how to access class variable in static method

Question

i got error Undefined class constant 'app_id' .I am trying to access the variable declared InitialSetUp class inside getFBInstance() method and this method is called from static method check_user() .I guess self keyword in this new Facebook\\Facebook([]) refers to the Facebook class thats why the error occurs but how to access the app_id and other variable in getFBInstance()

require_once __DIR__ . '/vendorFacebook/autoload.php';
class InitialSetUp{
 public $app_id = "XXXXXXXXXX";
    public $app_secret = "XXXXXXXXXX";
    public $default_graph_version = 'v2.11';

}
public function getFBInstance() {

        return new Facebook\Facebook([
            'app_id' => self::app_id, // here i am not able to access InitialSetUp' app id 
            'app_secret' => self::app_secret,
            'default_graph_version' => self::default_graph_version,
        ]);
    }

    public static function check_user() { 
 $fb = self::getFBInstance();
}

Answer 1

Since $app_id is not static you need to instantiate the IntialSetUp class. I would also advise you to look into creating get functions .

public function getFBInstance() {

    $initialSetup = new InitialSetUp();

    return new Facebook\Facebook([
        'app_id' => $initialSetup->app_id, // here i am not able to access InitialSetUp' app id 
        'app_secret' => $initialSetup->app_secret,
        'default_graph_version' => $initialSetup->default_graph_version,
    ]);
}

The self keyword refers to elements of the class where it is used and for static properties and methods.

Answer 2

call variable within class using $this

 public function getFBInstance() {

            return new Facebook\Facebook([
              'app_id' => $this->app_id, // here i am not able to access InitialSetUp' app id 
                'app_secret' => $this->app_secret,
                'default_graph_version' => $this->default_graph_version,
     ]);
    }