Next up in our ASP.NET Core Demystified series, we will discuss and demo a whole bunch of classes which implement the IActionResult interface and inherit from the corresponding ActionResult class. These classes are used as responses from controller actions, and include redirecting to another site, redirecting to a different controller action, returning a JSON object, and returning a file to the browser.

In this post, we will first discuss the IActionResult interface and what it needs, and then we will see demos for many of the available implementations of that interface and scenarios in which we might use each of them.

As always with my tutorial posts, there's a working project over on GitHub that demonstrates the Action Results we'll be discussing in this post. Check it out!

What are Action Results?

In the strictest sense, Action Results are any class which implements the IActionResult interface from ASP.NET Core MVC. However, all the action results we will see in this post will also inherit from the ActionResult class.

In short, Action Results are classes which represent things the client is supposed to do as a result of the controller action. They may need to get a file, or redirect, or any of a myriad things. Some Action Results merely return an HTTP status code. In short, the most common things the client might want to do after calling a controller action are represented as Action Results.

Content Negotiation

Content Negotiation (conneg for short) occurs when the request has an Accept header. It is the process by which the server determines the format in which to send the response. By default, ASP.NET Core uses JSON for responses, but the request Accept header can specify other formats (such as XML) and the server will attempt to return the response in the specified format.

A team of students hold a negotation.

Image is Warsaw Negotiation Round Senate of Poland 2014 01, found on Wikimedia and used under license

When the server detects an Accept header in the request, it will enumerate the media types in that header in an effort to find one that the server supports. If no media type is found that the server can support, the server will use the first of its supported media types that can create the request (hence why this process is called content negotiation and not give me this format now dammit).

Action Result Sets

There are five major sets of Action Results:

  • Status Code Results
  • Status Code w/ Object Results
  • Redirect Results
  • File Results
  • Content Results

We will discuss each of these sets individually, and show examples for the kinds of results in them. All the demos you will see in this post are also in the sample project on GitHub, so check that out too!

Status Code Results

Arguably the simplest kind of action result that is defined by ASP.NET Core MVC is the collection of Status Code Results. These results merely return an HTTP status code to the client.

OkResult

The OkResult (short method: Ok()) return the 200 OK status code.

public IActionResult OkResult()
{
    return Ok();
}

CreatedResult

The CreatedResult (short method: Created()) returns 201 Created with a URL to the created resource.

public IActionResult CreatedResult()
{
    return Created("http://example.org/myitem", new { name = "testitem" });
}

NoContentResult

The NoContentResult (short method: NoContent()) returns a 204 No Content status code, indicating that the server successfully processed the request, but that there is nothing to return.

public IActionResult NoContentResult()
{
    return NoContent();
}

BadRequestResult

The BadRequestResult (short method: BadRequest()) return 400 Bad Request, which indicates that the server cannot process the request due to an error in said request. This is often used in APIs when validation of the request fails (and there isn't a more specific code that would fit better).

public IActionResult BadRequestResult()
{
    return BadRequest();
}

UnauthorizedResult

The UnauthorizedResult (short method: Unauthorized()) returns 401 Unauthorized, indicating that the request cannot be processed because the user making the request doesn't have the appropriate authentication to do so (meaning this status code should really have been called 401 Unauthenticated).

public IActionResult UnauthorizedResult()
{
    return Unauthorized();
}

NotFoundResult

The NotFoundResult (short method: NotFound()) returns the 404 Not Found status code, indicating that the requested resource, for whatever reason, was not found on the server.

public IActionResult NotFoundResult()
{
    return NotFound();
}

UnsupportedMediaTypeResult

The UnsupportedMediaTypeResult, which doesn't have a short method at the time of writing, returns 415 Unsupported Media Type, indicating that the media type (e.g. the Content-Type header on the request) is not supported by this server. For example, a server might return this status code if the user attempts to upload an image in the .bmp format, but the server only accepts .jpeg.

