MVC Model Instantiation

Question

I'm not grasping some conceptual basics with MVC models and I'm hoping for some helpful clarification.

In my MVC 4 web app, I have a view model that builds an IEnumerable<SelectListItem> for a DropDownList, and if I do this in my view:

@model MyApp.Models.MyModel

@Html.DropDownListFor(x => x.MyThingID, Model.MySelectList, "Select...")

I get an "Object reference not set to an instance of an object" error.

But if I do this:

@model MyApp.Models.MyModel

@{ var myModel = new MyApp.Models.MyModel(); }
@Html.DropDownListFor(x => x.MyThingID, myModel.MySelectList, "Select...")

It works. But this explicit instantiation looks and feels terribly wrong to me, and I'm not sure if I should be doing anything in the controller, which at this point is just a bare-bones "return View()" ActionResult.

I can't find much good guidance and ultimately I'm trying to implement some cascading dropdowns, so I need to get a better grasp on how this works. If you have the time and inclination to assist, I'd greatly appreciate it.

Answer 1

You should pass the model to the view. You can do this in the controller code:

return View(myModel);

instead of

return View(); // without the model!

where yourmodel is typeof MyApp.Models.MyModel. Just init it and pass it.

public ActionResult YourAction()
{
    var myModel = new MyApp.Models.MyModel();
    // do other actions or put more data inside myModel
    return View(myModel);
}