public static function newSpreadsheet($phpSpreadsheet=NULL)
    {
        if (is_object($phpSpreadsheet)) {
            
            self::$_objSpreadsheet = &$phpSpreadsheet;
        } 
        elseif (is_string($phpSpreadsheet)) {

            self::$_objSpreadsheet = \PhpOffice\PhpSpreadsheet\IOFactory::load($phpSpreadsheet);
        }
        else {
            self::$_objSpreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();
        }
        
        return self::resetSheet();
    }