public IActionResult UnsupportedMediaTypeResult()
{
    return new UnsupportedMediaTypeResult();
}

Other Status Codes

The above status code results do not cover all the possible HTTP status codes (of which there are many). For situations in which you need to return a status code which isn't given a dedicated action result, we can use the generic StatusCodeResult (short method: StatusCode()).

public IActionResult StatusCodeResult(int statusCode)
{
    return StatusCode(statusCode);
}

Status Code with Object Results

These action results are, for the most part, overloads of the results seen in the previous section. However, they are handled differently by the browser or other requesters due to content negotiation.

OkObjectResult

The OkObjectResult returns 200 OK as well as an object.

public IActionResult OkObjectResult()
{
    var result = new OkObjectResult(new { message = "200 OK", currentDate = DateTime.Now });
    return result;
}

CreateObjectResult

The CreatedObjectResult returns 201 Created and a custom object.

public IActionResult CreatedObjectResult()
{
    var result = new CreatedAtActionResult("createdobjectresult", "statuscodeobjects", "", new { message = "201 Created", currentDate = DateTime.Now });
    return result;
}

BadRequestObjectResult

The BadRequestObjectResult does exactly what you think it does; it returns 400 Bad Request and an object.

public IActionResult BadRequestObjectResult()
{
    var result = new BadRequestObjectResult(new { message = "400 Bad Request", currentDate = DateTime.Now });
    return result;
}

NotFoundObjectRequest

I imagine by now you're seeing the pattern? The NotFoundObjectRequest returns 404 Not Found and an object.

public IActionResult NotFoundObjectResult()
{
    var result = new NotFoundObjectResult(new { message = "404 Not Found", currentDate = DateTime.Now });
    return result;
}

ObjectResult

For scenarios which aren't covered by the above types, we have the ObjectResult class. It returns the specified status code and an object.

public IActionResult ObjectResult(int statusCode)
{
    var result = new ObjectResult(new { statusCode = statusCode, currentDate = DateTime.Now });
    result.StatusCode = statusCode;
    return result;
}

Redirect Results

Sometimes we will need to tell the client (e.g. the browser) to redirect to another location. That's where the redirect results come in: they tell the client where to redirect to. Sometimes we just need to go to another action in the same project, but other times we will need to redirect to an external resource.

RedirectResult

The basic RedirectResult class (short method: Redirect()) redirects to a specified URL.

public IActionResult RedirectResult()
{
    return Redirect("https://www.exceptionnotfound.net");
}

LocalRedirectResult

The LocalRedirectResult (short method: LocalRedirect()) redirects to a URL within the same application. For example, if your site is http://www.mysite.com and you want to redirect to the URL http://www.mysite.com/redirects/target (e.g. the "target" action in the "redirects" controller), you could do so like this:

public IActionResult LocalRedirectResult()
{
    return LocalRedirect("/redirects/target");
}

RedirectToActionResult

The very common RedirectToActionResult class (short method: RedirectToAction()) redirects the client to a particular action and controller within the same application. If you wanted to do the same redirect as in the LocalRedirectResult example, you would do the following:

public IActionResult RedirectToActionResult()
{
    return RedirectToAction("target");
}

RedirectToRouteResult

ASP.NET Core MVC has the concept of Routing, by which we can create URL templates which map to specific controllers and actions. Correspondingly, we also have the result RedirectToRouteResult (short method: RedirectToRoute()) which redirects to a specific route already defined in the application.

Let's say we have the following route defined in our Startup.cs class:

app.UseMvc(routes =>
{
    routes.MapRoute(
        name: "default",
        template: "{controller=Home}/{action=Index}/{id?}");
});

We could redirect using that specific route and the RedirectToRoute() short method and end up at the same Target action as the previous two examples:

public IActionResult RedirectToRouteResult()
{
    return RedirectToRoute("default", new { action = "target", controller = "redirects" });
}

File Results

If we need to return a file to the requester, the File Results let us do so using a variety of formats.

