You should use the SendAsync method instead, this is a generic method, that serializes the input to the service
Widget widget = new Widget()
widget.Name = "test"
widget.Price = 1;
HttpClient client = new HttpClient();
client.BaseAddress = new Uri("http://localhost:44268/api/test");
client.SendAsync(new HttpRequestMessage<Widget>(widget))
.ContinueWith((postTask) => postTask.Result.EnsureSuccessStatusCode() );
If you don't want to create the concrete class, you can make it with the FormUrlEncodedContent class
var client = new HttpClient();
// This is the postdata
var postData = new List<KeyValuePair<string, string>>();
postData.Add(new KeyValuePair<string, string>("Name", "test"));
postData.Add(new KeyValuePair<string, string>("Price ", "100"));
HttpContent content = new FormUrlEncodedContent(postData);
client.PostAsync("http://localhost:44268/api/test", content).ContinueWith(
(postTask) =>
{
postTask.Result.EnsureSuccessStatusCode();
});
Note: you need to make your id to a nullable int (int?)