->setPathtoViews($pathToViews);

        var_dump("Controller constructor received: " . $pathToViews);
    }

    // 也可以继续提供 getView() 方法，如果需要从 Controller 内部访问
    public function getView(): View
    {
        return $this->view;
    }
}

// View 类：提供一个 setter 方法来设置视图路径
class View
{
    protected ?string $pathToViews;

    // 构造函数可以保持不变，或者根据需要调整
    public function __construct()
    {
        // 构造函数可以不接收 pathToViews，或者接收一个默认值
        $this->pathToViews = null;
    }

    /**
     * 设置视图路径
     * @param string $pathToViews
     */
    public function setPathtoViews(string $pathToViews): void
    {
        $this->pathToViews = $pathToViews;
        var_dump("View setPathtoViews called with: " . $this->pathToViews);
    }

    public function show(string $viewName, array $data = []): void
    {
        var_dump("View show method accessing: " . $this->pathToViews);
    }
}

// 1. 外部创建 View 实例
$viewInstance = new View();

// 2. 实例化 Controller，并将 View 实例和路径注入
$controller = new Controller($viewInstance, 'path/to/my/views/with/di');

// 3. 直接使用外部创建的 View 实例，它已经被 Controller 配置过
$viewInstance->show('contact_page');