最简单的方法是使用StringContent，使用JSON对象的JSON表示形式。

httpClient.Post(
    "",
    new StringContent(
        myObject.ToString(),
        Encoding.UTF8,
        "application/json"));

如果使用Newtonsoft。Json:

using Newtonsoft.Json;
using System.Net.Http;
using System.Text;

public static class Extensions
{
    public static StringContent AsJson(this object o)
        => new StringContent(JsonConvert.SerializeObject(o), Encoding.UTF8, "application/json");
}

例子:

var httpClient = new HttpClient();
var url = "https://www.duolingo.com/2016-04-13/login?fields=";
var data = new { identifier = "username", password = "password" };
var result = await httpClient.PostAsync(url, data.AsJson())

最简单的方法是使用StringContent，使用JSON对象的JSON表示形式。

httpClient.Post(
    "",
    new StringContent(
        myObject.ToString(),
        Encoding.UTF8,
        "application/json"));

我花了好几个小时才解出来。 但是@anthls anwser救了我的命。

var data = new StringContent(JsonConvert.SerializeObject(new
   {
      abc = "jsjs",
      xyz = "hhhh"
    }));
data.Headers.ContentType = new MediaTypeHeaderValue("application/json"); // <--
var response = await client.PostAsync(url, data);

上面的代码在vbnet:

dim FeToSend as new (object--> define class)

Dim client As New HttpClient
Dim content = New StringContent(FeToSend.ToString(), Encoding.UTF8,"application/json")
content.Headers.ContentType = New MediaTypeHeaderValue( "application/json" )
Dim risp = client.PostAsync(Chiamata, content).Result

msgbox(risp.tostring)

希望这对你有所帮助

当我做这份工作时，我想用一个回答来回答所有问题，作为对所有人和我自己的提醒:

根据Serez的回答，HttpContent派生类列表如下 https://stackoverflow.com/a/42380027/914284

HttpClient PostAsync有一些背景，这取决于你正在工作的上下文!

在情况下，您可以根据希望发送到服务器的类型发布数据 服务器上下文等待它，如下所示

[HttpPost] 公共异步特别工作组< iasult > Submit(我的模型) [HttpPost] 公共异物特别工作组< iasult > Submit([FromForm]我的模型) [HttpPost] 公共异物特别工作组< iasult > Submit([身体]我的模型)

当写入FromForm或Body时，它的工作方式是FromForm。 FromBody需要json内容，否则它需要KeyValuePairs作为行。它们都有一些实现，如下:

对于FromForm:我已经使用了一个扩展

public static class HelperExtensions
    {
        public static FormUrlEncodedContent ToFormData(this object obj)
        {
            var formData = obj.ToKeyValue();

            return new FormUrlEncodedContent(formData);
        }

        public static IDictionary<string, string> ToKeyValue(this object metaToken)
        {
            if (metaToken == null)
            {
                return null;
            }

            // Added by me: avoid cyclic references
            var serializer = new JsonSerializer { ReferenceLoopHandling = ReferenceLoopHandling.Ignore };
            if (metaToken is not JToken token)
            {
                // Modified by me: use serializer defined above
                return ToKeyValue(JObject.FromObject(metaToken, serializer));
            }

            if (token.HasValues)
            {
                var contentData = new Dictionary<string, string>();
                foreach (var child in token.Children().ToList())
                {
                    var childContent = child.ToKeyValue();
                    if (childContent != null)
                    {
                        contentData = contentData.Concat(childContent)
                                                 .ToDictionary(k => k.Key, v => v.Value);
                    }
                }

                return contentData;
            }

            var jValue = token as JValue;
            if (jValue?.Value == null)
            {
                return null;
            }

            var value = jValue?.Type == JTokenType.Date ?
                            jValue?.ToString("o", CultureInfo.InvariantCulture) :
                            jValue?.ToString(CultureInfo.InvariantCulture);

            return new Dictionary<string, string> { { token.Path, value } };
        }
    }

对于FromBody:使用任何json转换库Newtonsoft或microsoft

using Newtonsoft.Json;

var jsonString = JsonConvert.SerializeObject(obj);

在这两种类型中，内容类型都应该根据需求来定义，例如json(写入头)

request.Headers.Accept.Clear();
request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

或者另一种用法

        using (var content = new StringContent(JsonConvert.SerializeObject(answer), System.Text.Encoding.UTF8, "application/json"))
        {
            var answerResponse = await client.PostAsync(url, content);
            //use await it has moved in some context on .core 6.0
        }

如果你应该在上下文上使用授权，你也可以提供如下授权:

httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", "Your Oauth token");