微信小程序支付功能的开发的时候坑比较多，不过对于钱的事谨慎也是好事。网上关于小程序支付的实例很多，但是大多多少有些问题，C#开发的更少。此篇文档的目的是讲开发过程中遇到的问题做一个备注，也方便其他开发的同学作为参考！

       1、首先建议把官方文档支付部分看上三遍，每个细节都不要放过，因为任何一个点和微信要求不符都会导致支付不成功。https://pay.weixin.qq.com/wiki/doc/api/wxa/wxa_api.php?chapter=3_1

      2、经过验证的微信支付功能，会需要一些商户号、支付秘钥等，不要搞混。

     3、经常遇到的是“签名错误”，请仔细看需要传送的xml参数及取值规则是否符合微信规则。微信有个验证工具可以验证发送的xml字段是否合法。

下面上代码：

web.config

    <add key="ConnectionString" value="server=127.0.0.1;database=;uid=sa;pwd="/>
    <add key="ConnectionString2" value="server=127.0.0.1;database=codematic2;uid=sa;pwd=1"/>
    <add key="appid" value=""/>//appid
    <add key="secret" value=""/>//小程序秘钥
    <add key="mch_id" value=""/>//商户号
    <add key="key" value=""/>//支付秘钥
    <add key="ip" value=""/>//服务器IP
    <add key="PayResulturl" value=""/>//微信返回接收信息的url地址
  </appSettings>

支付后台xiadan.ashx

<%@ WebHandler Language="C#" Class="xiadan" %>

using System;
using System.Web;
using System.Net;
using System.IO;
using System.Configuration;
using Maticsoft.Model;
using Maticsoft.BLL;
using System.Security.Cryptography;
using System.Text;
using System.Xml.Serialization;
using System.Xml;
using System.Collections.Generic;
using System.Data;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.Linq;
using Newtonsoft.Json;

public class xiadan : IHttpHandler
{

    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "text/plain";
        string openid = context.Request.Params["openid"];
        string ordertime = context.Request.Params["ordertime"];

        string appid = ConfigurationManager.AppSettings["appid"];
        string secret = ConfigurationManager.AppSettings["secret"];
        string key = ConfigurationManager.AppSettings["key"];
        string mch_id = ConfigurationManager.AppSettings["mch_id"];
        string ip = ConfigurationManager.AppSettings["ip"];
        string PayResulturl = ConfigurationManager.AppSettings["PayResulturl"];
        string roomid = context.Request.Params["roomid"];
        string aa = "-押金";////商品描述交易字段格式根据不同的应用场景按照以下格式：APP——需传入应用市场上的APP名字-实际商品名称，天天爱消除-游戏充值。

        string strcode = aa;
        byte[] buffer = Encoding.UTF8.GetBytes(strcode);
        string body = Encoding.UTF8.GetString(buffer, 0, buffer.Length);
        string totalfee = context.Request.Params["totalfee"];
        string output = "";
        if ((context.Request.Params["openid"] != null) && (context.Request.Params["openid"] != ""))
        {
            //OrderInfo order = new OrderInfo();

            //order.appid = appid;

            System.Random Random = new System.Random();



            var dic = new Dictionary<string, string>
{
    {"appid", appid},
    {"mch_id", mch_id},
    {"nonce_str", GetRandomString(20)/*Random.Next().ToString()*/},
    {"body",body},
    {"out_trade_no",roomid + DateTime.Now.ToString("yyyyMMddHHmmssfff") + Random.Next(999).ToString()},//商户自己的订单号码
    {"total_fee",totalfee},
    {"spbill_create_ip",ip},//服务器的IP地址
    {"notify_url",PayResulturl},//异步通知的地址，不能带参数
    {"trade_type","JSAPI" },
    {"openid",openid}
};
      //加入签名
            dic.Add("sign", GetSignString(dic));

            var sb = new StringBuilder();
            sb.Append("<xml>");


            foreach (var d in dic)
            {
                sb.Append("<" + d.Key + ">" + d.Value + "</" + d.Key + ">");
            }
            sb.Append("</xml>");
            var xml = new XmlDocument();
            //  xml.LoadXml(GetPostString("https://api.mch.weixin.qq.com/pay/unifiedorder", sb.ToString()));
            CookieCollection coo = new CookieCollection();
            Encoding en = Encoding.GetEncoding("UTF-8");

