public function createUnifiedOrder($out_trade_no, $subject, $total_fee, $open_id = null)
 {
     //②、统一下单
     $input = new \WxPayUnifiedOrder();
     $input->setWxPayApi($this->wxPayApi);
     $input->SetBody($subject);
     $input->SetOut_trade_no($out_trade_no);
     //        $input->SetTotal_fee($total_fee);
     $input->SetTotal_fee(intval($total_fee * 100));
     $input->SetTime_start(date("YmdHis"));
     $input->SetTime_expire(date("YmdHis", time() + 600));
     $input->SetTrade_type($this->trade_type);
     if ($open_id) {
         $input->SetOpenid($open_id);
     }
     $order = $this->wxPayApi->unifiedOrder($input);
     return $order;
 }