将PartialView链接到View返回System.Web.Mvc.WebViewPage <TModel> .Model.get返回null

Question

I looked up everywhere and tried multiple solutions but none of them would work. In my MVC website, I have a cart section and a checkout section. I want to make it so inside my checkout section, i have a small cart section to show the cart.

This is my partial view _CartItems.cshtml

@model IEnumerable<ArrowDefenseSystems.Models.Cart>
@{
    ViewBag.Title = "Your Cart";
}
@if (Model != null)
{
    foreach (var item in Model)
    {
        <div class="itemInfo row">
            <img class="col-md-3" src="@Url.Content("~/Content/" + @Html.DisplayFor(modelItem => item.productImage))" height="100px">
            <div class="CartItemText col-md-9">
                <h3>@Html.DisplayFor(modelItem => item.productName)</h3>
                <i>$@Html.DisplayFor(modelItem => item.productPrice)</i><br>
                Quantity : @Html.DisplayFor(modelItem => item.quantityChosen)<br>
            </div>
        </div>
        <hr />
    }
}

When I launch the Partial View by itself, it shows the items fine and everything runs correctly.

This is how I'm linking the partial view to the view Checkout.cshtml

@model ArrowDefenseSystems.Models.ParentViewModel
...
...
@Html.Partial("_CartItems", Model.Cart)

When I run this code i get the following error on the code above:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

System.Web.Mvc.WebViewPage<TModel>.Model.get returned null.

ParentViewModel:

public class ParentViewModel
{
   public Checkout Checkout { get; set; }
   public Cart Cart { get; set; }
}

Checkout Controller (theres more but its unnecessary):

[HttpGet]
public ActionResult _CartItems()
{
  return PartialView(db.Carts.ToList());
}
public ActionResult Checkout()
{

   return View();

}

I've tried many solutions but all return the same error. What am I missing?

Answer 1

I think there is a fundamental misunderstanding here: @Html.Partial("_CartItems", Model.Cart) will not call your _CartItems() action. Instead, it will create a new instance of the _CartItems.cshtml partial view, and use your Model.Cart parameter as it's Model .

In this case, there are two problems:

• _CartItems.cshtml is expecting a model with a type of IEnumerable<ArrowDefenseSystems.Models.Cart> , whereas you are passing it a model with a type of Cart (via the Model.Cart parameter)
• Model.Cart is not being instantiated in your Checkout action

So, to fix this, you should first change your ParentViewModel to be:

public class ParentViewModel
{
   public Checkout Checkout { get; set; }
   public IEnumerable<Cart> Carts { get; set; }
}

Then, update your Checkout action to be:

public ActionResult Checkout()
{
   var viewModel = new ParentViewModel
   {
       Carts = db.Carts.ToList()
   }

   return View(viewModel);
}

And change your usage of Model.Cart to Model.Carts (due to the rename above)

After that, you can remove your _CartItems action as it is no longer used.