ASP.Net MVC RouteData and arrays

Question

If I have an Action like this:

public ActionResult DoStuff(List<string> stuff)
{
   ...
   ViewData["stuff"] = stuff;
   ...
   return View();
}

I can hit it with the following URL:

http://mymvcapp.com/controller/DoStuff?stuff=hello&stuff=world&stuff=foo&stuff=bar

But in my ViewPage, I have this code:

<%= Html.ActionLink("click here", "DoMoreStuff", "MoreStuffController", new { stuff = ViewData["stuff"] }, null) %>

Unfortunately, MVC is not smart enough to recognize that the action takes an array, and unrolls the list to form the proper url route. instead it just does a .ToString() on the object which just lists the data type in the case of a List.

Is there a way to get Html.ActionLink to generate a proper URL when one of the destination Action's parameters is an array or list?

-- edit --

As Josh pointed out below, ViewData["stuff"] is just an object. I tried to simplify the problem but instead caused an unrelated bug! I'm actually using a dedicated ViewPage<T> so I have a tightly coupled type aware Model. The ActionLink actually looks like:

<%= Html.ActionLink("click here", "DoMoreStuff", "MoreStuffController", new { stuff = ViewData.Model.Stuff }, null) %>

Where ViewData.Model.Stuff is typed as a List

Solution 1

I'm thinking that a custom HtmlHelper would be in order.

 public static string ActionLinkWithList( this HtmlHelper helper, string text, string action, string controller, object routeData, object htmlAttributes )
 {
     var urlHelper = new UrlHelper( helper.ViewContext.RequestContext );


     string href = urlHelper.Action( action, controller );

     if (routeData != null)
     {
         RouteValueDictionary rv = new RouteValueDictionary( routeData );
         List<string> urlParameters = new List<string>();
         foreach (var key in rv.Keys)
         {
             object value = rv[key];
             if (value is IEnumerable && !(value is string))
             {
                 int i = 0;
                 foreach (object val in (IEnumerable)value)
                 {
                     urlParameters.Add( string.Format( "{0}[{2}]={1}", key, val, i ));
                     ++i;
                 }
             }
             else if (value != null)
             {
                 urlParameters.Add( string.Format( "{0}={1}", key, value ) );
             }
         }
         string paramString = string.Join( "&", urlParameters.ToArray() ); // ToArray not needed in 4.0
         if (!string.IsNullOrEmpty( paramString ))
         {
            href += "?" + paramString;
         }
     }

     TagBuilder builder = new TagBuilder( "a" );
     builder.Attributes.Add("href",href);
     builder.MergeAttributes( new RouteValueDictionary( htmlAttributes ) );
     builder.SetInnerText( text );
     return builder.ToString( TagRenderMode.Normal );
}

Solution 2

Combining both methods works nicely.

public static RouteValueDictionary FixListRouteDataValues(RouteValueDictionary routes)
{
    var newRv = new RouteValueDictionary();
    foreach (var key in routes.Keys)
    {
        object value = routes[key];
        if (value is IEnumerable && !(value is string))
        {
            int index = 0;
            foreach (string val in (IEnumerable)value)
            {
                newRv.Add(string.Format("{0}[{1}]", key, index), val);
                index++;
            }
        }
        else
        {
            newRv.Add(key, value);
        }
    }

    return newRv;
}

Then use this method in any extension method that requires routeValues with IEnumerable(s) in it.

Sadly, this workaround seams to be needed in MVC3 too.