InvalidCastException 'HttpResponseMessage' to 'IHttpActionResult' on WebApi2 GET

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