Can't get error message on BadRequest in Web Api 2

Question

I've googled a lot searching for an answer to my problem with no luck so, let's try if someone else can help me.

I have a Web Api 2 action to register an user after doing some validations. If everything works, it return the serialized user and if don't, an error message sent within a BadRequest response.

At the other hand, I have a WPF client that calls the API for a response.

My problem is that I can't get the reason sent by the error, the client just get the Bad Request error message.

This is a part of the code:

• Web Api Action:

  public async Task<IHttpActionResult> AddUser(NewUserDTO {
      if (!ModelState.IsValid)
      {
          return BadRequest(ModelState);
      }
      if (!model.IdCliente.HasValue)
      {
          ModelState.AddModelError("", "No existe el cliente");
          return BadRequest(ModelState);
      }
      // do save stuff
      return Ok(TheModelFactory.Create(user));
  }
  

• Client function:

  public async Task<ApplicationUserDTO> AddUser(NewUserDTO dto) {
      using (var client = new HttpClient()) {
          client.BaseAddress = new Uri(_urlBase);
          client.DefaultRequestHeaders.Accept.Clear();
          client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
          client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", Token);
          HttpContent content = new StringContent(JsonConvert.SerializeObject(dto));
          content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
          HttpResponseMessage responseMessage = await client.PostAsync("api/accounts/AddUser", content);
          if (responseMessage.IsSuccessStatusCode) {
              var responseJson = await responseMessage.Content.ReadAsStringAsync();
              user = JsonConvert.DeserializeObject<ApplicationUserDTO>(responseJson);
          }
          else
               MessageBox.Show(responseMessage.Content.ReadAsStringAsync().Result);
          return user;
      } 
  }
  

Anyone can help?

Edited:

• DTO:

  [Serializable]
  public class NewUserDTO {
  public int? IdCliente { get; set; }
  [Required]
  public string UserName { get; set; }
  [Required]
  public string Email { get; set; }
  public string Role { get; set; }
  public string Password { get; set; } }
  

Anyway... the dto is sent correctly to api nut, here's the serialized dto as you asked for:

"{\"IdCliente\":null,\"UserName\":\"Toni\",\"Email\":\"[email protected]\",\"Role\":\"Filtra\",\"Password\":\"TONI\"}"

Answer 1

API

return new BadRequestErrorMessageResult(yourErrorMessage);

Client

var errorMessage = responseMessage.Content.ReadAsStringAsync().GetAwaiter().GetResult();
MessageBox.Show(errorMessage);