How to pass model to partial view

Question

I have two view models:

public class ParentViewModel
    {
        public Id { get; set; }
        .....
        public ChildViewModel Child{ get; set; }
    }

public class ChildViewModel
    {
        public ChildId { get; set; }
        .....
    }

Controllers:

    public ActionResult Index()
        {
            .... <some code>
            return View("NewIndex", ParentViewModel);
        }

    [HttpPost]
    public ActionResult PartialAction(ChildViewModel childView)
    {
        return RedirectToAction("Index");
    }

And views: Index

@model ParentViewModel
....
@Html.Partial("_Partial", Model.Child)

and _Partial

@model ChildViewModel
... do some stuff with child model

When I'm trying to open Index page I've got an error:

The model item passed into the dictionary is of type 'ParentViewModel', but this dictionary requires a model item of type 'ChildViewModel'.

Why it tries to pass ParentViewModel instead of ChildViewModel. What I'm doing wrong?

Answer 1

I had the same issue as the OP. From one of the comments, I realized that the second parameter shouldn't be null, i.e from

@model ParentViewModel
@Html.Partial("_Partial", Model.Child)

If Model.Child is null, then Model is passed instead of Model.Child. If there will be cases when the second parameter is null, then you will have to check first in your code and maybe pass an initialized Child as the second parameter. Something like this

@Html.Partial("_Partial", new Child())

Answer 2

The answer is that needs to pass an empty object to Partial, like

@Html.Partial("_Partial", new ChildViewModel ())

Answer 3

You could return PartialView("...") from a Controller instead, and call the action from the Index view.

Controllers:

public ActionResult Index()
{
    .... <some code>
    return View("NewIndex", ParentViewModel);
}

public ActionResult Partial(ChildViewModel cvm)
{
    var vm = cvm ?? new ChildViewModel(); //if cvm from the parent view is null, return new cvm
    return PartialView("_Partial", vm) //return partial view
}

[HttpPost]
public ActionResult PartialAction(ChildViewModel childView)
{
    return RedirectToAction("Index");
}

And Index

@model ParentViewModel
....
@Html.Action("Partial", Model.Child)

Alternatively, you could initialize ParentViewModel in the Index() public ActionResult Index()

{
    .... <some code>
    return View("NewIndex", new ParentViewModel{Child = new ChildViewModel});
}