M-V-C: How to get or indicate Selected Items in List box in the Edit Mode?

Question

I am creating Multi-Select able List Box. I am able to successfully render items from model to list box. Following is my code:

Properties

public IEnumerable<SelectListItem> carTypes { get; set; }
public IEnumerable<string> selectedCarTypes { get; set; }

Create Action

public ActionResult Create()
{
     List<SelectListItem> selectListItem = new List<SelectListItem>();

     foreach(CarType type in db.CarTypes)
        {
            SelectListItem item = new SelectListItem()
            {
                Text = type.Name,
                Value = type.Id.ToString()
            };
            selectListItem.Add(item);
        }

        Assigning assign = new Assigning ();
        assign.carTypes = selectListItem;
        return View(assign);
}

View

@Html.ListBoxFor(model=>model.selectedCarTypes,Model.carTypes)

The problem is the edit action. I have been trying to highlight all the List box in the Edit View which are selected for the particular AssignId e.g. In list box there are three items: Hyundai, Toyota, and BMW and I select BMW and Toyota and Create Assigning. Now When I come back to Edit View it should highlight BMW and Toyota.

I took reference from here, but did not work for me. Is there any solution for this problem?

Modification: Here is my Edit Action

public ActionResult Edit(int? id)
{
     if (id == null)
     {
         return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
     }
     Assigning assign = db.Assigning.Find(id);
     if (assign == null)
     {
         return HttpNotFound();
     }
     return View(assign);
}

Answer 1

You are not setting up your models when Edit:

1. Model.carTypes should be List<SelectListItem> of all CarTypes and

2. Model.selectedTypes should be List<string> of all selected values