Is it possible to intercept an action from becoming a ContentResult?

Question

I am attempting to write a filter that wraps data to follow the JSON API spec and so far I've got it working on all cases where I directly return an ActionResult, such as ComplexTypeJSON. I am trying to get it to work in situations like ComplexType where I do not have to run the Json function constantly.

[JSONAPIFilter]
public IEnumerable<string> ComplexType()
{
    return new List<string>() { "hello", "world" };
}

[JSONAPIFilter]
public JsonResult ComplexTypeJSON()
{
    return Json(new List<string>() { "hello", "world" });
}

However, by the time public override void OnActionExecuted(ActionExecutedContext filterContext) runs when I navigate to ComplexType, the filterContext.Result is a Content Result, that is just a string where filterContext.Result.Content is simply:

"System.Collections.Generic.List`1[System.String]"

Is there a way I can set something up to make ComplexType become JsonResult rather than ContentResult?

For context, here are the exact files:

TestController.cs

namespace MyProject.Controllers
{
    using System;
    using System.Collections.Generic;
    using System.Web.Mvc;

    using MyProject.Filters;

    public class TestController : Controller
    {
        [JSONAPIFilter]
        public IEnumerable<string> ComplexType()
        {
            return new List<string>() { "hello", "world" };
        }

        [JSONAPIFilter]
        public JsonResult ComplexTypeJSON()
        {
            return Json(new List<string>() { "hello", "world" });
        }

        // GET: Test
        [JSONAPIFilter]
        public ActionResult Index()
        {
            return Json(new { foo = "bar", bizz = "buzz" });
        }

        [JSONAPIFilter]
        public string SimpleType()
        {
            return "foo";
        }

        [JSONAPIFilter]
        public ActionResult Throw()
        {
            throw new InvalidOperationException("Some issue");
        }
    }
}

JSONApiFilter.cs

namespace MyProject.Filters
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web.Mvc;

    using MyProject.Exceptions;
    using MyProject.Models.JSONAPI;

    public class JSONAPIFilterAttribute : ActionFilterAttribute, IExceptionFilter
    {
        private static readonly ISet<Type> IgnoredTypes = new HashSet<Type>()
                                                              {
                                                                  typeof(FileResult),
                                                                  typeof(JavaScriptResult),
                                                                  typeof(HttpStatusCodeResult),
                                                                  typeof(EmptyResult),
                                                                  typeof(RedirectResult),
                                                                  typeof(ViewResultBase),
                                                                  typeof(RedirectToRouteResult)
                                                              };

        private static readonly Type JsonErrorType = typeof(ErrorModel);

        private static readonly Type JsonModelType = typeof(ResultModel);

        public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            if (filterContext == null)
            {
                throw new ArgumentNullException("filterContext");
            }

            if (IgnoredTypes.Any(x => x.IsInstanceOfType(filterContext.Result)))
            {
                base.OnActionExecuted(filterContext);
                return;
            }

            var resultModel = ComposeResultModel(filterContext.Result);
            var newJsonResult = new JsonResult()
                                    {
                                        JsonRequestBehavior = JsonRequestBehavior.AllowGet,
                                        Data = resultModel
                                    };

            filterContext.Result = newJsonResult;
            base.OnActionExecuted(filterContext);
        }

        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            var modelState = filterContext.Controller.ViewData.ModelState;

            if (modelState == null || modelState.IsValid)
            {
                base.OnActionExecuting(filterContext);
            }
            else
            {
                throw new ModelStateException("Errors in ModelState");
            }
        }

        public virtual void OnException(ExceptionContext filterContext)
        {
            if (filterContext == null)
            {
                throw new ArgumentNullException("filterContext");
            }

            if (filterContext.Exception == null) return;

            // Todo: if modelstate error, do not provide that message
            // set status code to 404

            var errors = new List<string>();

            if (!(filterContext.Exception is ModelStateException))
            {
                errors.Add(filterContext.Exception.Message);
            }

            var modelState = filterContext.Controller.ViewData.ModelState;
            var modelStateErrors = modelState.Values.SelectMany(x => x.Errors).Select(x => x.ErrorMessage).ToList();
            if (modelStateErrors.Any()) errors.AddRange(modelStateErrors);

            var errorCode = (int)System.Net.HttpStatusCode.InternalServerError;
            var errorModel = new ErrorModel()
                                 {
                                     status = errorCode.ToString(),
                                     detail = filterContext.Exception.StackTrace,
                                     errors = errors,
                                     id = Guid.NewGuid(),
                                     title = filterContext.Exception.GetType().ToString()
                                 };
            filterContext.ExceptionHandled = true;
            filterContext.HttpContext.Response.Clear();
            filterContext.HttpContext.Response.TrySkipIisCustomErrors = true;
            filterContext.HttpContext.Response.StatusCode = errorCode;

            var newResult = new JsonResult() { Data = errorModel, JsonRequestBehavior = JsonRequestBehavior.AllowGet };

            filterContext.Result = newResult;
        }

        private ResultModel ComposeResultModel(ActionResult actionResult)
        {
            var newModelData = new ResultModel() { };

            var asContentResult = actionResult as ContentResult;
            if (asContentResult != null)
            {
                newModelData.data = asContentResult.Content;
                return newModelData;
            }

            var asJsonResult = actionResult as JsonResult;
            if (asJsonResult == null) return newModelData;

            var dataType = asJsonResult.Data.GetType();
            if (dataType != JsonModelType)
            {
                newModelData.data = asJsonResult.Data;
            }
            else
            {
                newModelData = asJsonResult.Data as ResultModel;
            }

            return newModelData;
        }
    }
}

Answer 1

There are two options:

1.use ApiController instead of Controller

The apicontroller will return json result,and the default serializer is Newtonsoft.json(here),so you can use like this below:

//the response type
public class SimpleRes
{
    [JsonProperty(PropertyName = "result")]
    public string Result;      
}

//the controller
 public class TestController : ApiController
 {  
    [HttpGet] 
    [HttpPost]
    [JSONAPIFilter]
    public SimpleRes TestAction()
    {
        return new SimpleRes(){Result = "hello world!"};
    }
 }

2.wrap your response with your own ActionResult if you insist using Controller:

//json container
public class AjaxMessageContainer<T>
{        
    [JsonProperty(PropertyName = "result")]
    public T Result { set; get; }
}

//your own actionresult
public class AjaxResult<T> : ActionResult
{        
    private readonly T _result;                      

    public AjaxResult(T result)
    {          
        _result = result;           
    }

    public override void ExecuteResult(ControllerContext context)
    {
        context.HttpContext.Response.Clear();
        context.HttpContext.Response.ContentType = "application/json";
        var result = JsonConvert.SerializeObject(new AjaxMessageContainer<T>
        {               
            Result = _result,               
        });
        var bytes =
            new UTF8Encoding().GetBytes(result);
        context.HttpContext.Response.OutputStream.Write(bytes, 0, bytes.Length);           
    }
}

//your controller
[JSONAPIFilter]
public AjaxResult<List<String>> TestSimple()
{
    return AjaxResult<List<String>>(new List<string>() { "hello", "world" });
}

and if you wanna get response string from filter for log or something:

var result  = filterContext.Response.Content.ReadAsStringAsync();

Answer 2

I think this is what you are looking for :

public class JSONAPIFilterAttribute : ActionFilterAttribute, IActionFilter
{
    void IActionFilter.OnActionExecuted(ActionExecutedContext context)
    {
        context.Result = new JsonResult
        {
            Data = ((ViewResult)context.Result).ViewData.Model
        };
    }
}

From @roosteronacid : return jsonresult in actionfilter