new HttpClient().PostAsync封装参数

var data = Encoding.UTF8.GetBytes("{ \"y\": 5, \"x\": 3}");
var content = new ByteArrayContent(data);
content.Headers.ContentType = MediaTypeHeaderValue.Parse("application/json");
var response = new HttpClient().PostAsync(_AddUrl, content).Result;
var responseContent = response.Content.ReadAsStringAsync().Result;