asp.net 接入微信公众平台，回复消息，解决乱码问题

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Text;
using System.Security.Cryptography;
using System.IO;
using System.Xml;
using System.Text.RegularExpressions;

namespace ServiceAndLock
{
    /// <summary>
    /// wxapi 的摘要说明
    /// </summary>
    public class wxapi : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            if (context.Request.HttpMethod.ToUpper() == "GET")
            {
                //string msg ="测试";
                //context.Response.Write(msg);
                //context.Response.End();
                // 微信加密签名  
                string signature = context.Request.QueryString["signature"];
                // 时间戳  
                string timestamp = context.Request.QueryString["timestamp"];
                // 随机数  
                string nonce = context.Request.QueryString["nonce"];
                // 随机字符串  
                string echostr = context.Request.QueryString["echostr"];
                if (CheckSignature(signature, timestamp, nonce))
                {
                    context.Response.Write(echostr);
                }
            }
            else if (context.Request.HttpMethod.ToUpper() == "POST")
            {
                //接收消息，根据消息回复
                RequestX(context);
            }
        }
        /// <summary>
        /// 将原始字串转换为格式为&#....;&#....
        /// </summary>
        /// <param name="srcText"></param>
        /// <returns></returns>
        private string StringToISO_8859_1(string srcText)
        {
            string dst = "";
            char[] src = srcText.ToCharArray();
            for (int i = 0; i < src.Length; i++)
            {
                string str = @"&#" + (int)src[i] + ";";
                dst += str;
            }
            return dst;
        }
        /// <summary>
        /// 将字串&#....;&#....;格式字串转换为原始字符串
        /// </summary>
        /// <param name="srcText"></param>
        /// <returns></returns>
        private string ISO_8859_1ToString(string srcText)
        {
            string dst = "";
            string[] src = srcText.Split(';');

            for (int i = 0; i < src.Length; i++)
            {
                if (src[i].Length > 0)
                {
                    string str = ((char)int.Parse(src[i].Substring(2))).ToString();
                    dst += str;
                }
            }
            return dst;
        }
        /// <summary>
        /// 验证签名
        /// </summary>
        /// <param name="signature"></param>
        /// <param name="timestamp"></param>
        /// <param name="nonce"></param>
        /// <returns></returns>
        public static bool CheckSignature(String signature, String timestamp, String nonce)
        {
            String[] arr = new String[] { "123456", timestamp, nonce };
            // 将token、timestamp、nonce三个参数进行字典序排序  
            Array.Sort<String>(arr);
            StringBuilder content = new StringBuilder();
            for (int i = 0; i < arr.Length; i++)
            {
                content.Append(arr[i]);
            }
            String tmpStr = SHA1_Encrypt(content.ToString());
            // 将sha1加密后的字符串可与signature对比，标识该请求来源于微信  
            return tmpStr != null ? tmpStr.Equals(signature) : false;
        }

        /// <summary>
        /// 使用缺省密钥给字符串加密
        /// </summary>
        /// <param name="Source_String"></param>
        /// <returns></returns>
        public static string SHA1_Encrypt(string Source_String)
        {
            byte[] StrRes = Encoding.Default.GetBytes(Source_String);
            HashAlgorithm iSHA = new SHA1CryptoServiceProvider();
            StrRes = iSHA.ComputeHash(StrRes);
            StringBuilder EnText = new StringBuilder();
            foreach (byte iByte in StrRes)
            {
                EnText.AppendFormat("{0:x2}", iByte);
            }
            return EnText.ToString();
        }
        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
        public void RequestX(HttpContext context)
        {
            wxmessage wx = GetWxMessage(context);
            string res = "";
            //新用户添加
            if (!string.IsNullOrEmpty(wx.EventName) && wx.EventName.Trim() == "subscribe")
            {
                string content = "";
                content = "/:rose123324324欢迎关注测试帐号/:rose\n聊天请回复你好“x”\n无聊时候还可以找我聊聊天哦！";
                res = sendTextMessage(wx, content);
            }
            else
            {
                bool sendJoke = false;
                //看笑话
                List<string> xhList = new List<string>() { "x", "笑话", "笑話" };
                foreach (string item in xhList)
                {
                    if (wx.Content.Trim().ToLower().Contains(item))
                    {
                        sendJoke = true;
                        break;
                    }
                }
                if (sendJoke)
                {
                    string title = string.Format("编号{0}:{1}\n-----------------\n", "01", "测试回复");
                    string content = "333333测试回复内容";
                    if (content.Length > 300)
                    {
                        content = GetSubString(content, 300) + "\n-----------------\n点击连接阅读全文：URL";

