业务需求：

客户想要一个停车优惠券的功能，需要用户微信扫描后，自动跳转到小程序中，首先明确一点，这个操作是需要调微信接口的，下面我们来实现下吧

微信开发文档：
获取不限制的小程序码

  //code为优惠券码，唯一值
      public void CreateXcxQrCode(string code)
        {
            try
            {
                //首先建立文件夹
                string strDirPath = System.AppDomain.CurrentDomain.BaseDirectory + "ParkingCouponQrCoderImg"; 
                    if (!Directory.Exists(strDirPath))
                    {
                        Directory.CreateDirectory(strDirPath);
                    } 
//这里需要使用小程序的appid及appsecret ，用户获取access_token
                        string URL = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=" + _appid + "&secret=" + appsecret + "";
                        string Date2 = HttpGet(URL);
                        Newtonsoft.Json.Linq.JObject _jObject = Newtonsoft.Json.Linq.JObject.Parse(Date2);
                        string access_token = _jObject["access_token"].ToString();
                        string page = "pages/car/carindex";//跳转的小程序路径
                        string width = "280";//二维码大小
                        string _url = "https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=" + access_token;
                        System.Net.HttpWebRequest request;
                        request = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(_url);
                        request.Method = "POST";
                        request.ContentType = "application/json;charset=UTF-8";
//这里是参数
                        string scene = "index=0&code=" + code;
                        string options = "{\"scene\":\"" + scene + "\",\"page\":\"" + page + "\",\"width\":\"" + width + "\"}";
                        byte[] payload;
                        payload = System.Text.Encoding.UTF8.GetBytes(options);
                        request.ContentLength = payload.Length;
                        System.IO.Stream writer = request.GetRequestStream();
                        writer.Write(payload, 0, payload.Length);
                        writer.Close();
                        System.Net.HttpWebResponse response;
                        response = (System.Net.HttpWebResponse)request.GetResponse();
                        System.IO.Stream s;
                        s = response.GetResponseStream();
                        byte[] val = StreamToBytes(s);
                        string strdir_path=  strDirPath +"\\"+code + ".png";
                        System.IO.File.WriteAllBytes(strdir_path, val);
                        s.Dispose();
                        writer.Dispose();
                     string path = string.Format("/ParkingCouponQrCoderImg/{0}.png", code);
                      //之后就是将path 更新进数据库了
                
            }
            catch (System.Exception ex)
            {
                throw;
            }
        }       if (!Directory.Exists(strDirPath))
                {
                    Directory.CreateDirectory(strDirPath);
                }
        public  byte[] StreamToBytes(System.IO.Stream stream)
        {
            List<byte> bytes = new List<byte>();
            int temp = stream.ReadByte();
            while (temp != -1)
            {
                bytes.Add((byte)temp);
                temp = stream.ReadByte();
            }
            return bytes.ToArray();
        }