/**
* 组合微信app支付 获得prepayid
* @param int $order_num
*/
private function _wxpay_request($order_num = 0)
{
//判断订单编号必须是数组并且不为0
check_order_num($order_num);
//引入微信支付类
libraries_include("wxpay/", "WxPayHelper.app.php");
//支付接口发起url
$pay_url = $this->config->item("PAY_URL");
//通知地址
$notify_url = $this->config->item("WEIXIN_NOTIFY_URL");
//微信配置
$pay_config = $this->config->item("WEIXIN_PAY_NEED");
$helper = new WxPayHelper();
//随机字符串
$nonce_str = $helper->getRandChar(32);
//获得订单数据
$order_data = $this->order_model->get_one($order_num);
$data["appid"] = $pay_config['appid'];//微信开放平台审核通过的应用APPID
$data["body"] = $pay_config['body'];//商品或支付单简要描述
$data["mch_id"] = $pay_config['mch_id'];//商户号
$data["nonce_str"] = $nonce_str;//随机字符串
$data["notify_url"] = $notify_url;//通知地址
$data["out_trade_no"] = $order_data["order_num"];//商户订单号
$data["spbill_create_ip"] = $helper->get_client_ip();//终端IP
$data["total_fee"] = $order_data['total'] * 100;//总金额
$data["trade_type"] = "APP";//交易类型
$data["sign"] = $helper->getSign($data, $pay_config['partner']);//签名
$xml = $helper->arrayToXml($data);
&