php - 没有从子类调用父类的构造函数

Question

父类：

<?php

class Emailer {

    protected $sender;
    private $recipients;
    private $subject;
    private $body;

    function __construct($sender)
    {
        $this->sender = $sender;
        $this->recipients = array();
    }

    public function addRecipients($recipient)
    {
        array_push($this->recipients, $recipient);
    }

    public function setSubject($subject)
    {
        $this->subject = $subject;
    }

    public function setBody($body)
    {
        $this->body = $body;
    }

    public function sendEmail()
    {
        foreach($this->recipients as $recipient)
        {
            $result = mail($recipient, $this->subject, $this->body, "From: {$this->sender}\r\n");
            if($result)
                echo "Mail successfully sent to {$recipient}" . "<br/>";
        }
    }
}

儿童班：

<?php

class ExtendedEmailer extends Emailer {

    function __construct() {}

    public function setSender($sender)
    {
        $this->sender = $sender;
    }
}

现在我这样做

include_once("classes/class.emailer.php");
include_once("classes/class.extendedemailer.php");
$xemailer = new ExtendedEmailer();
$xemailer->setSender("someone@example.com");
$xemailer->addRecipients("person1@example.com");
$xemailer->setSubject("Just a Test");
$xemailer->setBody("Hi person1, How are you?");
$xemailer->sendEmail();

但这给了我以下错误......

Warning: array_push() expects parameter 1 to be array, null given in C:\\xampp\\htdocs\\oop\\classes\\class.emailer.php on line 19

Warning: Invalid argument supplied for foreach() in C:\\xampp\\htdocs\\oop\\classes\\class.emailer.php on line 34

但当我移动行$this->recipients = array(); 在其工作的addRecipient方法范围内。 这意味着不会调用父类的构造函数。 这个概念是在创建任何对象时用空数组初始化$recipient变量。 这是正常的行为吗？

修改后的父类：

<?php

class Emailer {

    protected $sender;
    private $recipients;
    private $subject;
    private $body;

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

    public function addRecipients($recipient)
    {
        $this->recipients = array();
        array_push($this->recipients, $recipient);
    }

    public function setSubject($subject)
    {
        $this->subject = $subject;
    }

    public function setBody($body)
    {
        $this->body = $body;
    }

    public function sendEmail()
    {
        foreach($this->recipients as $recipient)
        {
            $result = mail($recipient, $this->subject, $this->body, "From: {$this->sender}\r\n");
            if($result)
                echo "Mail successfully sent to {$recipient}" . "<br/>";
        }
    }
}

这给出了以下输出：

Mail successfully sent to person1@example.com

我实际上要做的是学习如何从子类访问父类的受保护属性。 在这种情况下，哪个是$sender 。

Answer 1

你必须使用parent::__construct(); 在子构造函数中

class ExtendedEmailer extends Emailer {

       function __construct($sender)
        {
           parent::__construct($sender);
        }

        public function setSender($sender)
        {
            $this->sender = $sender;
        }
    }