使用WebClient。UploadString或WebClient。UploadData可以轻松地将数据POST到服务器。我将展示一个使用UploadData的示例，因为UploadString的使用方式与DownloadString相同。

byte[] bret = client.UploadData("http://www.website.com/post.php", "POST",
                System.Text.Encoding.ASCII.GetBytes("field1=value1&field2=value2") );
 
string sret = System.Text.Encoding.ASCII.GetString(bret);

更多:http://www.daveamenta.com/2008-05/c-webclient-usage/

大多数答案都是旧的。只是想分享一下对我有用的方法。为了实现异步操作，例如在。net 6.0 Preview 7中使用WebClient异步发布数据到特定的URL， . net Core和其他版本都可以使用WebClient。UploadStringTaskAsync方法。

使用命名空间System.Net;对于ResponseType类来捕获来自服务器的响应，我们可以使用这个方法将数据POST到特定的URL。请确保在调用此方法时使用await关键字

    public async Task<ResponseType> MyAsyncServiceCall()
    {
        try
        {
            var uri = new Uri("http://your_uri");
            var body= "param1=value1&param2=value2&param3=value3";

            using (var wc = new WebClient())
            {
                wc.Headers[HttpRequestHeader.Authorization] = "yourKey"; // Can be Bearer token, API Key etc.....
                wc.Headers[HttpRequestHeader.ContentType] = "application/json"; // Is about the payload/content of the current request or response. Do not use it if the request doesn't have a payload/ body.
                wc.Headers[HttpRequestHeader.Accept] = "application/json"; // Tells the server the kind of response the client will accept.
                wc.Headers[HttpRequestHeader.UserAgent] = "PostmanRuntime/7.28.3"; 
                
                string result = await wc.UploadStringTaskAsync(uri, body);
                return JsonConvert.DeserializeObject<ResponseType>(result);
            }
        }
        catch (Exception e)
        {
            throw new Exception(e.Message);
        }
    }

有一个内置的方法叫做UploadValues，它可以发送HTTP POST(或任何类型的HTTP方法)，并以适当的数据格式处理请求体的构造(用“&”连接参数并通过url编码转义字符):

using(WebClient client = new WebClient())
{
    var reqparm = new System.Collections.Specialized.NameValueCollection();
    reqparm.Add("param1", "<any> kinds & of = ? strings");
    reqparm.Add("param2", "escaping is already handled");
    byte[] responsebytes = client.UploadValues("http://localhost", "POST", reqparm);
    string responsebody = Encoding.UTF8.GetString(responsebytes);
}

使用简单客户端。UploadString(地址、内容);正常工作很好，但我认为应该记住，如果没有返回HTTP成功状态码，将抛出webeexception。我通常这样处理，打印远程服务器返回的任何异常消息:

try
{
    postResult = client.UploadString(address, content);
}
catch (WebException ex)
{
    String responseFromServer = ex.Message.ToString() + " ";
    if (ex.Response != null)
    {
        using (WebResponse response = ex.Response)
        {
            Stream dataRs = response.GetResponseStream();
            using (StreamReader reader = new StreamReader(dataRs))
            {
                responseFromServer += reader.ReadToEnd();
                _log.Error("Server Response: " + responseFromServer);
            }
        }
    }
    throw;
}

下面是简单明了的答案:

public String sendSMS(String phone, String token) {
    WebClient webClient = WebClient.create(smsServiceUrl);

    SMSRequest smsRequest = new SMSRequest();
    smsRequest.setMessage(token);
    smsRequest.setPhoneNo(phone);
    smsRequest.setTokenId(smsServiceTokenId);

    Mono<String> response = webClient.post()
          .uri(smsServiceEndpoint)
          .header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
          .body(Mono.just(smsRequest), SMSRequest.class)
          .retrieve().bodyToMono(String.class);

    String deliveryResponse = response.block();
    if (deliveryResponse.equalsIgnoreCase("success")) {
      return deliveryResponse;
    }
    return null;
}

//Making a POST request using WebClient.
Function()
{    
  WebClient wc = new WebClient();

  var URI = new Uri("http://your_uri_goes_here");

  //If any encoding is needed.
  wc.Headers["Content-Type"] = "application/x-www-form-urlencoded";
  //Or any other encoding type.

  //If any key needed

  wc.Headers["KEY"] = "Your_Key_Goes_Here";

  wc.UploadStringCompleted += 
      new UploadStringCompletedEventHandler(wc_UploadStringCompleted);

  wc.UploadStringAsync(URI,"POST","Data_To_Be_sent");    
}

void wc__UploadStringCompleted(object sender, UploadStringCompletedEventArgs e)    
{  
  try            
  {          
     MessageBox.Show(e.Result); 
     //e.result fetches you the response against your POST request.         
  }
  catch(Exception exc)         
  {             
     MessageBox.Show(exc.ToString());            
  }
}