使用HttpClient和WebRequest时POST一个对象的写法

【一】步骤：

1）将对象转化为Json字符串。

2）将Json字符串编码为byte数组。

3）设置传输对象（WebRequest或者HttpClient）的ContentType是"application/json"。

4）设置传输对象的ContentLength=Byte数组的长度。

5）开始传输

6）获取JSON结果：

【二】示例代码：

【对于WebRequest而言】

static void SendByWebRequesttoApi()
        {
            WebRequest req = WebRequest.Create("http://localhost:15203/api/ApiDefault");
            var stu = new Student { ID = 1, Name = "董玮" };
            string jsonString = JsonConvert.SerializeObject(stu);
            byte[] objectContent = Encoding.UTF8.GetBytes(jsonString);
            req.ContentLength = objectContent.Length;
            req.ContentType = "application/json";
            req.Method = "POST";
            using (var stream = req.GetRequestStream())
            {
                stream.Write(objectContent, 0, objectContent.Length);
                stream.Close();
            }

            var resp = req.GetResponse();
            using (StreamReader sr = new StreamReader(resp.GetResponseStream()))
            {
                string s = sr.ReadToEnd();
                System.Console.WriteLine(s);
            }
        }

【对于HttpClient而言】

static void SendByHttpClienttoApi()
        {
            var stu = new { ID = 1, Name = "董玮" };
            using (var client = new HttpClient())
            {
                string jsonString = JsonConvert.SerializeObject(stu);
                byte[] bytes = Encoding.UTF8.GetBytes(jsonString);
                using (StreamContent sc = new StreamContent(new MemoryStream(bytes)))
                {
                    sc.Headers.ContentLength = bytes.Length;
                    sc.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
                    var result = client.PostAsync("http://localhost:15203/api/ApiDefault", sc).Result;
                    var objectResult = JsonConvert.DeserializeObject<Student>(result.Content.ReadAsStringAsync().Result);
                }

            }
        }

另外注意，以上是针对WebApi（WebApi默认是JSON格式数据传输）。如果是MVC的模式，那么默认是表单形式传输。因此：

 static void SendByWebRequesttoMVC()
        {
            WebRequest req = WebRequest.Create("http://localhost:15203/Default/DoGetStudent");
            var htmlFormPost = "ID=1&Name=董玮";
            byte[] objectContent = Encoding.UTF8.GetBytes(htmlFormPost);
            req.ContentLength = objectContent.Length;
            req.ContentType = "application/x-www-form-urlencoded";   //必须写！
            req.Method = "POST";
            using (var stream = req.GetRequestStream())
            {
                stream.Write(objectContent, 0, objectContent.Length);
                stream.Close();
            }

            var resp = req.GetResponse();
            using (StreamReader sr = new StreamReader(resp.GetResponseStream()))
            {
                string s = sr.ReadToEnd();
                System.Console.WriteLine(s);
            }
        }

在HttpClient中，把StreamContent改为FormUrlEncodedContent，传入一个Dictionary<string,string>对象即可：

 static void SendByHttpClienttoMVC()
        {
            using (var client = new HttpClient())
            {
                FormUrlEncodedContent fc = new FormUrlEncodedContent(new Dictionary<string, string>() { { "ID", "1" }, { "Name", "董玮" } });
                var result = client.PostAsync("http://localhost:15203/Default/DoGetStudent", fc).Result;
                System.Console.WriteLine(result.Content.ReadAsStringAsync().Result);
            }
        }

原文地址：https://www.cnblogs.com/coce/p/9721034.html