Question

我很难理解为什么这不起作用。我可以访问我父类的属性，但不能访问对象。

我已经读过其他线程，表明我应该从下面的Session类中调用parent::__construct()，但这只会创建一个无限循环并失败。

为什么$TestVariable在Session类中可用，但$Cookie对象不可用？

主要申请文件：

class Application
{
    //Class Objects
    public $Cookie = NULL;
    public $Session = NULL;
    public $TestVariable = "Hello World";

    //Object initialization. Singleton design.
    protected function __construct()
    {
        //Initialize cookie object.
        $this->Cookie = Cookie::getCookie();

        //Initialize session object.
        $this->Session = Session::getSession();
    }

    //Returns the singleton instance of The Curator class. Singleton design.
    public static function Initialize()
    {
        static $instance = NULL;

        if($instance === NULL)
        {
            $instance = new static();
        }

        return $instance;
    }

   //Singleton design.
   private function __clone() {}

   //Singleton design.
   private function __wakeup() {}
}

Cookie文件：

class Cookie
{
    //Object initalization. Singleton design.
    protected function __construct()
    {
        //CODE HERE
    }

    //Singleton design.
    private function __clone() {}

    //Singleton design.
    private function __wakeup() {}

    //Returns the singleton instance of the cookie class. Singleton design.
    public static function getCookie()
    {
        static $cookieInstance = NULL;

        if($cookieInstance === NULL)
        {
            $cookieInstance = new static();
        }

        return $cookieInstance;
    }

    //Removes all cookies.
    public function destroyCookies()
    {
        //CODE HERE
    }
}

会话文件：

class Session extends Application
{
    //Object initialization. Singleton design.
    protected function __construct()
    {
        //This FAILS!
        $this->Cookie->destroyCookies();

        //This WORKS!
        echo $this->TestVariable;
    }

    //Singleton design.
    private function __clone() {}

    //Singleton design.
    private function __wakeup() {}

    //Returns the singleton instance of the session class. Singleton design.
    public static function getSession()
    {
        static $sessionInstance = NULL;

        if($sessionInstance === NULL)
        {
            $sessionInstance = new static();
        }

        return $sessionInstance;
    }
}

Answer 1

您需要从子类调用父构造函数。递归是因为你有这个：

会话构造函数调用parent :: __ construct（）
应用程序构造函数调用Session :: getSession（）
在Session :: getSession（）中，我们有new Session语句
调用会话构造函数
会话构造函数调用parent :: __ construct（）
......等等

因此，要使其工作，您需要打破链并将会话初始化移出Application构造函数：

class Application
{
    //Class Objects
    public $Cookie = NULL;
    public $Session = NULL;
    public $TestVariable = "Hello World";

    //Object initialization. Singleton design.
    protected function __construct()
    {
        //Initialize cookie object.
        $this->Cookie = Cookie::getCookie();
    }

    protected function init() {
        //Initialize session object.
        $this->Session = Session::getSession();
    }

    //Returns the singleton instance of The Curator class. Singleton design.
    public static function Initialize()
    {
        static $instance = NULL;

        if($instance === NULL)
        {
            $instance = new static();
            // Call init after construction
            $instance->init();
        }

        return $instance;
    }

...

这是full code。

但实际上，设计看起来不对，可能Session根本不应继承Application。

理解为什么可以从子类访问父属性但父对象不能

1 个答案: