MSDN有一个样本。

using System;
using System.IO;
using System.Net;
using System.Text;

namespace Examples.System.Net
{
    public class WebRequestPostExample
    {
        public static void Main()
        {
            // Create a request using a URL that can receive a post. 
            WebRequest request = WebRequest.Create("http://www.contoso.com/PostAccepter.aspx");
            // Set the Method property of the request to POST.
            request.Method = "POST";
            // Create POST data and convert it to a byte array.
            string postData = "This is a test that posts this string to a Web server.";
            byte[] byteArray = Encoding.UTF8.GetBytes(postData);
            // Set the ContentType property of the WebRequest.
            request.ContentType = "application/x-www-form-urlencoded";
            // Set the ContentLength property of the WebRequest.
            request.ContentLength = byteArray.Length;
            // Get the request stream.
            Stream dataStream = request.GetRequestStream();
            // Write the data to the request stream.
            dataStream.Write(byteArray, 0, byteArray.Length);
            // Close the Stream object.
            dataStream.Close();
            // Get the response.
            WebResponse response = request.GetResponse();
            // Display the status.
            Console.WriteLine(((HttpWebResponse)response).StatusDescription);
            // Get the stream containing content returned by the server.
            dataStream = response.GetResponseStream();
            // Open the stream using a StreamReader for easy access.
            StreamReader reader = new StreamReader(dataStream);
            // Read the content.
            string responseFromServer = reader.ReadToEnd();
            // Display the content.
            Console.WriteLine(responseFromServer);
            // Clean up the streams.
            reader.Close();
            dataStream.Close();
            response.Close();
        }
    }
}

如果需要POST JSON消息体，可以使用以下方法。假设您有一个名为m的类实例。

string jsonMessage = JsonConvert.SerializeObject(m);

// Make POST call
using (HttpClient client = new HttpClient())
{
    HttpRequestMessage requestMessage = new
    HttpRequestMessage(HttpMethod.Post, "<url here>");
    requestMessage.Content = new StringContent(jsonMessage, Encoding.UTF8, "application/json");
    HttpResponseMessage response = client.SendAsync(requestMessage).Result;
    if (response.StatusCode == System.Net.HttpStatusCode.OK)
    {
        // Do something here
    }
}

执行HTTP GET和POST请求有几种方法:

---

方法A: HttpClient(首选)

支持。net Framework 4.5+， . net Standard 1.1+， . net Core 1.0+。

它是目前首选的方法，并且是异步的和高性能的。在大多数情况下使用内置版本，但对于非常老的平台，有一个NuGet包。

using System.Net.Http;

设置

建议为应用程序的生命周期实例化一个HttpClient并共享它，除非您有特定的理由不这样做。

private static readonly HttpClient client = new HttpClient();

请参阅HttpClientFactory以获得依赖注入解决方案。

---

帖子 var values = new Dictionary<string, string> ｛ {"thing1"， "hello"}， {"thing2"， "world"} }; var content = new FormUrlEncodedContent(values); var response = await client.PostAsync("http://www.example.com/recepticle.aspx"， content); var responseString =等待response.Content.ReadAsStringAsync(); 得到 var responseString = await client.GetStringAsync("http://www.example.com/recepticle.aspx");

---

方法B:第三方库

休息夏普

帖子 var client = new RestClient("http://example.com"); / /客户端。Authenticator =新的HttpBasicAuthenticator(用户名，密码); var request = new RestRequest("resource/{id}"); 请求。AddParameter(“thing1”、“你好”); 请求。AddParameter(“事件”、“世界”); 请求。AddHeader(“标题”、“价值”); 请求。AddFile(“文件”,路径); var response = client.Post(请求); var content = response.Content;//原始内容为字符串 var response2 = client.Post<Person>(request); var name = response2.Data.Name;

Flurl。Http

它是一个更新的库，拥有一个流畅的API，测试助手，在底层使用HttpClient，并且是可移植的。它可以通过NuGet获得。

    using Flurl.Http;

