Url Form Action Without ViewContext

Question

Is it possible to get a URL from an action without knowing ViewContext (e.g., in a controller)? Something like this:

LinkBuilder.BuildUrlFromExpression(ViewContext context, Expression<Action<T>> action)

...but using Controller.RouteData instead of ViewContext. I seem to have metal block on this.

Answer 1

Here's how I do it in a unit test:

    private string RouteValueDictionaryToUrl(RouteValueDictionary rvd)
    {
        var context = MvcMockHelpers.FakeHttpContext("~/");
        // _routes is a RouteCollection
        var vpd = _routes.GetVirtualPath(
            new RequestContext(context, _
                routes.GetRouteData(context)), rvd);
        return vpd.VirtualPath;
    }

Per comments, I'll adapt to a controller:

string path = RouteTable.Routes.GetVirtualPath(
    new RequestContext(HttpContext, 
        RouteTable.Routes.GetRouteData(HttpContext)),
    new RouteValueDictionary( 
        new { controller = "Foo",
              action = "Bar" })).VirtualPath;

Replace "Foo" and "Bar" with real names. This is off the top of my head, so I can't guarantee that it's the most efficient solution possible, but it should get you on the right track.

Answer 2

Craig, Thanks for the correct answer. It works great, and it also go me thinking. So in my drive to eliminate those refactor-resistent "magic strings" I have developed a variation on your solution:

public static string GetUrlFor<T>(this HttpContextBase c, Expression<Func<T, object>> action)
    where T : Controller
{
    return RouteTable.Routes.GetVirtualPath(
        new RequestContext(c, RouteTable.Routes.GetRouteData(c)), 
        GetRouteValuesFor(action)).VirtualPath;
}

public static RouteValueDictionary GetRouteValuesFor<T>(Expression<Func<T, object>> action) 
    where T : Controller
{
    var methodCallExpresion = ((MethodCallExpression) action.Body);
    var controllerTypeName = methodCallExpresion.Object.Type.Name;
    var routeValues = new RouteValueDictionary(new
    {
        controller = controllerTypeName.Remove(controllerTypeName.LastIndexOf("Controller")), 
        action = methodCallExpresion.Method.Name
    });
    var methodParameters = methodCallExpresion.Method.GetParameters();
    for (var i = 0; i < methodParameters.Length; i++)
    {
        var value = Expression.Lambda(methodCallExpresion.Arguments[i]).Compile().DynamicInvoke();
        var name = methodParameters[i].Name;
        routeValues.Add(name, value);
    }
    return routeValues;
}

I know what some will say...dreaded reflection! In my particular application, I think the benefit of maintainability outweighs performance conerns. I welcome any feedback on this idea and the code.