ASP MCV: Index action with optional string parameter

Question

I would like to have an Index action with an optional string parameter. I'm unable to make it work.

I need the following routes:

http://mysite/download
http://mysite/download/4.1.54.28

The first route will send a null model to the Index view, and the second one will send an string with the version number.

How can I define the route and the controller?

This is my route definition:

routes.MapRoute(
    name: "Download",
    url: "Download/{version}",
    defaults: new { controller = "Download", action = "Index", version = UrlParameter.Optional }
);

 routes.MapRoute(
    name: "Default",
    url: "{controller}/{action}/{id}",
    defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);

And this is the controller:

    public ActionResult Index(string version)
    {
        return View(version);
    }

Why does this not work? I'm not an expert in ASP MVC but this seems to be a very simple problem.

The error

• When I go to http://mysite/downloads it works fine
• When I go to http://mysite/downloads/4.5.6, the controller is correctly called, and the parameter is correctly passed. But then seems that the view is not found. This is the error I found:

Answer 1

string? will not work because string is not a value type.

You can set a default value to your parameter:

public ActionResult Index(string version="")
{
    return View(version);
}

Answer 2

The issue is fixed passing the parameter to the view in the following way:

public ActionResult Index(string version)
{
    return View((object)version);
}

Or

public ActionResult Index(string version)
{
    return View("Index", version);
}

When you pass a string model to the view, if the model is a string parameter, it is interpreted as the view name due to the following overload method

View(String viewName)