程式碼：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    public static class HttpRequestHelper
    {
        public delegate int handleAsync(string str);
        /// <summary>
        /// Http Get Request
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        public static string HttpGetRequest(string url)
        {
            string strGetResponse = string.Empty;
            try
            {
                var getRequest = CreateHttpRequest(url, "GET");
                var getResponse = getRequest.GetResponse() as HttpWebResponse;
                strGetResponse = GetHttpResponse(getResponse, "GET");
            }
            catch (Exception ex)
            {
                strGetResponse = ex.Message;
            }
            return strGetResponse;
        }

        /// <summary>
        /// Http Get Request Async
        /// </summary>
        /// <param name="url"></param>
        public static async void HttpGetRequestAsync(string url)
        {
            string strGetResponse = string.Empty;
            try
            {
                var getRequest = CreateHttpRequest(url, "GET");
                var getResponse = await getRequest.GetResponseAsync() as HttpWebResponse;
                strGetResponse = GetHttpResponse(getResponse, "GET");
            }
            catch (Exception ex)
            {
                strGetResponse = ex.Message;
            }
            Console.WriteLine("reslut:" + strGetResponse);
            //return strGetResponse;
        }

        /// <summary>
        /// Http Post Request
        /// </summary>
        /// <param name="url"></param>
        /// <param name="postJsonData"></param>
        /// <returns></returns>
        public static string HttpPostRequest(string url, string postJsonData)
        {
            string strPostReponse = string.Empty;
            try
            {
                var postRequest = CreateHttpRequest(url, "POST", postJsonData);
                var postResponse = postRequest.GetResponse() as HttpWebResponse;
                strPostReponse = GetHttpResponse(postResponse, "POST");
            }
            catch (Exception ex)
            {
                strPostReponse = ex.Message;
            }
            return strPostReponse;
        }

        /// <summary>
        /// Http Post Request Async
        /// </summary>
        /// <param name="url"></param>
        /// <param name="postJsonData"></param>
        public static async void HttpPostRequestAsync(string url, string postData, handleAsync ha=null)
        {
            string strPostReponse = string.Empty;
            try
            {
                var postRequest = CreateHttpRequest(url, "POST", postData);
                var postResponse = await postRequest.GetResponseAsync() as HttpWebResponse;
                strPostReponse = GetHttpResponse(postResponse, "POST");
            }
            catch (Exception ex)
            {
                strPostReponse = ex.Message;
            }
            if (strPostReponse != "true")
            {
                //Console.WriteLine("--> reslut : " + strPostReponse);
                //Console.WriteLine(postData);

                if(null != ha)
                {
                    ha(strPostReponse);
                }
            }
        }

        public static string HttpUploadFile(string url, int timeOut, string fileKeyName, string filePath, Dictionary<string, string> list)
        {
            string responseContent;
            var memStream = new MemoryStream();
            var webRequest = (HttpWebRequest)WebRequest.Create(url);
            // 邊界符
            var boundary = "---------------" + DateTime.Now.Ticks.ToString("x");//日期的16進位制字串
            // 邊界符
            var beginBoundary = Encoding.ASCII.GetBytes("--" + boundary + "\r\n");
            // 最後的結束符
            var endBoundary = Encoding.ASCII.GetBytes("--" + boundary + "--\r\n");

            // 設定屬性
            webRequest.Method = "POST";
            webRequest.Timeout = timeOut;
            webRequest.ContentType = "multipart/form-data; boundary=" + boundary;

            // 寫入檔案----------1.--------------
            // 獲取檔名稱路徑最後一級，以\/分級，不分級則取全路徑為檔名
            int start = filePath.LastIndexOf("/");
            if(-1 == start)
            {
                start = filePath.LastIndexOf("\\");

                if(-1 == start)
                {
                    start = 0;
                }
            }
            string filename = filePath.Substring(start + 1);
            string filePartHeader = "Content-Disposition: form-data; name=\"{0}\"; filename=" + filename + "\r\n" + "Content-Type: application/octet-stream\r\n\r\n";
            var header = string.Format(filePartHeader, fileKeyName, filePath);
            Console.WriteLine(header);

            var headerbytes = Encoding.UTF8.GetBytes(header);
            memStream.Write(beginBoundary, 0, beginBoundary.Length);
            memStream.Write(headerbytes, 0, headerbytes.Length);

            // 獲取檔案流
            var fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
            var buffer = new byte[1024];
            int bytesRead; // =0

            // 檔案流寫入緩衝區
            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
            {
                memStream.Write(buffer, 0, bytesRead);
            }

            // 檔案後面要有換行
            string stringKeyHeader = "\r\n--" + boundary + "\r\nContent-Disposition: form-data; name=\"{0}\"\r\n\r\n{1}\r\n";
            // 遍歷引數，傳輸資料的編碼集----------- 2 -------------------
            foreach (var item in list)
            {   // 
                var dataByte = Encoding.UTF8.GetBytes(string.Format(stringKeyHeader, item.Key, item.Value));
                memStream.Write(dataByte, 0, dataByte.Length);
            }

            // 寫入最後的結束邊界符------------ 3.-------------------------
            memStream.Write(endBoundary, 0, endBoundary.Length);

            webRequest.ContentLength = memStream.Length;

            var requestStream = webRequest.GetRequestStream();

            memStream.Position = 0;
            var tempBuffer = new byte[memStream.Length];
            memStream.Read(tempBuffer, 0, tempBuffer.Length);
            memStream.Close();

            requestStream.Write(tempBuffer, 0, tempBuffer.Length);
            requestStream.Close();

