How to create a strongly typed master page using a base controller in ASP.NET MVC

Question

Following the NerdDinners example, I am interested in creating a strongly typed Master Page. In order to achieve this, I use a base controller which retrieves the data for the master page. All other controllers inherit this class. Similarly, I have ViewModels for the master page and any other views. The view ViewModel classes inherit from the master page's ViewModel.

Question

How should a child controller ensure that the master page's data is passed to the View without setting the properties of its ViewModel that pertain to the master page itself?

My the master page will display a number of buttons, which are determined in an XML file, hence the Buttons class that I am populating.

MasterPage ViewModel Code Snippet

using System.Collections.Generic;

namespace Site1.Models
{
    public class MasterViewModel
    {
        public List<Button> Buttons{set; get;}
    }
}

View ViewModel

namespace Site1.Models
{
    public class View1ViewModel : MasterViewModel
    {
        public SomeDataClass SomeData { get; set; }
    }
}

Base Controller

using System.Collections.Generic;
using System.Web.Mvc;
using Site1.Models;

namespace Site1.Controllers
{
    public abstract class BaseController : Controller
    {
        protected MasterViewModel model = new MasterViewModel();

        public BaseController()
        {
            model.Buttons = new List<Button>();
            //populate the button classes (doesn't matter how)
            PopulateButtons(model.Buttons);
        }
    }
}

View's controller:

using System.Web.Mvc;

namespace Site1.Controllers
{
    public class View1Controller : BaseController
    {
        public ActionResult Index()
        {
            Models.View1ViewModel viewModel = new Models.View1ViewModel();
            SomeDataClass viewData = new SomeDataClass()
            //populate data class (doesn't matter how)
            PopulateDataClass(viewData);
            viewModel.SomeData = viewData;
            //I WANT TO ELIMINATE THE FOLLOWING LINE!
            viewModel.Buttons = model.Buttons;
            return View("Index", viewModel);
        }
    }
}

The master page inherits System.Web.Mvc.ViewMasterPage<Site1.Models.MasterViewModel>.

The view inherits System.Web.Mvc.ViewMasterPage<Site1.Models.View1ViewModel>.

Answer 1

You could create an after action executed filter which looks for a model of that type and sets the properties accordingly, perhaps by calling a base controller function. You would then put the filter on the base class, and all actions would see it automatically.

The action filter attribute gets the controller's ViewModel, and passes it to the controller's SetModel function:

using System.Web.Mvc;
using Site1.Controllers;

namespace Site1.Models
{
    public class MasterAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            base.OnActionExecuted(filterContext);

            MasterViewModel viewModel = (MasterViewModel)((ViewResultBase)filterContext.Result).ViewData.Model;

            BaseController controller = (BaseController)filterContext.Controller;
            controller.SetModel(viewModel);
        }
    }
}

This function is added to the BaseController:

public void SetModel(MasterViewModel childViewModel)
{
    childViewModel.Buttons = model.Buttons;
}

Answer 2

Rather than creating an attribute, why not just override Controller.OnActionExecuted and put the initialization code there? Seems a bit simpler.

Answer 3

thanks, great solution! i have used it in my project and it works very well.

i think this pattern is the best ViewModel Pattern for asp.net mvc.

---

public void SetModel(MasterViewModel childViewModel)
{
    childViewModel.Buttons = model.Buttons;
}

maybe it should be:

public void SetModel(MasterViewModel childViewModel)
{
    model.Buttons = childViewModel.Buttons;
}