InvalidCastException 'HttpResponseMessage' to 'IHttpActionResult' on WebApi2 GET - asp.net

Question

Recently I've been following some WebApi2 tutorials. I have a situation whereby if a requested GET operation returns data outside of the user's remit, then I need to return a Forbidden code.
Imports System.Net
Imports System.Net.Http
Imports System.Web.Http
Namespace Controllers
Public Class MyController
Inherits ApiController
<Route("Records/{id}")>
Public Function [Get](id As Int32) As IHttpActionResult
If Not Remit.IsWithinRemit(id) Then
Return Request.CreateErrorResponse(HttpStatusCode.Forbidden, "This data is not within your remit")
Else
Dim r As New CustomObject(id)
Return Ok(r)
End If
End Function
End Class
End Namespace
Unfortunately, although the Ok(r) part works okay, CreateErrorResponse throws an InvalidCastException:
Unable to cast object of type 'System.Net.Http.HttpResponseMessage' to type 'System.Web.Http.IHttpActionResult'.
I know why the error is happening, but am unsure of the correct approach of how to fix it.
In other threads, people advise that CreateErrorResponse() is the best approach for WebApi2, but VS creates it's sample GET request returning IHttpActionResult. Its like stuff doesn't seem to fit together for us newbies at the moment...

Answer 1

No, it isn't obvious, but you can get what you want (error code plus message) AND return it from a method of type IHttpActionResult. No need to change the return type or go without error messages.
This is the helper class:
public class ErrorResult : IHttpActionResult
{
private HttpRequestMessage Request { get; }
private HttpStatusCode statusCode;
private string message;
public ErrorResult(HttpRequestMessage request, HttpStatusCode statusCode, string message)
{
this.Request = request;
this.statusCode = statusCode;
this.message = message;
}
public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
{
return Task.FromResult(Request.CreateErrorResponse(statusCode, message));
}
}
and you can call it like this:
public IHttpActionResult MyMethod()
{
MyServiceLayer myServiceLayer = new MyServiceLayer();
MyType myvar;
if (MyServiceLayer.EverythingIsOK(ref myvar))
return Ok(myvar);
else
return new ErrorResult(Request, HttpStatusCode.SomeErrorCode, "Something Is Wrong");
}

Answer 2

try this
Change your Get method to return "HttpResponseMessage"
<Route("Records/{id}")>
Public Function [Get](id As Int32) As HttpResponseMessage
If Not Remit.IsWithinRemit(id) Then
Return Request.CreateResponse(HttpStatusCode.Forbidden, "This data is not within your remit")
Else
Dim r As New CustomObject(id)
Return Request.CreateResponse(HttpStatusCode.OK, r)
End If
End Function
Check below link
http://www.asp.net/web-api/overview/web-api-routing-and-actions/action-results

Answer 3

I found an alternative possible solution (there may be better but this one works and is simple). It returns
403 Forbidden
but with no content:
<Route("Records/{id}")>
Public Function [Get](id As Int32) As IHttpActionResult
If Not Remit.IsWithinRemit(id) Then
Return New Results.StatusCodeResult(HttpStatusCode.Forbidden, Request)
Else
Dim r As New CustomObject(id)
Return Ok(r)
End If
End Function
Because HttpResponseMessage comes from the same namespace, and also allows you to return custom error messages in addition to a HTTP status code, that option is more suitable to use in most cases.
I guess IHttpActionResult is for basic status code returns with no frills. I posted this alongside the above answer to give new coders visibility of both options.

Answer 4

I encountered the same error using .NET Framework 4.7.2. Rather than changing the return type** from IHttpActionResult, I corrected the bug by wrapping myHttpResponseMessage object in a ResponseMessageResult like this: -
return new ResponseMessageResult(myHttpResponseMessage);
** it was a single, custom case amongst a set of straightforward IHttpActionResult cases in a switch block