code: protected function retData(array $ret)
      {
          $url = parent::retData($ret);
  
          // 发起网络请求
          try {
              $data = $this->sendReq($url);
          } catch (PayException $e) {
              throw $e;
          }
  
          // 检查是否报错
          if ($data['code'] !== '10000') {
              throw new PayException($data['sub_msg']);
          }
  
          return $data['qr_code'];
      }
docs: 处理扫码支付的返回值
  @param array $ret
  
  @throws PayException
  @return string  可生产二维码的uri
  @author helei