PHP - 父類的構造函數沒有被從子類

Question

父類調用：

<?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/>"; 
     } 
    } 
} 

子類：

<?php 

class ExtendedEmailer extends Emailer { 

    function __construct() {} 

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

現在我這樣做

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(); 

但這給我以下錯誤...

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

但是當我招行$this->recipients = array();addRecipient方法它的工作範圍內。這意味着父類的構造函數不會被調用。這個概念是在創建任何對象時用空數組初始化$recipient變量。這是否是正常行爲？

修改父類：

<?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/>"; 
     } 
    } 
} 

這給出了以下的輸出：

Mail successfully sent to person1@example.com

什麼其實我試圖做的是學習如何訪問父類的protected屬性來自小孩班。在這種情況下，這是$sender。

Answer 1

你必須使用parent::__construct();兒童構造

class ExtendedEmailer extends Emailer { 

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

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