Populating complex objects from view, on post, using interfaces - asp.net-mvc

Question

I'm trying to post data from a bunch of text fields using the following:
Controller:
[HttpGet]
public ActionResult Order()
{
OrderViewModel vm = new OrderViewModel();
vm.Id = "some id";
List<IOrderItem> itemList= new List<IOrderItem>();
for (int i = 0; i <= 10; i++)
{
OrderItem x = new OrderItem();
x.ItemId = i + "";
itemList.Add(x);
}
vm.OrderItemList = itemList;
return View(vm);
}
[HttpPost]
public IActionResult Order(OrderViewModel model)
{
return View("blabla");
}
These are the models:
public class OrderViewModel : B.IOrderItemViewModel
{
private List<IOrderItem> orderItems;
public List<IOrderItem> OrderItemList
{
get { return orderItems; }
set { orderItems = value; }
}
private string orderId;
public string Id
{
get { return orderId; }
set { orderId = value; }
}
}
public class OrderItem : IOrderItem
{
private string orderItemId;
public string ItemId
{
get { return orderItemId; }
set { orderItemId = value; }
}
private string _description;
public string Description
{
get { return _description; }
set { _description = value; }
}
}
this is the view:
#model OrderViewModel
#using (Html.BeginForm("Order", "Home", FormMethod.Post))
{
#for (int i = 0; i < Model.OrderItemList.Count; i++)
{
#Html.HiddenFor(x => x.OrderItemList[i].ItemId)
#Html.TextBoxFor(x => x.OrderItemList[i].Description)
<br />
}
<input type="submit" value="submit" />
}
Here is the problem - The interfaces are in another project, let's call it B. I reference B in the project.json file for the main project, A. In B, I just defined the two interfaces the are inherited above.
If I do not use any interfaces, and I just use the objects
e.g. instead of :
List<IOrderItem> OrderItemList
I use :
List<OrderItem> OrderItemList
When I run the project, and hit the view, I see the textboxes. I fill in some data and hit submit. It goes to the controller as expected. If I put a breakpoint in the HttpPost actionresult method, and look at the model, I can see all the data I entered. Perfect.
If I use the code above, where I am inheriting from some interfaces, it does not work. The view loads, I enter in some data, I post, it hits the breakpoint, but the model is empty and it's all null.
Any ideas / help would be greatly appreciated!

Answer 1

You cant bind to interfaces. The process of model binding involves first initializing your model (internally the DefaultModelBinder uses Activator.CreateInstance()) , but you can't initialize an interface (how would it know which type to initialize), which is why
public List<OrderItem> OrderItemList { get; set; }
works, but
public List<IOrderItem> OrderItemList { get; set; }
wont.
This article discusses it more detail and includes a section on creating a custom Abstract Model Binder that may solve your problem.