数据库连接 - 单例。 如何在其中传递用户数据？

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.

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

<?php
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

It's pretty basic question. You have your variables declared as protected which means that you can get them only inside the class. This is actually very good. To change these variables you need create get and set methods for example to change $user write methods:

public function setUser($user)
{
   $this->user = $user
}

public function getUser()
{
   return $this->user;
}

//Then you need get your object via

$db = MyDbConn::returnInstance();

//set user

$db->setUser('john');

and that's all. Moreover, singleton is call antipattern because it's hard to test and it's very similar to global variables which is not good.