Action Methods

Learning objectives#

• Return the right ActionResult for each situation
• Restrict actions to GET or POST
• Return JSON safely from MVC 5
• Send files and status codes

Explanation#

Actions usually return ActionResult (or a more specific type). The helper methods on Controller build the results: View(), PartialView(), Content(), Json(), File(), Redirect(), RedirectToAction(), HttpNotFound() and new HttpStatusCodeResult(code).

[HttpGet] and [HttpPost] restrict which HTTP method an action answers. Two actions can share a name — Create() for GET shows the form and Create(model) for POST saves it.

Json(data) uses JavaScriptSerializer. For GET requests you must pass JsonRequestBehavior.AllowGet; MVC 5 blocks JSON over GET by default because of an old JSON-hijacking attack on arrays.

File(bytes, contentType, fileDownloadName) sends a download with a Content-Disposition header. RedirectToAction sends a 302 to another action’s URL, built from the routes.

[ActionName("delete")] exposes a method under a different name, which helps when GET and POST versions need the same URL but C# needs different signatures.

Syntax#

1return View(model);                                   // HTML page
2return Content("text", "text/plain");                 // raw text
3return Json(data, JsonRequestBehavior.AllowGet);      // JSON for GET
4return File(bytes, "text/csv", "orders.csv");          // download
5return RedirectToAction("Index");                     // 302
6return HttpNotFound();                                // 404
7return new HttpStatusCodeResult(400, "Bad id");       // any status

Code example: One controller, many kinds of results#

1// Controllers/CatalogController.cs
2using System.Net;
3using System.Text;
4using System.Web.Mvc;
5

6namespace ShopSite.Controllers
7{
8    public class CatalogController : Controller
9    {
10        // GET /Catalog/Price/1   → plain text
11        public ActionResult Price(int id)
12        {
13            if (id <= 0) return new HttpStatusCodeResult(HttpStatusCode.BadRequest, "id must be positive");
14            if (id > 3) return HttpNotFound();
15            return Content(
quot;Product {id} costs {id * 20} rupees", "text/plain");
16        }
17

18        // GET /Catalog/Info/2   → JSON
19        public ActionResult Info(int id)
20        {
21            var product = new { Id = id, Name = "Notebook", Price = 60.5m, Tags = new[] { "paper", "a4" } };
22            return Json(product, JsonRequestBehavior.AllowGet);
23        }
24

25        // GET /Catalog/Export   → file download
26        public ActionResult Export()
27        {
28            var csv = "Id,Name,Price\n1,Gel Pen,20\n2,Notebook,60.5\n";
29            return File(Encoding.UTF8.GetBytes(csv), "text/csv", "products.csv");
30        }
31

32        // GET /Catalog/Old   → permanent redirect
33        public ActionResult Old()
34        {
35            return RedirectToActionPermanent("Price", new { id = 1 });
36        }
37

38        // POST /Catalog/Remove/2 only
39        [HttpPost]
40        [ActionName("Remove")]
41        public ActionResult RemoveConfirmed(int id)
42        {
43            return RedirectToAction("Price", new { id });
44        }
45    }
46}

GET /Catalog/Price/2
200 OK
Product 2 costs 40 rupees

GET /Catalog/Price/9
404 Not Found

GET /Catalog/Price/0
400 id must be positive

GET /Catalog/Info/2
200 OK
Content-Type: application/json; charset=utf-8
{"Id":2,"Name":"Notebook","Price":60.5,"Tags":["paper","a4"]}

GET /Catalog/Export
200 OK
Content-Disposition: attachment; filename=products.csv
Id,Name,Price
1,Gel Pen,20
2,Notebook,60.5

GET /Catalog/Old
301 Moved Permanently → /Catalog/Price/1

GET /Catalog/Remove/2
404 Not Found

POST /Catalog/Remove/2
302 Found → /Catalog/Price/2

This example is illustrative. Copy or download it and run it in your own environment; the expected output is shown above.

Step-by-step explanation#

1. Price validates the id: 0 gives 400 with a reason, 9 gives 404, and 2 gives plain text.
2. Info returns Json(...), which serialises the anonymous object with JavaScriptSerializer — decimals stay as numbers and property names keep their PascalCase.
3. Export sends bytes with Content-Disposition: attachment, so the browser downloads products.csv.
4. Old answers 301 Moved Permanently, which tells browsers and search engines to update their links.
5. RemoveConfirmed only accepts POST and is exposed as Remove, so a GET to /Catalog/Remove/2 returns 404 while the POST redirects.

Real-world use case#

Common mistakes#

Best practices#

• Pick the most specific result: NotFound, BadRequest, Redirect
• Use [HttpPost] for anything that changes data
• Use RedirectToActionPermanent for moved pages (SEO)
• Return view models or DTOs in JSON, not EF entities

Remember this#

Practice exercise#

1// Controllers/ReceiptsController.cs
2using System.Text;
3using System.Web.Mvc;
4

5namespace ShopSite.Controllers
6{
7    public class ReceiptsController : Controller
8    {
9        public ActionResult Download(int id)
10        {
11            if (id > 1000) return HttpNotFound();
12            var text = 
quot;Receipt for order {id}";
13            return File(Encoding.UTF8.GetBytes(text), "text/plain", 
quot;receipt-{id}.txt");
14        }
15    }
16}

GET /Receipts/Download/42
200 OK
Content-Disposition: attachment; filename=receipt-42.txt
Receipt for order 42

GET /Receipts/Download/5000
404 Not Found

Mini quiz#

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