Question

I’m trying to bind a ListBox in my partial view but I’m getting the exception…

Object reference not set to an instance of an object.

Referencing @Html.ListBoxFor(x => x.SelectedRoles, Model.Roles)

I’m not sure what I’m doing wrong…

Model:

public class RegisterModel {
    public string UserName { get; set; }
    public string Email { get; set; }
    public string Password { get; set; }
    public string ConfirmPassword { get; set; }
    public string[] SelectedRoles { get; set; }
    public MultiSelectList Roles { get; set; }
}

Controller:

public class AdminController : Controller  {
    [ChildActionOnly]
    public ActionResult _AddUser() {
        var model = new RegisterModel {
            Roles = new MultiSelectList(Roles.GetAllRoles())
        };

        return View(model);
    }

}

PartialView _AddUser.cshtml:

@model RobotDog.Models.RegisterModel

@using(Html.BeginForm("_AddUser","Admin", FormMethod.Post)) {
    @Html.EditorFor(x => x.Email, new { @class = "input-xlarge", @placeholder = "Email"})
    @Html.EditorFor(x => x.UserName, new { @class = "input-xlarge", @placeholder = "User Name"})
    @Html.EditorFor(x => x.Password, new { @class = "input-xlarge", @placeholder = "Password"})
    @Html.ListBoxFor(x => x.SelectedRoles, Model.Roles)
}

Here is the view that is referencing _AddUser.cshtml
Users.cshtml:

@model IEnumerable<RobotDog.Models.UserModel>
<table></table>
<div id="addUser">
    @Html.Partial("_AddUser", new ViewDataDictionary())
</div>

Answer 1

The problem with your example is that by calling @Html.Partial you’re rendering the partial _AddUser without ever going through the controller _AddUser method. This means that the Model of the partial view has no Model.Roles to access. You can resolve this a couple of different ways.

One possibility is to use @Html.RenderAction or @Html.Action to call the controller method and let the controller method _AddUser populate the values as you’ve set it up to do.