In standard ASP.NET MVC, you may be accustomed to seeing RedirectToAction. This allows you to specify a controller and action to redirect to, as well as any additional parameters you might want to pass along. In the following example, the VoteForCar action (which is triggered by submitting a form post) performs some voting logic, and then redirects to a generic Confirmation action (to which it also passes an id parameter). This action returns a thank-you view with additional fun facts about the car that you just voted for, which it retrieves using the ID that the RedirectToAction supplied.

[HttpPost]
public ActionResult VoteForCar(int id, string voterName) {
     
    // Voting logic
 
    RedirectToAction("Confirmation", new { carID = id });
}
 
public ActionResult Confirmation(int carID) {
 
    var fact = GetRandomFunFact(carID);
 
    return View(fact);
}

But you can’t use RedirectToAction in Sitecore

In Sitecore, you cannot use RedirectToAction. If VoteForCar was a controller rendering action, you might think that using RedirectToAction would simply refresh the page and change the output of that particular controller rendering to the result of the Confirmation. This is not the case. Instead, using RedirectToAction will interrupt the rendering of the Sitecore page and take you to the plain ASP.NET MVC view being output by the Confirmation action.

However, you can still use RedirectToRoute — and it is possible to pass along parameters in exactly the same way.

[HttpPost]
public ActionResult VoteForCar(int id, string voterName) {
     
    // Voting logic
 
    var options = new UrlOptions
    {
        AddAspxExtension = false,
        LanguageEmbedding = LanguageEmbedding.Never
    };
 
    var pathInfo = (LinkManager.GetItemUrl(Sitecore.Context.Database.GetItem(new ID("{81B81009-4C09-4D31-88A0-4486A7FE35E0}")), options));
 
        return RedirectToRoute(MvcSettings.SitecoreRouteName, new { pathInfo = pathInfo.TrimStart(new char[] { '/' }), carID = id });
    }
}

At the very least, RedirectToRoute requires pathInfo to be set to the URL of the Sitecore item that you wish to redirect to. I have removed the .aspx extension and language embedding using UrlOptions, but you can change these settings globally on the linkManager in web.config instead.

Keep in mind that any controller rendering on the page that you are redirecting to will be able to access the carID parameter. Let’s say you have a ‘Confirmation’ controller rendering that maps to the Confirmation action result. If there is a carID in the query string, it will output a fun fact about the car you selected — if not, it will just say ‘Thank you for voting!‘.

But what happens if an editor — using the Page Editor — adds an additional component to the confirmation page, and it also relies on a carID parameter — but for different reasons? Doesn’t matter — the new component detects that carID exists in the query string and uses it anyway.

Given that you cannot predict which components will appear on a page, it is probably wise to give your parameter a more unique name:

public ActionResult Confirmation(int carFunFactID) {
 
    var fact = GetRandomFunFact(carID);
 
    return View(fact);
}

You should also make sure that your action result is able to cope with a null or empty value.

What kind of values can I pass between actions?

Just like in regular ASP.NET MVC, you cannot pass complex types — like complete models — between actions. RedirectToRoute is a redirect, and basically acts as a plain old HTTP GET — with ?carID=434 in the URL.

(Thank you @HoseyBeast for the ASP.NET MVC help.)