C# .net Core catch custom Exception

Question

Where is my fault?

I have a class type Exception

public class ApiException : Exception {
  public ApiException(string message) : base(message) {
  }
}

In some situations I call throw new ApiException("Message"); For example here:

public static async Task<string> ValidateToken(string token) {
  Dictionary<string, string> values = new Dictionary<string, string> {
    { "token", token}
  };

  FormUrlEncodedContent content = new FormUrlEncodedContent(values);
  HttpResponseMessage response = await client.PostAsync(Globals.sso, content);

  string responseString = await response.Content.ReadAsStringAsync();

  if (response.IsSuccessStatusCode) {
    TokenResp result = JsonConvert.DeserializeObject<TokenResp>(responseString);
    if (result.Token != token)
      throw new ApiException("Token is invalid");
  } else {
    NonFieldResponse resp = JsonConvert.DeserializeObject<NonFieldResponse>(responseString);
    string msg = null;

    foreach (string message in resp.non_field_errors) {
      if (msg != null) msg += ", ";
      msg += message;
    }

    throw new ApiException(msg);
  }

In somewhere I need to catch exceptions like here:

try {
  Type = ValidateToken(token).Result;
} catch (ApiException ae) {
  Console.WriteLine(ae.Message);
} catch (Exception e) {
  Console.WriteLine(e.Message);
}

But catch (ApiException ae) doesn't happens, always catched simple Exception (where e.GetType() is AggregateException and e.InnerException.GetType() is ApiException ).

How to catch my exception?

Answer 1

-- edit, after seeing code that is even more real:

• When your caller is not async, be careful because this can cause deadlocks:

// Type = ValidateToken(token).Result;
   Type = ValidateToken(token).GetAwaiter().GetResult();

• when you caller method is also async:

Type = await ValidateToken(token); 

Both of these will 'unwrap' the aggregate exception.
Your custom exception is of course one of the InnerExceptions of that AggregateException.

Answer 2

You ApiException will not get caught properly unless you await the ValidateToken() call. When you use:

Type = ValidateToken(token)Result;

instead of:

Type = await ValidateToken(token);

Your exceptions will be wrapped in an AggregateException .

Using await properly will allow the proper exception to get caught.

Use this:

try {
  Type = await ValidateToken(token);
} catch (ApiException ae) {
  Console.WriteLine(ae.Message);
}