---

帖子 var responseString = await“http://www.example.com/recepticle.aspx” .PostUrlEncodedAsync(new {thing1 = "hello"， thing2 = "world"}) .ReceiveString (); 得到 var responseString = await“http://www.example.com/recepticle.aspx” .GetStringAsync ();

---

方法C: HttpWebRequest(不推荐用于新工作)

支持。net Framework 1.1+， . net Standard 2.0+， . net Core 1.0+。在。net Core中，它主要是为了兼容性——它包装了HttpClient，性能较差，并且不会获得新的特性。

using System.Net;
using System.Text;  // For class Encoding
using System.IO;    // For StreamReader

---

发布 var request = （HttpWebRequest）WebRequest.Create（“http://www.example.com/recepticle.aspx”）; var postData = “thing1=” + Uri.EscapeDataString（“hello”）; postData += “&thing2=” + Uri.EscapeDataString（“world”）; var data = Encoding.ASCII.GetBytes（postData）; 请求。方法 =“开机自检”; 请求。ContentType = “application/x-www-form-urlencoded”; 请求。内容长度 = 数据。长度; 使用 （var 流 = 请求。GetRequestStream（）） { 流。写入（数据， 0， 数据.长度）; } var response = （HttpWebResponse）request.获取响应（）; var responseString = new StreamReader（response.GetResponseStream（））。ReadToEnd（）; 获取 var request = （HttpWebRequest）WebRequest.Create（“http://www.example.com/recepticle.aspx”）; var response = （HttpWebResponse）request.获取响应（）; var responseString = new StreamReader（response.GetResponseStream（））。ReadToEnd（）;

---

方法D: WebClient(不推荐新作品)

这是一个HttpWebRequest的包装器。与HttpClient比较。

支持。NET Framework 1.1+， NET Standard 2.0+和。NET Core 2.0+。

在某些情况下…NET Framework 4.5-4.8)，如果你需要同步地做一个HTTP请求，WebClient仍然可以使用。

using System.Net;
using System.Collections.Specialized;

---

帖子 使用(var client = new WebClient()) ｛ var values = new NameValueCollection(); 值["thing1"] = "hello"; Values ["thing2"] = "world"; var response = client.UploadValues("http://www.example.com/recepticle.aspx"， values); var responseString = Encoding.Default.GetString(response); } 得到 使用(var client = new WebClient()) ｛ var responseString = client.DownloadString("http://www.example.com/recepticle.aspx"); }

简单的GET请求

using System.Net;

...

using (var wb = new WebClient())
{
    var response = wb.DownloadString(url);
}

简单的POST请求

using System.Net;
using System.Collections.Specialized;

...

using (var wb = new WebClient())
{
    var data = new NameValueCollection();
    data["username"] = "myUser";
    data["password"] = "myPassword";

    var response = wb.UploadValues(url, "POST", data);
    string responseInString = Encoding.UTF8.GetString(response);
}

这里有一些非常好的答案。让我发布一种不同的方法来设置你的头部与WebClient()。我还将向您展示如何设置API键。

        var client = new WebClient();
        string credentials = Convert.ToBase64String(Encoding.ASCII.GetBytes(userName + ":" + passWord));
        client.Headers[HttpRequestHeader.Authorization] = $"Basic {credentials}";
        //If you have your data stored in an object serialize it into json to pass to the webclient with Newtonsoft's JsonConvert
        var encodedJson = JsonConvert.SerializeObject(newAccount);

        client.Headers.Add($"x-api-key:{ApiKey}");
        client.Headers.Add("Content-Type:application/json");
        try
        {
            var response = client.UploadString($"{apiurl}", encodedJson);
            //if you have a model to deserialize the json into Newtonsoft will help bind the data to the model, this is an extremely useful trick for GET calls when you have a lot of data, you can strongly type a model and dump it into an instance of that class.
            Response response1 = JsonConvert.DeserializeObject<Response>(response);

到目前为止，我找到了简单的解决方案(一行程序，没有错误检查，没有等待响应):

(new WebClient()).UploadStringAsync(new Uri(Address), dataString);‏

请谨慎使用!