In this demo, we have a file called pdf-sample.pdf in the wwwroot/downloads folder, and we will use that file to demonstrate how various File Result classes work.

FileResult

The basic FileResult class (short method: File()) returns a file at a given path. In our case, the path is /wwwroot/downloads, and so our action will look as follows:

public IActionResult FileResult()
{
    return File("~/downloads/pdf-sample.pdf", "application/pdf");
}

Note that "application/pdf" is the MIME type associated with this file.

FileContentResult

There may come a time when we only want to return the content of a given file as a byte array (byte[]), not the entire file. For this scenario, we can use the FileContentResult class. Note that we still need to specify a MIME type:

public IActionResult FileContentResult()
{
    //Get the byte array for the document
    var pdfBytes = System.IO.File.ReadAllBytes("wwwroot/downloads/pdf-sample.pdf");

    //FileContentResult needs a byte array and returns a file with the specified content type.
    return new FileContentResult(pdfBytes, "application/pdf");
}

VirtualFileResult

We can also use the VirtualFileResult class to get files out of the /wwwroot folder in our project, like so:

public IActionResult VirtualFileResult()
{
    //Paths given to the VirtualFileResult are relative to the wwwroot folder.
    return new VirtualFileResult("/downloads/pdf-sample.pdf", "application/pdf");
}

PhysicalFileResult

Finally, if we need to get a file from a physical path on our server that isn't necessarily part of our project, we can use the PhysicalFileResult class:

public IActionResult PhysicalFileResult()
{
    return new PhysicalFileResult(_hostingEnvironment.ContentRootPath + "/wwwroot/downloads/pdf-sample.pdf", "application/pdf");
}

Note that _hostingEnvironment.ContentRootPath is the path to the application root, not the /wwwroot folder.

Content Results

The final set of Result classes are the Content Result classes, which are designed to return various kinds of content to the controller.

ViewResult

Possibly the most basic Result class in all of ASP.NET Core MVC is the ViewResult class (short method: View()), which returns a view.

public IActionResult Index()
{
    return View();
}

Note that, by default, the View() method returns a view with the same name as the action it is called from, in a folder with the same name as the controller. In our case, the controller is "Content" and the action is "Index" so ASP.NET Core MVC will look for a file at /Views/Content/Index.cshtml. You can specify that other views get returned by using overloads of the View() short method.

PartialViewResult

It is also possible to return a partial view from an action using the PartialViewResult class (short method: PartialView()), like so:

public IActionResult PartialViewResult()
{
    return PartialView();
}

In our demo, the code above will look for a view named "PartialViewResult" in both the /Views/Content directory and the /Views/Shared directory, and will find it in /Views/Shared.

JsonResult

You can easily return JavaScript Object Notation (JSON) content from your application by using the JsonResult class (short method: Json()).

public IActionResult JsonResult()
{
    return Json(new { message = "This is a JSON result.", date = DateTime.Now });
}

ContentResult

If you need to return content which doesn't fall into one of the above categories, you can use the general ContentResult object (short method: Content()) to return your content. In our demo, we will return a simple message, but you can use this class to return more complex content by specifying the MediaTypeHeaderValue or the content type.

public IActionResult ContentResult()
{
    return Content("Here's the ContentResult message.");
}

Summary

The Action Result classes in ASP.NET Core MVC provide a significant chunk of the functionality you'll be using in your controllers. They return status codes, objects, files, other content, and even redirect the client. As you get more familiar with ASP.NET Core MVC and its functionality, these classes will become second nature; until then, use this post as a quick reference to get your code written.

As always with my tutorials, there's a working code sample over on GitHub that can you use to familiarize yourself with all the Action Result available in ASP.NET Core MVC.

Let me know what you thought of this post and the demo project in the comments!

Happy Coding!