php - DB Connection - Singleton. How to pass users data in it?

Trying to use database connection with singleton. __constructor has been private and returning instance from static function.

class MyDbConn 
{
    protected $_conn;
    protected $database;
    protected $user;
    protected $password;
    protected $host = "localhost";
         private static $instance;


         private function __construct()
         {
              $this->db_conn = new PDO("mysql:host=$this->host;dbname=$this->database",$this->user,$this->password);
              $this->db_conn->exec("set names utf8");
              $this->_conn = $this->db_conn;
         }

         public static function returnInstance() {
              if(self::$instance == null)
              {

                  print "Object  created!";
                  self::$instance = new self;

              }

               return self::$instance;

          }

           public function returnconnection(){

            return $this->_connection;
          }
     } 

Now I can access the connection instance from MyDbConn::returnInstance()->returnconnection();

But,
How do I pass my users detail and database name to this constructor ?? I cannot do ::returnInstance($username,$password) or returnconnection($username,$password).

Any ideas please.

Answer

You can do it using global or with a normal function call

class MyDbConn 
{
    protected $_conn;
    protected $database;
    protected $user;

    protected $password;
    protected $host = "localhost";
    private static $instance;

    private function __construct()
    {

    }

    public static function returnInstance() {

         if(self::$instance == null)
         {
             print "Object  created!";
             self::$instance = new self;
         }
          return self::$instance;
     }

     private static function initDatabase(){
         $database = self::returnInstance();

         global $config;
         $database->_conn = new PDO("mysql:host={$config['host']};dbname={$config['database']}",$config['user'],$config['password']);
         $database->_conn->exec("set names utf8");
         return $database;
     }

      public static function returnconnection(){
       try {
           $db = self::initDatabase();
           return $db->_conn;

        } catch (Exception $ex) {
           echo "Error Establishing Database Connection " . $ex->getMessage();
           return null;
        }
      }
}

and pass the data like this

// will be called from initDatabase using global keyword
$config = array('host' => 'localhost', 'database' => 'db name','user' => 'user here','password' => '');

$db = MyDbConn::returnconnection();

I don't recommend Singleton, and i suggest using Dependency Injection