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

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0

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?

2012-04-04 08:33
by matt
you could just do echo $this->pageName;Sachin 2012-04-04 08:35
+1 to counter unexplained downvote - ArjunShankar 2012-04-04 08:38

4

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.

2012-04-04 08:37
by deceze
Your explanation why this is happening is correct, but it would be nice if you could give advice how to achieve the expected (by the OP) result - knittl 2012-04-04 08:47
I can't, because what the OP is expecting doesn't make much sense. If he literally wants to achieve what his code is showing, he'd need to use static class properties, which is most likely not the right solution to his problem - deceze 2012-04-04 08:48
There are ways such as inheriting the constructor or IoC - knittl 2012-04-04 08:50
"Inheriting the constructor"? Anyway, if he wants his header instance to have access to data, the data needs to be injected into it somehow. The expectation seems to be to instantiate two different objects which can automatically share data though, which is not an expectation I can offer a reasonable solution for - deceze 2012-04-04 08:53
"Inheriting the constructor", cf @DanJ's answer (and your comement on it) – maybe that was a misnomer on my side. The OP's expectation is that it is possible to access variables from parent classes (which is possible). The thing that he is confusing, is that he creates two separate objects (as you explained in your answer). Creating a single header object with the correct constructor call will allow this. Another possibility is to use two objects together with dependency injection - knittl 2012-04-04 08:58

1

You want to compose your objects instead of inherit their classes (a.k.a. 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();
2012-04-04 08:39
by knittl

1

$header = new header('Home Page');
$header->display();
2012-04-04 08:40
by cloakedninjas
Actually, it will, unless you override it. The constructor is inherited just like the rest - deceze 2012-04-04 08:40
quite right, amende - cloakedninjas 2012-04-04 08:43

0

$header = new header('Home Page');
$header->display();
2012-04-04 08:43
by Roman Newaza
No need to declare the constructor in the header class just to call the parent's constructor. Just leave all that out, the constructor is inherited like everything else - deceze 2012-04-04 08:50
you are right! :- - Roman Newaza 2012-04-04 08:53
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