Question

I am trying to generate an xml file using the below class, when an array data is passed with no depth constraints the xml gets generated by the below code successfully. I am just trying to figure out as how self::createNode($value, $child); statements works does it create a new object? what is the significance of the the parent::_construct statement in the class constructor ? as the encoding is initialized already in the child class constructor.
What I have read since now about the self keyword is that it is used to call the static methods, but here the createNode method is non static. Will someone be able to help me out in understanding the context of this statement, what I can say here is the the DomDocument class doesn’t have any createNode method at all. Will anyone be able to help?
Thank you very much.

class array2xml extends DomDocument
{
    public $nodeName;
    private $xpath;
    private $root;
    private $node_name;
    public $xml_data;

    public function __construct($root='root', $node_name='node')
    {
        parent::__construct();
        $this->encoding = "UTF-8";
        $this->formatOutput = true;
        $this->node_name = $node_name;
        $this->root = $this->appendChild($this->createElement($root));
        $this->xpath = new DomXPath($this);
    } 

    public function createNode( $arr, $node = null)
    {   
        if (is_null($node))
        {
            $node = $this->root;
        }
        foreach($arr as $element => $value) 
        {
            $element = is_numeric( $element ) 
                ? $this->node_name 
                : $element;
            $element = htmlspecialchars($element,ENT_QUOTES,'UTF-8');
            $child = $this->createElement($element, (is_array($value) 
                ? null 
                : htmlspecialchars($value,ENT_QUOTES,'UTF-8')));
            $node->appendChild($child);
            if (is_array($value))
            {
                self::createNode($value, $child);
            }
        }
    }

    public function __toString()
    {
        $this->xml_data= $this->saveXML();
        return $this->saveXML();
    }
}

Answer 1

In PHP self always refers to the class where self was executed. So in your case self will refer to a method inside the class array2xml.

Usually self is used to call static methods. Since in your case the method that is called by self isn’t static, it would have been better to use $this instead.

Where parent always calls the method from the “parent” class. So the class that is extended. Again in your case when parent::some function() is called, it will search for that method in the DomDocument class. Because that is the “parent” (extended) class.

The reason that parent::__construct() is called in the constructor of the array2xml class, is because the constructor of the extended class is never called automatically when your own class also uses a __construct(). Unless your class does not have a __construct(). Only then PHP will call the __construct() of the parent class. Otherwise you’ll have to call it manually from your own constructor.