public static function getSheet($identity=null, $autoCreate=false)
    {
        // Deafult is get active sheet
        if (!$identity) {
            
            return self::$_objSheet;
        }

        // Giving $identity situation
        if (is_numeric($identity)) {
            
            $objSheet = self::$_objSpreadsheet->getSheet($identity);
            // Auto create if not exist
            if (!$objSheet && $autoCreate) {
                // Create a new sheet by index
                $objSheet = self::setSheet($identity)
                    ->getSheet();
            }
        }
        elseif (is_string($identity)) {
            
            $objSheet = self::$_objSpreadsheet->getSheetByName($identity);
            // Auto create if not exist
            if (!$objSheet && $autoCreate) {
                // Create a new sheet by name
                $objSheet = self::setSheet(null, $identity, true)
                    ->getSheet();
            }
        }

        return $objSheet;
    }