Render an ASP.Net MVC partial view to a string when the partial view contains a render action

Question

I have an error that has been running me up the walls the past couple of days. I have some code that takes an HttpContext and a ViewResult and renders the view into the string. This code seems to work very well, until I introduce a view that includes an @Html.RenderAction call. When the RenderAction call is added to the view, I get an error message stating that the controller tied to the action needs a parameter-less constructor. Adding such a constructor, however, does not improve the situation. The code that performs the render follows:

public static string Render(HttpContextBase httpContext, ViewResultBase partialViewResult)
{
    var routeData = new RouteData();
    routeData.Values.Add("controller", "mock");

    var context = new ControllerContext(httpContext, routeData, new EmptyController());

    var view = partialViewResult.View;
    if (view == null)
    {
        result = partialViewResult.ViewEngineCollection.FindPartialView(context, partialViewResult.ViewName);

        view = result.View;
    }

    using (var sw = new StringWriter())
    {
        var viewContext = new ViewContext(context, view, partialViewResult.ViewData,
                                      partialViewResult.TempData, sw);
        view.Render(viewContext, sw);
        if (result != null)
            result.ViewEngine.ReleaseView(context, view);

        return sw.ToString();
    }
}

In the view I am trying to render, I have tried:

@{ Html.RenderAction(FormController.Directive(Model.FormModel)); }

and

@Html.Action(FormController.Directive(Model.FormModel))

Both result in the same error messaging.

An error occurred when trying to create a controller of type 'FormController'. Make sure that the controller has a parameterless public constructor.

Removing the action call altogether gets rid of the error message.

The action in the controller looks like:

public virtual ActionResult Directive(FormModel model)
{
    model.MyProperty = "test";

    return View("FormView", model);
}

Any advice would be greatly appreciated.

UPDATE

I traced this problem to having some sort of tie to Unity. The render code works when I add an empty constructor and remove all of the other constructors. The other constructors included references to interfaces that are routed through Unity. I will need to learn more about Unity. There may be some functionality there that is replacing or destroying my controller's default constructor.

Answer 1

Html.Action声明应类似于以下内容：

@Html.Action("Directive", "Form", new { model = Model.FormModel })

Answer 2

/ add default constructor into your "FormModel" class, it will solve the problem /

public void FormModel()
    {

    }

Answer 3

As commented on earlier, the error is related to our use of Unity IOC. It looks like this is a known problem with MVC when using dependency injected controllers. There is a proposed fix on CodeProject: http://www.codeproject.com/Articles/99361/How-To-Use-Unity-Container-In-ASP-NET-MVC-Framewor

I will try this and hope that it corrects the problem for us.