Nested objects in view model confuses MVC 4 routing? - asp.net-mvc-4

Question

So I have this view and it's generated by CMS. The brains of the view are in another view rendered by RenderAction.
Up until now it has looked like this:
Main.cshtml
<div>CMS content</div>
#{
var myContent = new MainContentModel() {
SomethingUsedFurtherDown = "Easier for CMS people to edit"
}
Html.RenderAction("_Main", "Foo", new { arg1 = "this", arg2 = "that", content = myContent });
}
MainContentModel.cs
namespace MyApp.Services.ViewModels.Foo
{
public class MainContentModel
{
public string SomethingUsedFurtherDown { get; set; }
}
}
MainViewModel.cs
namespace MyApp.Services.ViewModels.Foo
{
public class MainViewModel
{
public string Arg1 { set; set; }
public string Arg2 { set; set; }
public string Name { get; set; }
public string Age { get; set; }
public string Address { get; set; }
public MainContentModel Content { get; set; }
}
}
_Main.cshtml
#model MyApp.Services.ViewModels.Foo.MainViewModel
#Html.EditorFor(m => m.Name)
#Html.EditorFor(m => m.Age)
#Html.EditorFor(m => m.Address)
<!-- whatever - doesn't matter -->
FooController.cs
namespace My.App.Controllers
{
using System;
using System.Web.Mvc;
public class FooController
{
public ActionResult Main(string arg1, string arg2, MainContentModel cm)
{
var vm = new MainViewModel() { Arg1 = arg1, Arg2 = arg2, Content = cm };
return this.View("_Main", vm);
}
}
}
All works fine. So why am I bothering you? Well, this isn't the real code, obviously. There are many more arguments to the controller method and it's all getting rather messy. So I figured I would pass in the view model from the outer view.
Main.cshtml
<div>CMS content</div>
#{
var myVM = new MainViewModel() {
Arg1 = "this"
, Arg2 = "that"
, Content = new MainContentModel() {
SomethingUsedFurtherDown = "Easier for CMS people to edit"
}
};
Html.RenderAction("_Main", "Foo", new { vm = myVM });
}
...and just have one argument to the controller method
FooController.cs
namespace My.App.Controllers
{
using System;
using System.Web.Mvc;
public class FooController
{
public ActionResult Main(MainViewModel vm)
{
return this.View("_Main", vm);
}
}
}
And that's where the trouble starts. I get this error:
The view '_Main' or its master was not found or no view engine supports the searched locations. The following locations were searched:
~/Views/Foo/_Main.aspx
~/Views/Foo/_Main.ascx
~/Views/Shared/_Main.aspx
~/Views/Shared/_Main.ascx
~/Views/Foo/_Main.cshtml
~/Views/Foo/_Main.vbhtml
~/Views/Shared/_Main.cshtml
~/Views/Shared/_Main.vbhtml
~/Views/CMS/_Main.cshtml
~/Views/CMS/Foo/_Main.cshtml
But if I remove the initialisation of the content model, it all works again. Well, okay, it doesn't work work. But the error goes away, leaving me to come up with the obvious solution of adding the content model to the argument list and assigning it to the view model in the controller method.
Main.cshtml
<div>CMS content</div>
#{
var myVM = new MainViewModel() {
Arg1 = "this"
, Arg2 = "that"
};
var myCm = new MainContentModel() {
SomethingUsedFurtherDown = "Easier for CMS people to edit"
};
Html.RenderAction("_Main", "Foo", new { vm = myVM, cm = myCm });
}
FooController.cs
namespace My.App.Controllers
{
using System;
using System.Web.Mvc;
public class FooController
{
public ActionResult Main(MainViewModel vm, MainContentModel cm)
{
vm.Content = cm;
return this.View("_Main", vm);
}
}
}
Which is fine except that there are quite a few child objects of the real view model and I don't want to separate those out into arguments - it defeats the purpose of what is supposed to be a tidying up exercise.
Question
Is MVC4 supposed to be binding the child objects seamlessly and this is a bug? Or does it just not work this way and my only choice is to separate them out into extra parameters as above?
Cheers,
.pd.

Answer 1

Just in case anybody else has fallen into this trap. The problem was not the model binding. MVC 4 binds nested objects just fine. I was missing the subtlety of the error. The standard here is to prefix the "real" view name with an underscore and it was this that was not being found. The failure was occurring here:
return this.View("_Main");
What I didn't include in my post (cuz if I'd remembered, that would've fixed it!) was the fact that in the real situation the RenderAction looks like this:
RenderAction("Main", "Foo", new { area = "SomeArea", ... });
And I had missed off the area in my refactoring. Pretty embarrassing but if it stops somebody else beating their head against the wall then the shame will have been worth it :-)