            HttpWebResponse response = CreatePostHttpResponse("https://api.mch.weixin.qq.com/pay/unifiedorder", sb.ToString(), en);
            //打印返回值
            Stream stream = response.GetResponseStream();   //获取响应的字符串流
            StreamReader sr = new StreamReader(stream); //创建一个stream读取流
            string html = sr.ReadToEnd();   //从头读到尾，放到字符串html
                                            //Console.WriteLine(html);
            xml.LoadXml(html);
            //对请求返回值 进行处理

            var root = xml.DocumentElement;

            DataSet ds = new DataSet();
            StringReader stram = new StringReader(html);
            XmlTextReader reader = new XmlTextReader(stram);
            ds.ReadXml(reader);
            string return_code = ds.Tables[0].Rows[0]["return_code"].ToString();
            if (return_code.ToUpper() == "SUCCESS")
            {
                //通信成功
                string result_code = ds.Tables[0].Rows[0]["result_code"].ToString();//业务结果
                if (result_code.ToUpper() == "SUCCESS")
                {
                    var res = new Dictionary<string, string>
{
    {"appId", appid},
    {"timeStamp", GetTimeStamp()},
    {"nonceStr", dic["nonce_str"]},
    {"package",  "prepay_id="+ds.Tables[0].Rows[0]["prepay_id"].ToString()},
    {"signType", "MD5"}
};

                    //在服务器上签名
                    res.Add("paySign", GetSignString(res));
                    // string signapp = res.ToString();
                    string signapp = JsonConvert.SerializeObject(res);
                    if ((context.Request.Params["openid"] != null) && (context.Request.Params["openid"] != ""))
                    { 
                    //存储订单信息
                    Maticsoft.Model.order_history oh = new Maticsoft.Model.order_history();
                    //oh.shop_id =
                    oh.room_id = Convert.ToInt32(roomid);
                    oh.pay_price = Convert.ToDecimal(totalfee);
                    oh.out_trade_no = dic["out_trade_no"];
                    oh.order_timestart = Convert.ToDateTime(ordertime);
                    oh.openid = openid;
                    oh.creating_date = DateTime.Now;

                    Maticsoft.BLL.order_history bll = new Maticsoft.BLL.order_history();
                    bll.Add(oh);

                }
                context.Response.Write(signapp);
            }
        }




    }
    context.Response.Write(output);
    }

public bool IsReusable
{
    get
    {
        return false;
    }
}

public string GetMd5Hash(String input)
{
    if (input == null)
    {
        return null;
    }

    MD5 md5Hash = MD5.Create();

    // 将输入字符串转换为字节数组并计算哈希数据  
    byte[] data = md5Hash.ComputeHash(Encoding.UTF8.GetBytes(input));

    // 创建一个 Stringbuilder 来收集字节并创建字符串  
    StringBuilder sBuilder = new StringBuilder();

    // 循环遍历哈希数据的每一个字节并格式化为十六进制字符串  
    for (int i = 0; i < data.Length; i++)
    {
        sBuilder.Append(data[i].ToString());
    }

    // 返回十六进制字符串  
    return sBuilder.ToString();
}
/// <summary>  
/// 对象序列化成 XML String  
/// </summary>  
public static string XmlSerialize<T>(T obj)
{
    string xmlString = string.Empty;
    XmlSerializer xmlSerializer = new XmlSerializer(typeof(T));
    using (MemoryStream ms = new MemoryStream())
    {
        xmlSerializer.Serialize(ms, obj);
        xmlString = Encoding.UTF8.GetString(ms.ToArray());
    }
    return xmlString;
}
/// <summary>
/// 从字符串里随机得到，规定个数的字符串.
/// </summary>
/// <param name="allChar"></param>
/// <param name="CodeCount"></param>
/// <returns></returns>
public static string GetRandomString(int CodeCount)
{
    string allChar = "1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,i,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z";
    string[] allCharArray = allChar.Split(\',\');
    string RandomCode = "";
    int temp = -1;
    Random rand = new Random();
    for (int i = 0; i < CodeCount; i++)
    {
        if (temp != -1)
        {
            rand = new Random(temp * i * ((int)DateTime.Now.Ticks));
        }
        int t = rand.Next(allCharArray.Length - 1);
        while (temp == t)
        {
            t = rand.Next(allCharArray.Length - 1);
        }
        temp = t;
        RandomCode += allCharArray[t];
    }

    return RandomCode;
}


public static string GetWebClientIp()
{
    string userIP = "IP";

    try
    {
        if (System.Web.HttpContext.Current == null
    || System.Web.HttpContext.Current.Request == null
    || System.Web.HttpContext.Current.Request.ServerVariables == null)
            return "";

        string CustomerIP = "";

