Object reference error using Partial Views

问题:

I am getting the ubiquitous "object reference" error and don't know how to resolve it. I believe it has to do with calling a partial view. I am using a jquery wizard, so the partial views are the "steps" in the wizard that get displayed.

In my main .cshtml view I do this (I'm leaving out the HTML):

@using MyNamespace.Models
@using MyNamespace.ViewModels
@model MyViewModel
...
...
using (Html.BeginForm())
{
    ...
    // this works inside MAIN view (at least it goes through 
    // before I get my error)
    if (Model.MyModel.MyDropDown == DropDownChoice.One)
    {
         //display something
    }
    ...
    // here i call a partial view, and in the partial view (see
    // below) I get the error
    @{ Html.RenderPartial("_MyPartialView"); }
    ...
}

The above works (at least it goes through before I get to my error).

Here is my partial view (again, leaving out HTML):

@using MyNamespace.Models
@using MyNamespace.ViewModels
@model MyViewModel
....
// I get the object reference error here
@if (Model.MyModel.MyRadioButton == RadioButtonChoice.One)
{
    // display something
}
....

I am confused because with the exception of the @if vs. if, it's essentially the same code. I do not know what I've done wrong, or how to fix.

For context, here is MyViewModel:

public class MyViewModel
{
    public MyModel MyModel { get; set; }
}

And the MyDropDown and MyRadioButton are using enums thusly:

public enum DropDownChoice { One, Two, Three }
public enum RadioButtonChoice { One, Two, Three }

public DropDownChoice? MyDropDown { get; set; }
public RadioButtonChoice? MyRadioButton { get; set; }

My controller only has an action for the main form and no actions for the partial view:

public ActionResult Form()
{
    return View("Form");
}

[HttpPost]
public ActionResult Form(MyViewModel model)
{
    if (ModelState.IsValid)
    {
        return View("Submitted", model);
    }
    return View("Form", model);
}

Any thoughts? Is it that I have to create an ActionResult for that partial view even though there is no direct call to it (other than as a partial view in the wizard)? Thank you.

回答1:

Your partial requires a model

@model MyViewModel

You either need to pass a model

@{ Html.RenderPartial("_MyPartialView", MyViewModel);

Or use a child Action and call your partial with the

@Action("_MyPartialView");

with corresponding Action

    public ActionResult _MyPartialView()
    {

        MyViewModel model = new MyViewModel();
        return View(model)
    }