MVC – Action Result Methods
Action Method
·
All the public methods of a Controller
class are called Action methods. They are like any other normal methods with
the following restrictions:
o
Action method must be public. It cannot be
private or protected
o
Action method cannot be overloaded
o
Action method cannot be a static method.
Default
Action Method:
·
Every controller can have default action
method as per configured route in RouteConfig class. By default, Index is a
default action method for any controller, as per configured default root as
shown below.
|
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}/{name}",
defaults: new { controller = "Home",
action = "Index",
id = UrlParameter.Optional
});
|
ActionResult
·
MVC framework includes various result
classes, which can be return from an action method. There result classes represent
different types of responses such as html, file, string, json, JavaScript etc.
The following table lists all the result classes available in ASP.NET MVC.
|
Result Class
|
Description
|
|
ViewResult
|
Represents HTML and markup. Renders a specified view to the
response stream
|
|
EmptyResult
|
Represents No response. An empty response is returned
|
|
ContentResult
|
Represents string literal. Writes content to the response
stream without requiring a view
|
|
FileContentResult/ FilePathResult/ FileStreamResult
|
Represents the content of a file. Returns a file to the client.
Returns a file to the client, which is provided by a Stream. Returns a file
to the client
|
|
JavaScriptResult
|
Represent a JavaScript script. Returns a piece of JavaScript
code that can be executed on the client
|
|
JsonResult
|
Represent JSON that can be used in AJAX. Serializes a given
object to JSON format
|
|
RedirectResult
|
Represents a redirection to a new URL. Performs an HTTP
redirection to a specified URL
|
|
RedirectToRouteResult
|
Represent another action of same or other controller. Performs
an HTTP redirection to a URL that is determined by the routing engine, based
on given route data
|
|
PartialViewResult
|
Returns HTML from Partial view. Renders a specified partial
view to the response stream
|
|
HttpUnauthorizedResult
|
Returns HTTP 403 status
|
·
The ActionResult class is a base class of
all the above result classes, so it can be return type of action methods which
returns any type of result listed above. However, you can specify appropriate
result class as a return type of action method.
|
Result Class
|
Description
|
Base Controller method
|
|
ViewResult
|
Represents HTML and markup.
|
View()
|
|
EmptyResult
|
Represents No response.
|
|
|
ContentResult
|
Represents string literal.
|
Content()
|
|
FileContentResult,
FilePathResult, FileStreamResult |
Represents the content of a file
|
File()
|
|
JavaScriptResult
|
Represent a JavaScript script.
|
JavaScript()
|
|
JsonResult
|
Represent JSON that can be used in AJAX
|
Json()
|
|
RedirectResult
|
Represents a redirection to a new URL
|
Redirect()
|
|
RedirectToRouteResult
|
Represent another action of same or other controller
|
RedirectToRoute()
|
|
PartialViewResult
|
Returns HTML
|
PartialView()
|
|
HttpUnauthorizedResult
|
Returns HTTP 403 status
|
·
Any action in an MVC controller, generally
speaking, returns an ActionResult. Obviously that class represents an action of
some kind.
|
public ActionResult Index()
{
return View();
}
|
·
An ActionResult in asp.net mvc is an
Abstract class and ActionResult is return type of controller method. The class
itself inherits from System.Object, and only adds one additional abstract
method: ExecuteResult, which is an abstract method that the derived classes of
ActionResult will implement themselves.
·
Each ActionResult return different type of
result. If we want to display image in WebForms we need to create Imagehandler
for it but in Asp.net MVC we can use FileResult which is already built in
method.
Types of Action Results in ASP.NET MVC
·
ViewResult
o
ViewResult returns a view.
|
public class HomeController : Controller
{
public ViewResult Index()
{
return View();
}
}
|
o
Since MVC follows
convention-over-configuration, MVC will look for a View named "Index"
in the Views/Home subfolder, and then look in Views/Shared if it doesn't find
it (and will throw an InvalidOperationException if it can't find it at all).
·
PartialViewResult
o
We can also specify an action to return a
partial view instead of a regular view. It returns a partial view to the
response.
|
public PartialViewResult Partial()
{
return PartialView("LoginPartial");
}
|
·
FileResult
o
If we want to return a file, this is the
ActionResult we use. Depending on which overload we pick, we can specify what
action the browser is to take with the downloaded file. For example, if we just
specify a URL and a MIME type, the browser attempts to display the file
specified. It returns binary file content to the response.
|
public FileResult ViewFile()
{
return File(Url.Content("~/Files/testfile.txt"), "text/plain");
}
|
o
Another overload will specify a download
name, and using this overload causes the browser to download the file, rather
than just display it
|
public FileResult DownloadFile()
{
return File(Url.Content("~/Files/testfile.txt"), "text/plain", "testFile.txt");
}
|
·
ContentResult
o
ContentResult is used when we want to allow
the action to specify what should be returned. It's a sort of catchall for
scenarios where we need to allow the action full control over the returned
content. All we need to do is specify the content and MIME type.
|
public ContentResult Content()
{
return Content("<h3>Here's
a custom content header</h3>", "text/html");
}
|
o
Calling this action will display the h3 tag
in the browser.
|
public string Content()
{
return "<h3>Here's
a custom content header</h3>";
}
|
o
MVC actually creates a ContentResult and
wraps it around the returned value (and it doesn't have to be a string). Unless
you return null, in which case MVC returns an EmptyResult.
