on PHP how do I get the value from a variable in a parent class?

Question

class config {
    public $pageName;

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


class header extends config {
    function display(){
        echo parent::$this->pageName;
    }

}


$config = new config('Home Page');
$header = new header();
$header->display();

This doesn't display anything, I thought it should have displayed 'Home Page'.

Any idea how i can achieve this?

Answer 1

The $header object has no relationship to the $config object. Just because their class hierarchy is connected doesn't mean that the object instances share data.

$config1 = new config('Home Page');
$config2 = new config();

Here $config2 couldn't access the value 'Home Page' either, because it's a different object. It's not a matter of class hierarchy.

Answer 2

You want to compose your objects instead of inherit their classes (aka Inversion of Control, Dependency Injection):

interface IConfig {
  public function pageName();
}
class Config implements IConfig {
    private $pageName;
    public function pageName() { return $this->pageName; }

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


class Header {
    private $config;

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

    function display(){
        echo $this->config->pageName();
    }

}


$config = new Config('Home Page');
$header = new Header($config);
$header->display();

Answer 3

$header = new header('Home Page');
$header->display();

Answer 4

$header = new header('Home Page');
$header->display();