.NET微信扫码支付接入（模式二-NATIVE）

 /// <summary>
 /// 获取二维码
 /// </summary>
 /// <param name="orderNumber"></param>
 /// <returns></returns>
 public string GetCodeUrl(string orderNumber)
 {
  var result = string.Empty;
  if (!string.IsNullOrEmpty(orderNumber))
  {
  var matchedItem = db.OrderInfoForProducts.FirstOrDefault(x => x.OrderNumber == orderNumber);
  if (matchedItem != null && matchedItem.IsPaid == false)
  {
   WxPayData data = new WxPayData();
   data.SetValue("body", "productBody");//商品描述
   data.SetValue("attach", "attach data");//附加数据
   data.SetValue("out_trade_no", WxPayApi.GenerateOutTradeNo());//随机字符串
   data.SetValue("total_fee", price);//总金额
   data.SetValue("time_start", DateTime.Now.ToString("yyyyMMddHHmmss"));//交易起始时间
   data.SetValue("time_expire", DateTime.Now.AddMinutes(10).ToString("yyyyMMddHHmmss"));//交易结束时间
   data.SetValue("goods_tag", "tag");//商品标记
   data.SetValue("trade_type", "NATIVE");//交易类型
   data.SetValue("product_id", WxPayApi.GenerateOutTradeNo());//商品ID
   result = WxPayApi.UnifiedOrder(data).GetValue("code_url").ToString();//调用统一下单接口
  }
  }
  return result;
 }

 /// <summary>
 /// 根据字符串得到相应的二维码
 /// </summary>
 /// <param name="qrInfo"></param>
 /// <param name="productName"></param>
 /// <param name="version"></param>
 /// <returns></returns>
 public static Image CreateQRCodeImage(string qrInfo, string productName, string version)
 {
  try
  {
  if (!string.IsNullOrEmpty(qrInfo))
  {
   QRCodeEncoder encoder = new QRCodeEncoder
   {
   QRCodeEncodeMode = QRCodeEncoder.ENCODE_MODE.BYTE,
   QRCodeScale = 4,
   QRCodeVersion = 0,
   QRCodeErrorCorrect = QRCodeEncoder.ERROR_CORRECTION.M
   };
   //编码方式(注意：BYTE能支持中文，ALPHA_NUMERIC扫描出来的都是数字)
   //大小(值越大生成的二维码图片像素越高)
   //版本(注意：设置为0主要是防止编码的字符串太长时发生错误)
   //错误效验、错误更正(有4个等级)

   Image image = encoder.Encode(qrInfo, Encoding.GetEncoding("utf-8"));
   string filename = $"{productName}_{version}.png";
   var userLocalPath = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
   var docPath = Path.Combine(userLocalPath, @"Your Product\QRCode");
   if (!Directory.Exists(docPath))
   {
   Directory.CreateDirectory(docPath);
   }
   string filepath = Path.Combine(docPath, filename); 
   using (FileStream fs = new FileStream(filepath, FileMode.OpenOrCreate, FileAccess.Write))
   {
   image.Save(fs, System.Drawing.Imaging.ImageFormat.Png);
   fs.Close();
   image.Dispose();
   }
   return image;
  }
  }
  catch (Exception)
  {
  return null;
  }
  return null;
 }

 /// <summary>
 /// 回调函数
 /// </summary>
 public ActionResult UpdatePayStatus()
 {
  //接收从微信后台POST过来的数据
  System.IO.Stream s = Request.InputStream;
  int count = 0;
  byte[] buffer = new byte[1024];
  StringBuilder builder = new StringBuilder();
  while ((count = s.Read(buffer, 0, 1024)) > 0)
  {
  builder.Append(Encoding.UTF8.GetString(buffer, 0, count));
  }
  s.Flush();
  s.Close();
  s.Dispose();

  //转换数据格式并验证签名
  WxPayData data = new WxPayData();
  try
  {
  data.FromXml(builder.ToString());
  }
  catch (WxPayException ex)
  {
  //若签名错误，则立即返回结果给微信支付后台
  WxPayData res = new WxPayData();
  res.SetValue("return_code", "FAIL");
  res.SetValue("return_msg", ex.Message);

  LogEntity signErrorLog = new LogEntity();
  signErrorLog.errorMessage = ex.Message;
  LogHelper.WriteLog(signErrorLog, null);

  Response.Write(res.ToXml());
  Response.End();
  }

  ProcessNotify(data);  
  return View();
 }


 /// <summary>
 /// 处理回调数据
 /// </summary>
 /// <param name="data"></param>
 public void ProcessNotify(WxPayData data)
 {
  WxPayData notifyData = data;
  //检查支付结果中transaction_id是否存在
  if (!notifyData.IsSet("transaction_id"))
  {
  //若transaction_id不存在，则立即返回结果给微信支付后台
  WxPayData res = new WxPayData();
  res.SetValue("return_code", "FAIL");
  res.SetValue("return_msg", "支付结果中微信订单号不存在");

  LogEntity orderLog = new LogEntity();
  orderLog.errorMessage = "支付结果中微信订单号不存在";
  LogHelper.WriteLog(orderLog, null);

  Response.Write(res.ToXml());
  Response.End();
  }

  string transaction_id = notifyData.GetValue("transaction_id").ToString();

  //查询订单，判断订单真实性
  if (!QueryOrder(transaction_id))
  {
  //若订单查询失败，则立即返回结果给微信支付后台
  WxPayData res = new WxPayData();
  res.SetValue("return_code", "FAIL");
  res.SetValue("return_msg", "订单查询失败");

  LogEntity orderqueryLog = new LogEntity();
  orderqueryLog.errorMessage = "订单查询失败";
  LogHelper.WriteLog(orderqueryLog, null);

  Response.Write(res.ToXml());
  Response.End();
  }
  //查询订单成功
  else
  {
  WxPayData res = new WxPayData();
  res.SetValue("return_code", "SUCCESS");
  res.SetValue("return_msg", "OK");

  SetPaymentResult(data); //这里的参数是 data ！！！ 不是 res ！！！

  Response.Write(res.ToXml());
  Response.End();
  }
 }

 /// <summary>
 /// 商户后台更新
 /// </summary>
 /// <param name="res"></param>
 private void SetPaymentResult(WxPayData res)
 {
  var isSucessFlagOne = res.GetValue("return_code").ToString();
  var isSuccessFlagTwo = res.GetValue("result_code").ToString();
  
  if (isSucessFlagOne == "SUCCESS" && isSuccessFlagTwo == "SUCCESS")
  {
  //自己的业务逻辑 ！！！！
  }
 }

 //查询订单
 private bool QueryOrder(string transaction_id)
 {
  WxPayData req = new WxPayData();
  req.SetValue("transaction_id", transaction_id);
  WxPayData res = WxPayApi.OrderQuery(req);
  if (res.GetValue("return_code").ToString() == "SUCCESS" &&
  res.GetValue("result_code").ToString() == "SUCCESS")
  {
  return true;
  }
  else
  {
  return false;
  }
 }