单例

单例

class Db { 
    private static $instance; 
    public $handle; 
    Private function __construct($host,$username,$password,$dbname) { 
        $this->handle=NULL; 
          $this->getcon($host,$username,$password,$dbname); 
    } 
    public static function getBb() { 
          self::$instance=new Db(); 
          return self::$instance; 
    } 
    private function getcon($host,$username,$password,$dbname) { 
          if($this->handle!=NULL){ 
               return true; 
          } 
          $this->handle=mysqli_connect($host,$username,$password,$dbname); 
    } 
}