                    }
                    res = sendTextMessage(wx, title + content);
                }
                //未知情况
                if (res == "")
                {
                    string content = "/:,@-D113333啊哦，你在说什么？\n你可以按照下面的格式告诉我：\n问：你说的话 答：你想让我说什么\n看笑话请直接回复“x”！";
                    res = sendTextMessage(wx, content);
                }
            }
            context.Response.HeaderEncoding = System.Text.Encoding.UTF8;
            context.Response.ContentEncoding = System.Text.Encoding.UTF8;
            context.Response.Charset = "utf-8"; 
            //context.Response.Write(Encoding.UTF8.GetString(Encoding.Default.GetBytes(res)));
           
            context.Response.Write(res);
        }
        /// <summary>
        /// 截取字符串
        /// </summary>
        /// <param name="content"></param>
        /// <param name="length"></param>
        /// <returns></returns>
        private string GetSubString(string content, int length)
        {
            if (content.Length >= length)
            {
                return content.Substring(0, length);
            }
            else
            {
                return content;
            }
        }

        /// <summary>
        /// 发送文字消息
        /// </summary>
        /// <param name="wx">获取的收发者信息</param>
        /// <param name="content">笑话内容</param>
        /// <returns></returns>
        private string sendTextMessage(wxmessage wx, string content)
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("<xml><ToUserName><![CDATA[{0}]]></ToUserName>", wx.FromUserName);
            sb.AppendFormat("<FromUserName><![CDATA[{0}]]></FromUserName>", wx.ToUserName);
            sb.AppendFormat("<CreateTime>{0}</CreateTime>", DateTime.Now);
            sb.AppendFormat("<MsgType><![CDATA[text]]></MsgType>");
            sb.AppendFormat("<Content><![CDATA[{0}]]></Content>", content);
            sb.AppendFormat("</xml>");
            return sb.ToString();
        }

        /// <summary>
        /// 发送图文消息
        /// </summary>
        /// <param name="wx">获取的收发者信息</param>
        /// <param name="joke">笑话信息</param>
        /// <returns></returns>
        private string sendPictureMessage(wxmessage wx)
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("<xml><ToUserName><![CDATA[{0}]]></ToUserName>", wx.FromUserName);
            sb.AppendFormat("<FromUserName><![CDATA[{0}]]></FromUserName>", wx.ToUserName);
            sb.AppendFormat("<CreateTime>{0}</CreateTime>", DateTime.Now);
            sb.AppendFormat("<MsgType><![CDATA[news]]></MsgType><Content><![CDATA[]]></Content>");
            sb.AppendFormat("<ArticleCount>1</ArticleCount>");
            sb.AppendFormat("<Articles><item>");
            sb.AppendFormat("<Title><![CDATA[{0}]]></Title>", "标题");
            sb.AppendFormat("<Description><![CDATA[{0}]]></Description>", "说明文字");
            sb.AppendFormat("<PicUrl><![CDATA[{0}]]></PicUrl>", "图片地址");
            sb.AppendFormat("<Url><![CDATA[{0}]]></Url>", "连接地址");
            sb.AppendFormat("</item></Articles><FuncFlag>0</FuncFlag></xml>");
            return sb.ToString();
        }

        /// <summary>
        /// 获取请求过来的微信信息
        /// </summary>
        /// <returns></returns>
        private wxmessage GetWxMessage(HttpContext context)
        {
            wxmessage wx = new wxmessage();
            StreamReader str = new StreamReader(context.Request.InputStream, System.Text.Encoding.UTF8);
            XmlDocument xml = new XmlDocument();
            xml.Load(str);
            wx.ToUserName = xml.SelectSingleNode("xml").SelectSingleNode("ToUserName").InnerText;
            wx.FromUserName = xml.SelectSingleNode("xml").SelectSingleNode("FromUserName").InnerText;
            wx.MsgType = xml.SelectSingleNode("xml").SelectSingleNode("MsgType").InnerText;
            if (wx.MsgType.Trim() == "text")
            {
                wx.Content = xml.SelectSingleNode("xml").SelectSingleNode("Content").InnerText;
            }
            if (wx.MsgType.Trim() == "event")
            {
                wx.EventName = xml.SelectSingleNode("xml").SelectSingleNode("Event").InnerText;
            }
            return wx;
        }

    }
    //自定义一个微信消息实体类
    class wxmessage
    {
        public string FromUserName { get; set; }
        public string ToUserName { get; set; }
        public string MsgType { get; set; }
        public string EventName { get; set; }
        public string Content { get; set; }
    }
}

公众号开发者中心，设置的url，即以上内容，解决乱码是：

context.Response.HeaderEncoding = System.Text.Encoding.UTF8;
            context.Response.ContentEncoding = System.Text.Encoding.UTF8;
            context.Response.Charset = "utf-8"; 

接入url，走的是get方法，回复消息走的是post方法