        //CDN加速后取到的IP   
        CustomerIP = System.Web.HttpContext.Current.Request.Headers["Cdn-Src-Ip"];
        if (!string.IsNullOrEmpty(CustomerIP))
        {
            return CustomerIP;
        }

        CustomerIP = System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];


        if (!String.IsNullOrEmpty(CustomerIP))
            return CustomerIP;

        if (System.Web.HttpContext.Current.Request.ServerVariables["HTTP_VIA"] != null)
        {
            CustomerIP = System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
            if (CustomerIP == null)
                CustomerIP = System.Web.HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
        }
        else
        {
            CustomerIP = System.Web.HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];

        }

        if (string.Compare(CustomerIP, "unknown", true) == 0)
            return System.Web.HttpContext.Current.Request.UserHostAddress;
        return CustomerIP;
    }
    catch { }

    return userIP;
}




private static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
{
    return true; //总是接受   
}

public static HttpWebResponse CreatePostHttpResponse(string url, string datas, Encoding charset)
{
    HttpWebRequest request = null;
    //HTTPSQ请求
    ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
    request = WebRequest.Create(url) as HttpWebRequest;
    request.ProtocolVersion = HttpVersion.Version10;
    request.Method = "POST";
    request.ContentType = "application/x-www-form-urlencoded";

    //如果需要POST数据   
    //if (!(parameters == null || parameters.Count == 0))
    //{
    StringBuilder buffer = new StringBuilder();
    //int i = 0;
    //foreach (string key in parameters.Keys)
    //{
    //    if (i > 0)
    //    {
    //        buffer.AppendFormat("&{0}={1}", key, parameters[key]);
    //    }
    //    else
    //    {
    //        buffer.AppendFormat("{0}={1}", key, parameters[key]);
    //    }
    //    i++;
    //}
    buffer.AppendFormat(datas);
    byte[] data = charset.GetBytes(buffer.ToString());
    using (Stream stream = request.GetRequestStream())
    {
        stream.Write(data, 0, data.Length);
    }
    //}
    return request.GetResponse() as HttpWebResponse;
}


public string GetSignString(Dictionary<string, string> dic)
{
    string key = System.Web.Configuration.WebConfigurationManager.AppSettings["key"].ToString();//商户平台 API安全里面设置的KEY  32位长度
                                                                                                //排序
    dic = dic.OrderBy(d => d.Key).ToDictionary(d => d.Key, d => d.Value);
    //连接字段
    var sign = dic.Aggregate("", (current, d) => current + (d.Key + "=" + d.Value + "&"));
    sign += "key=" + key;
    //MD5
    // sign = System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sign, "MD5").ToUpper();
    System.Security.Cryptography.MD5 md5 = System.Security.Cryptography.MD5.Create();
    sign = BitConverter.ToString(md5.ComputeHash(Encoding.UTF8.GetBytes(sign))).Replace("-", null);
    return sign;
}


/// <summary>  
/// 获取时间戳  
/// </summary>  
/// <returns></returns>  
public static string GetTimeStamp()
{
    TimeSpan ts = DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, 0);
    return Convert.ToInt64(ts.TotalSeconds).ToString();
}

}

      微信返回信息接收后台页面notify_url.ashx

<%@ WebHandler Language="C#" Class="notify_url" %>

using System;
using System.Web;
using System.Collections.Generic;
using System.Data;
using System.IO;
using System.Text;
using System.Xml;
using System.Net;
public class notify_url : IHttpHandler
{
    public string return_result = "";
    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "text/plain";
        context.Response.Write("Hello World");


        String xmlData = getPostStr();//获取请求数据
        if (xmlData == "")
        {

        }
        else
        {
            var dic = new Dictionary<string, string>
{
    {"return_code", "SUCCESS"},
    {"return_msg","OK"}

