PHP dependency injection child class

Question

let's say I have the following php classes: class user, class fileManager and class downloader extends fileManager

<?php
class user {
  private $name;
  public function __construct($name){
     $this->_name = $name;
  }
  public function getName(){
     return $this->_name;
  }
}
class fileManager {
  protected $user, $list;
  public function __construct($user, $list){
    $this->_user = $user;
    /* IF list is 1 OR 2... */
    $this->_list = $list
    /* for test: */
    echo $this->user->getName(); /* WORKS */
  }
  /* SOME METHODS */
}
class downloader extends fileManager {

  public function download($fileid){
    $this->_fileid = $fileid;
    /* if his username is set, he is logged in */
    if($this->user->getName()!=null){continue();}
  }
}

$user = new user('Jan');
echo $user->getName(); /* = jan */
$fm = new fileManager($user, 1);
$down = new downloader();
$down->download(1); 
/* FATAL ERROR, Call to a member function getName() on a non-object */
?>

So, jan is logged in, and opens the filemanager. The filemanager calls getName from the user class and knows thats it's jan. But if Jan wants to download file 1, the downloader doesn't recognize Jan. Why ? Aren't child classes supposed to inherit properties from parent classes?

You don't seem to understand inheritance: downloader extends the class filemanager, not a specific instance of the filemanager class — Mark Baker
– Mark Baker, Commented Jan 3, 2014 at 11:29

niyou · Accepted Answer · 2014-01-03 11:29:02Z

1

$down is a new object. -> The constructor needs params. Try

$user = new user('Jan');
echo $user->getName(); /* = jan */
$fm = new fileManager($user, 1);
$down = new downloader($user, 1);
$down->download(1);

answered Jan 3, 2014 at 11:29

niyou

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8 Comments

Mark Baker Over a year ago

You don't particularly even need $fm = new fileManager($user, 1);

niyou Over a year ago

i thought he may use it elsewhere

user3156884 Over a year ago

Thank you, I know it will work, but why can't the downloader class access the $user property from the fileManager class?

niyou Over a year ago

come on - lern about inheritance first

user3156884 Over a year ago

Yes, I need fileManager class, the code in the question is shrinked.

|

Stefano Esse · Accepted Answer · 2014-01-03 11:34:42Z

Not considering the typos, you have to pass values to the constructor when you instantiate the download class.

class user {
  private $name;
  public function __construct($name){
     $this->_name = $name;
  }
  public function getName(){
     return $this->_name;
  }
}
class fileManager {
  protected $user, $list;
  public function __construct($user, $list){
    $this->_user = $user;
    /* IF list is 1 OR 2... */
    $this->_list = $list;
    /* for test: */
    echo $this->_user->getName(); /* WORKS */
  }
  /* SOME METHODS */
}
class downloader extends fileManager {


  public function download($fileid){
    $this->_fileid = $fileid;
    /* if his username is set, he is logged in */
    if($this->_user->getName()==null)
        return false;

    //download file

  }
}

$user = new user('Jan');
echo $user->getName(); /* = jan */
$fm = new fileManager($user, 1);
$down = new downloader($user, 1);
$down->download(1);

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