·
EmptyResult
o
MVC wants you to use EmptyResult when the
action is specifically intended to return nothing. Unlike all of the previous
ActionResults though, EmptyResult doesn't have a helper. Additionally, if an
action returns null, MVC will detect that and make it return an EmptyResult.
|
public EmptyResult Empty()
{
return new EmptyResult();
}
public ActionResult NothingReturned()
{
return null; //Returns an
EmptyResult
}
|
·
JsonResult
o
JsonResult is used to represent
JSON-encoded data, which is most commonly used to return structured data to a
calling script, especially in AJAX scenarios.
|
public JsonResult Json()
{
return Json(new { Name = "John
Smith", ID = 4, DateOfBirth = new DateTime(1999, 12, 31) });
}
|
o
That returns a JSON structure that looks
like this:
§ {"Name":"John
Smith","ID":4,"DateOfBirth":"\/Date(946623600000)\/"}
o
Problems with JSON dates aside, the implications
of this are staggering. Since that just encoded an anonymous object, it follows
that JsonResult can handle any object, including user-defined ones, and encode
them into the JSON format.
|
public JsonResult Json()
{
return Json(new { Name = "John
Smith", ID = 4, DateOfBirth = new DateTime(1999, 12, 31) }, JsonRequestBehavior.AllowGet);
}
|
o
JsonRequestBehavior.AllowGet does exactly
what it sounds like; it allows browsers to access this JSON information in a
GET request. I'd only recommend turning this on if you know what you are doing,
since it could potentially expose you to JSON Hijacking.
·
JavaScriptResult
o
Another potentially dangerous ActionResult
is the JavaScriptResult, which returns script that is to be executed by the
browser.
|
public JavaScriptResult LoadScript()
{
return JavaScript("alert('Hello! This popup shows that we can return
JavaScript from controller actions.')");
}
|
·
RedirectResult
o
If we want to redirect to a URL, then we
can use RedirectResult
o
That works great for redirecting to outside
sites from the current app, but not so much for redirecting to other pages
within the same app. For that, we can use RedirectToRouteResult.
|
public RedirectResult
RedirectToOtherSite()
{
return Redirect("http://www.google.com");
}
|
·
RedirectToRouteResult
o
RedirectToRouteResult is used whenever we
need to go from one action to another. There are two different ways of using
it. One is to create your own Route values using RedirectToRoute:
|
public RedirectToRouteResult RedirectToRoute()
{
return RedirectToRoute(new { controller = "Home", action = "Route" });
}
|
|
public RedirectToRouteResult
RedirectToAction()
{
return RedirectToAction("Action");
}
|
o
RedirectToAction follows the same
convention-over-configuration idea from ViewResult; namely, that it looks for a
corresponding action in the current controller if you don't specify which
controller to look in.
o
RedirectToAction has many overloads that
allow you to specify controllers, actions, route values, etc. It's probably the
second most common ActionResult derived class, because it's so readable.
·
HttpStatusCodeResult
o
HttpStatusCodeResult return an HTTP status
code to the browser, along with a custom message to be displayed:
|
public HttpStatusCodeResult
UnauthorizedStatusCode()
{
return new HttpStatusCodeResult(HttpStatusCode.Unauthorized, "You are
not authorized to access this controller action.");
}
public HttpStatusCodeResult BadGateway()
{
return new HttpStatusCodeResult(HttpStatusCode.BadGateway, "I have no
idea what this error means.");
}
|
·
HttpUnauthorizedResult
o
Returning an HttpUnauthorizedResult is the
same as returning HttpStatusCodeResult with HttpStatusCode.Unauthorized, it's
just more readable:
|
public HttpStatusCodeResult
UnauthorizedResult()
{
return new HttpUnauthorizedResult("You are
not authorized to access this controller action.");
}
|
·
HttpNotFoundResult
o
This is also an overload of
HttpStatusCodeResult, but unlike HttpUnauthorizedResult, it actually does have
a helper method
|
public HttpNotFoundResult NotFound()
{
return HttpNotFound("We didn't
find that action, sorry!");
}
|
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