Confusion between Redirect and RedirectToAction

Question

I'm studying for a MS certificate (70-515).
I'm a confused with what I find online and what I read in a practice test.
A few questions on SO state that using a RedirectToAction is sending the browser a 302, thus causing it to change it's url in the address bar.

But this is a question from 1 of the practice tests:

QUESTION:

The MVC Home controller currently has only the default Index action. The relevant code is shown in the following code example.

public ActionResult Index()
{
    ViewData["Message"] = "Hello!";
    return View();
}

You need to create an action named FindID that displays the ID parameter entered as part of the path. If the path does not include an ID parameter, ASP.NET must process the Index action without changing the URL in the browser's address bar, and must not throw an exception. Which code segment should you use?

CORRECT ANSWER:

public ActionResult FindID(int? id)
{
    if (!id.HasValue)
        return RedirectToAction("Index");
    ViewData["Message"] = "ID is " + id.ToString();
    return View();
}

EXPLANATION:

You can use the RedirectToAction form of ActionResult to cause MVC to process a different action from within an action. MVC abandons the current action and processes the request as if the route had led directly to the action you redirect to. Essentially, this is equivalent to calling Server.Transfer in a standard ASP.NET application.

The Redirect ActionResult sends an "HTTP Error 302 - Found" response to the browser, which causes the browser to load the specified URL. This changes the address that appears in the address bar.

So:
- Does a RedirectToAction leave the URL in browser untouched?
- Does a Redirect change the URL in browser?
- Is the explanation of the practice test correct? From that I understand that RedirectToAction does NOT do a 302.

Answer 1

You can use the RedirectToAction form of ActionResult to cause MVC to process a different action from within an action. MVC abandons the current action and processes the request as if the route had led directly to the action you redirect to. Essentially, this is equivalent to calling Server.Transfer in a standard ASP.NET application.

This is incorrect.

Both the RedirectToRouteResult (RedirectToAction) and RedirectResult perform a 302 redirect, resulting in the URL in the browser changing.

To return the Index result without changing the url the code would actually be:

public ActionResult FindID(int? id)
{
    if (!id.HasValue)
        return View("index");
    ViewData["Message"] = "ID is " + id.ToString();
    return View();
}

However, I would not recommended this approach. If I make a request to mysite.com/products/some-product and some-product does not exist, then I should inform the user of that with the relevant status code (also important for search engines).

If the sole purpose of your FindID action is to do something with the id parameter, then it should not be nullable/optional. This way the FindID action would not be invoked if an ID was not specified.