};
            var sb = new StringBuilder();
            sb.Append("<xml>");


            foreach (var d in dic)
            {
                sb.Append("<" + d.Key + ">" + d.Value + "</" + d.Key + ">");
            }
            sb.Append("</xml>");





            //把数据重新返回给客户端
            DataSet ds = new DataSet();
            StringReader stram = new StringReader(xmlData);
            XmlTextReader datareader = new XmlTextReader(stram);
            ds.ReadXml(datareader);
            if (ds.Tables[0].Rows[0]["return_code"].ToString() == "SUCCESS")
            {


                string wx_appid = "";//微信开放平台审核通过的应用APPID
                string wx_mch_id = "";//微信支付分配的商户号

                string wx_nonce_str = "";// 	随机字符串，不长于32位
                string wx_sign = "";//签名，详见签名算法
                string wx_result_code = "";//SUCCESS/FAIL

                string wx_return_code = "";
                string wx_openid = "";//用户在商户appid下的唯一标识
                string wx_is_subscribe = "";//用户是否关注公众账号，Y-关注，N-未关注，仅在公众账号类型支付有效
                string wx_trade_type = "";// 	APP
                string wx_bank_type = "";// 	银行类型，采用字符串类型的银行标识，银行类型见银行列表
                string wx_fee_type = "";// 	货币类型，符合ISO4217标准的三位字母代码，默认人民币：CNY，其他值列表详见货币类型


                string wx_transaction_id = "";//微信支付订单号
                string wx_out_trade_no = "";//商户系统的订单号，与请求一致。
                string wx_time_end = "";// 	支付完成时间，格式为yyyyMMddHHmmss，如2009年12月25日9点10分10秒表示为20091225091010。其他详见时间规则
                int wx_total_fee = -1;// 	订单总金额，单位为分
                int wx_cash_fee = -1;//现金支付金额订单现金支付金额，详见支付金额


                #region  数据解析
                //列 是否存在
                string signstr = "";//需要前面的字符串
                                    //wx_appid
                if (ds.Tables[0].Columns.Contains("appid"))
                {
                    wx_appid = ds.Tables[0].Rows[0]["appid"].ToString();
                    if (!string.IsNullOrEmpty(wx_appid))
                    {
                        signstr += "appid=" + wx_appid;
                    }
                }

                //wx_bank_type
                if (ds.Tables[0].Columns.Contains("bank_type"))
                {
                    wx_bank_type = ds.Tables[0].Rows[0]["bank_type"].ToString();
                    if (!string.IsNullOrEmpty(wx_bank_type))
                    {
                        signstr += "&bank_type=" + wx_bank_type;
                    }
                }
                //wx_cash_fee
                if (ds.Tables[0].Columns.Contains("cash_fee"))
                {
                    wx_cash_fee = Convert.ToInt32(ds.Tables[0].Rows[0]["cash_fee"].ToString());

                    signstr += "&cash_fee=" + wx_cash_fee;
                }

                //wx_fee_type
                if (ds.Tables[0].Columns.Contains("fee_type"))
                {
                    wx_fee_type = ds.Tables[0].Rows[0]["fee_type"].ToString();
                    if (!string.IsNullOrEmpty(wx_fee_type))
                    {
                        signstr += "&fee_type=" + wx_fee_type;
                    }
                }

                //wx_is_subscribe
                if (ds.Tables[0].Columns.Contains("is_subscribe"))
                {
                    wx_is_subscribe = ds.Tables[0].Rows[0]["is_subscribe"].ToString();
                    if (!string.IsNullOrEmpty(wx_is_subscribe))
                    {
                        signstr += "&is_subscribe=" + wx_is_subscribe;
                    }
                }

                //wx_mch_id
                if (ds.Tables[0].Columns.Contains("mch_id"))
                {
                    wx_mch_id = ds.Tables[0].Rows[0]["mch_id"].ToString();
                    if (!string.IsNullOrEmpty(wx_mch_id))
                    {
                        signstr += "&mch_id=" + wx_mch_id;
                    }
                }

                //wx_nonce_str
                if (ds.Tables[0].Columns.Contains("nonce_str"))
                {
                    wx_nonce_str = ds.Tables[0].Rows[0]["nonce_str"].ToString();
                    if (!string.IsNullOrEmpty(wx_nonce_str))
                    {
                        signstr += "&nonce_str=" + wx_nonce_str;
                    }
                }