            // 響應 ------------------- 4.-----------------------------------
            var httpWebResponse = (HttpWebResponse)webRequest.GetResponse();

            using (var httpStreamReader = new StreamReader(httpWebResponse.GetResponseStream(), Encoding.GetEncoding("utf-8")))
            {
                responseContent = httpStreamReader.ReadToEnd();
            }

            fileStream.Close();
            httpWebResponse.Close();
            webRequest.Abort();

            return responseContent;
        }

        private static HttpWebRequest CreateHttpRequest(string url, string requestType, string strJson="")
        {
            HttpWebRequest request = null;
            const string get = "GET";
            const string post = "POST";
            if (string.Equals(requestType, get, StringComparison.OrdinalIgnoreCase))
            {
                request = CreateGetHttpWebRequest(url);
            }
            if (string.Equals(requestType, post, StringComparison.OrdinalIgnoreCase))
            {
                request = CreatePostHttpWebRequest(url, strJson);
            }
            return request;
        }

        private static HttpWebRequest CreateGetHttpWebRequest(string url)
        {
            var getRequest = HttpWebRequest.Create(url) as HttpWebRequest;
            getRequest.Method = "GET";
            getRequest.Timeout = 5000;
            getRequest.ContentType = "text/html;charset=UTF-8";
            getRequest.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
            return getRequest;
        }

        private static HttpWebRequest CreatePostHttpWebRequest(string url, string postData)
        {
            var postRequest = HttpWebRequest.Create(url) as HttpWebRequest;
            postRequest.KeepAlive = false;
            postRequest.Timeout = 5000;
            postRequest.Method = "POST";
            postRequest.ContentType = "application/x-www-form-urlencoded";
            postRequest.ContentLength = postData.Length;
            postRequest.AllowWriteStreamBuffering = false;
            StreamWriter writer = new StreamWriter(postRequest.GetRequestStream(), Encoding.ASCII);
            writer.Write(postData);
            writer.Flush();
            return postRequest;
        }

        private static string GetHttpResponse(HttpWebResponse response, string requestType)
        {
            var responseResult = "";
            const string post = "POST";
            string encoding = "UTF-8";
            if (string.Equals(requestType, post, StringComparison.OrdinalIgnoreCase))
            {
                encoding = response.ContentEncoding;
                if (encoding == null || encoding.Length < 1)
                {
                    encoding = "UTF-8";
                }
            }
            using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding(encoding)))
            {
                responseResult = reader.ReadToEnd();
            }
            return responseResult;
        }

        private static string GetHttpResponseAsync(HttpWebResponse response, string requestType)
        {
            var responseResult = "";
            const string post = "POST";
            string encoding = "UTF-8";
            if (string.Equals(requestType, post, StringComparison.OrdinalIgnoreCase))
            {
                encoding = response.ContentEncoding;
                if (encoding == null || encoding.Length < 1)
                {
                    encoding = "UTF-8";
                }
            }
            using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding(encoding)))
            {
                responseResult = reader.ReadToEnd();
            }
            return responseResult;
        }

        //dictionary轉http get引數
        public static string DictoryToGetParam(Dictionary<string, string> dict)
        {
            string param = "";

            foreach(KeyValuePair<string, string> kv in dict)
            {
                param += kv.Key + '=' + kv.Value + '&';
            }

            if('&' == param[param.Length - 1])
            {
                param = param.Substring(0, param.Length - 1);
            }

            return param;
        }
    }
}
 

同步呼叫

        //同步http post
        static void testHttp()
        {
            var postUrl = "http://yoururl";
            Dictionary<string, string> postData = new Dictionary<string, string>();
 
            postData.Add("userID", "100000048");
            postData.Add("gradeID", "1");
 
            // 自己實現的http請求
            string postStr = HttpRequestHelper.DictoryToGetParam(postData);
 
            var repose = HttpRequestHelper.HttpPostRequest(postUrl, postStr);
            Console.WriteLine(repose);
        }
 

非同步呼叫

        static void testHttpAsync()
        {
            var postUrl = "http://yoururl";
            Dictionary<string, string> postData = new Dictionary<string, string>();
 
            postData.Add("userID", "100000048");
            postData.Add("gradeID", "1");

            string postStr = HttpRequestHelper.DictoryToGetParam(postData);


            //類中static回撥函式handlePostAsync
            HttpRequestHelper.HttpPostRequestAsync(getUrl, postStr, handlePostAsync);

            Console.WriteLine("http post async done");

            Console.Read();
        }

        //回撥函式
        static int handlePostAsync(string str)
        {
            Console.WriteLine("handle post Async : " + str);
            return 0;
        }
 

單檔案上傳帶引數

        static void testFileUpload()
        {
           var postUrl = "http://yoururl";
            Dictionary<string, string> postData = new Dictionary<string, string>();
 
            postData.Add("userID", "100000048");
            postData.Add("gradeID", "1");

            string returnData = HttpRequestHelper.HttpUploadFile(postUrl, 12000, "qrcode_image", "D://0//huojian.png", postData);

            Console.WriteLine(returnData);

            Console.Read();

        }