复杂对象的MVC模型绑定Html.dropdownlistfor不起作用

Question

When i use simle model and pass in view example a copy of the model-everything worked well.

in controller

 AdvertisingStructure mc = context.AdvertisingStructures.Single(a => a.Id_show == id);
        if (mc == null)
        {
            return HttpNotFound();
        }

        return View(mc);

in view

 @model  Sciencecom.Models.AdvertisingStructure
 @Html.DropDownListFor(a => a.Owner.Id, new SelectList(owners, "id", "Name"))

the value of the list selected

But i inserted this model in complex objects and pass in view example a new copy-html.dropdownlist stopped working(the value of the list not selected )

new model

   public class CompositeModelForEdit
{
    public AdvertisingStructure Structure;

    public IEnumerable<Side> Sides;

    public IEnumerable<Surface> Surfaces;

} 

in controller

  AdvertisingStructure mc = context.AdvertisingStructures.Single(a => a.Id_show == id);
        List<Surface> surfaces=new List<Surface>();
        foreach (var sides in mc.Sides)
        {
            foreach (var surface in sides.Surfaces)
            {
                surfaces.Add(surface);
            }
        }
        return View(new CompositeModelForEdit() { Sides = mc.Sides, Structure = mc,Surfaces = surfaces});

in view

@model  CompositeModelForEdit
     @Html.DropDownListFor(a => a.Structure.Owner.Id, new SelectList(owners, "id", "Name"))

have any ideas(field input display value)?

Answer 1

Your models are different, yet in the SelectList you use the same properties - Id, Name. I'm guessing that your AdvertisingStructure class contains those properties, but the CompositeModelForEdit does not.

EDIT: First of all, do not use such a complicated viewmodel, use something simpler, for example:

public class OwnerViewModelForEdit
{
    public int OwnerId { get; set; }

    public string  Name { get; set; }

    //....
}

Then in your GET action, you can define your list of items that you want to appear in the dropdown:

IEnumerable<SelectListItem> ownersList =
            owners.Select(o => new SelectListItem() {Value = o.Id.ToString(), Text = o.Name});
ViewBag.Owners = ownersList;

return View(new OwnerViewModelForEdit(.........))

finally, in the view define your dropdownlist:

@Html.DropDownListFor(o => o.OwnerId, (IEnumerable<SelectListItem>)ViewBag.Owners)

And then in your POST action bind the viewmodel data to your respective Owner model and you are done.

There are many answers on Stackoverflow, regarding mvc dropdowns. If you search a bit, you will find an even better suggestions.