HttpPost from PostAsync always null

Question

I'm about to go nuts trying to figure out how to pass POST parameters to Web API methods in ASPNET CORE 2.0.

I have a C# client application and a C# server application.

• I've tried using [FromBody] on the Web Api method.
• I've tried setting the content type to "application/json"
• I've simplified my controller action to be as basic as possible
• I have tried passing both a string and a complex object.

It's ALWAYS NULL. What is going on?

Client code:

private static async Task SendCustomObject()
{
    var controllerName = "BasicApi";
    var basicClientApi = string.Format("http://localhost:5100/api/{0}", controllerName);

    using (var httpClient = new HttpClient()){

        var packetData = new TestPacket();
        var jsonObj = new { json = packetData };
        JObject jobject = JObject.FromObject(packetData);

        var json = JsonConvert.SerializeObject(jobject);
        var content = new StringContent(json, Encoding.UTF8, "application/json");
        content.Headers.ContentType = new MediaTypeHeaderValue("application/json");

        // This doesn't help:
        //httpClient.DefaultRequestHeaders.Accept.Clear();
        //httpClient.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));

        var response = await httpClient.PostAsync(basicClientApi, content);                    

        if (!response.IsSuccessStatusCode)
        {
            Console.WriteLine(response.StatusCode);
        }
        else
        {
            var rawResponse = await response.Content.ReadAsStringAsync();                        

            JObject o = JObject.Parse(rawResponse);
            Console.WriteLine(o.ToString());    
        }
    }
}

Server code:

namespace myApp.Controllers
{
    [Route("api/[controller]")]
    public class BasicApiController : Controller
    {    

      [HttpPost]    
      public JsonResult Post([FromBody] string json) // json is always null!
      {                

        var jsonData = JsonConvert.DeserializeObject<Models.TestPacket>(json);
        return Json(new { result = true });

      }
    }
 }

Answer 1

ASP.NET Core default binder de-serializes the models for you, you don't need to do it by hand. Specifically, you cannot treat an object as if it was a string.

Look at this much simpler example:

private static async Task SendCustomObject()
{
    var controllerName = "BasicApi";
    var basicClientApi = string.Format("http://localhost:5100/api/{0}", controllerName);

    using (var httpClient = new HttpClient()){

        var packetData = new TestPacket();
        var jsonObj = new { json = packetData };

        var json = JsonConvert.SerializeObject(jsonObj); // no need to call `JObject.FromObject`
        var content = new StringContent(json, Encoding.UTF8, "application/json");
        content.Headers.ContentType = new MediaTypeHeaderValue("application/json");

        var response = await httpClient.PostAsync(basicClientApi, content);                    

        if (!response.IsSuccessStatusCode)
        {
            Console.WriteLine(response.StatusCode);
        }
        else
        {
            var rawResponse = await response.Content.ReadAsStringAsync();                        

            JObject o = JObject.Parse(rawResponse);
            Console.WriteLine(o.ToString());    
        }
    }
}

namespace myApp.Controllers
{
    [Route("api/[controller]")]
    public class BasicApiController : Controller
    {    

      [HttpPost]    
      // don't ask for a string, ask for the model you are expecting to recieve
      public JsonResult Post(Models.TestPacket json)
      {                
           return Json(new { result = true });
      }
    }
 }