                //wx_openid
                if (ds.Tables[0].Columns.Contains("openid"))
                {
                    wx_openid = ds.Tables[0].Rows[0]["openid"].ToString();
                    if (!string.IsNullOrEmpty(wx_openid))
                    {
                        signstr += "&openid=" + wx_openid;
                    }
                }

                //wx_out_trade_no
                if (ds.Tables[0].Columns.Contains("out_trade_no"))
                {
                    wx_out_trade_no = ds.Tables[0].Rows[0]["out_trade_no"].ToString();
                    if (!string.IsNullOrEmpty(wx_out_trade_no))
                    {
                        signstr += "&out_trade_no=" + wx_out_trade_no;
                    }
                }

                //wx_result_code 
                if (ds.Tables[0].Columns.Contains("result_code"))
                {
                    wx_result_code = ds.Tables[0].Rows[0]["result_code"].ToString();
                    if (!string.IsNullOrEmpty(wx_result_code))
                    {
                        signstr += "&result_code=" + wx_result_code;
                    }
                }

                //wx_result_code 
                if (ds.Tables[0].Columns.Contains("return_code"))
                {
                    wx_return_code = ds.Tables[0].Rows[0]["return_code"].ToString();
                    if (!string.IsNullOrEmpty(wx_return_code))
                    {
                        signstr += "&return_code=" + wx_return_code;
                    }
                }

                //wx_sign 
                if (ds.Tables[0].Columns.Contains("sign"))
                {
                    wx_sign = ds.Tables[0].Rows[0]["sign"].ToString();
                    //if (!string.IsNullOrEmpty(wx_sign))
                    //{
                    //    signstr += "&sign=" + wx_sign;
                    //}
                }

                //wx_time_end
                if (ds.Tables[0].Columns.Contains("time_end"))
                {
                    wx_time_end = ds.Tables[0].Rows[0]["time_end"].ToString();
                    if (!string.IsNullOrEmpty(wx_time_end))
                    {
                        signstr += "&time_end=" + wx_time_end;
                    }
                }

                //wx_total_fee
                if (ds.Tables[0].Columns.Contains("total_fee"))
                {
                    wx_total_fee = Convert.ToInt32(ds.Tables[0].Rows[0]["total_fee"].ToString());

                    signstr += "&total_fee=" + wx_total_fee;
                }

                //wx_trade_type
                if (ds.Tables[0].Columns.Contains("trade_type"))
                {
                    wx_trade_type = ds.Tables[0].Rows[0]["trade_type"].ToString();
                    if (!string.IsNullOrEmpty(wx_trade_type))
                    {
                        signstr += "&trade_type=" + wx_trade_type;
                    }
                }

                //wx_transaction_id
                if (ds.Tables[0].Columns.Contains("transaction_id"))
                {
                    wx_transaction_id = ds.Tables[0].Rows[0]["transaction_id"].ToString();
                    if (!string.IsNullOrEmpty(wx_transaction_id))
                    {
                        signstr += "&transaction_id=" + wx_transaction_id;
                    }
                }

                #endregion

                //追加key 密钥
                signstr += "&key=" + System.Web.Configuration.WebConfigurationManager.AppSettings["key"].ToString();
                //签名正确
                string orderStrwhere = "ordernumber=\'" + wx_out_trade_no + "\'";



                if (wx_sign == System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(signstr, "MD5").ToUpper())
                {
                    //签名正确   处理订单操作逻辑


                }
                else
                {
                    //追加备注信息

                }

            }
            else
            {
                // 返回信息，如非空，为错误原因  签名失败 参数格式校验错误
                string return_msg = ds.Tables[0].Rows[0]["return_msg"].ToString();

            }


            return_result = sb.ToString();
        }
    }


    public bool IsReusable
    {
        get
        {
            return false;
        }
    }

    //获得Post过来的数据
    public string getPostStr()
    {
        Int32 intLen = Convert.ToInt32(System.Web.HttpContext.Current.Request.InputStream.Length);
        byte[] b = new byte[intLen];
        System.Web.HttpContext.Current.Request.InputStream.Read(b, 0, intLen);
        return System.Text.Encoding.UTF8.GetString(b);
    }
}