ASP.NET MVC Nullreferenceexception: System.Web.Mvc.WebViewPage.Model.get. was null

Question

I'm working on a project (ASP.NET MVC) for school but today I ran into this error. I'm already trying to fix this for a few hours but nothing works. In this application you log in and your profile will load. This works, but as soon as I change the profile data (in a form), post it, and return the view with a refreshed viewmodel (this still works perfectly fine), I get this nullreferenceexception. I've been looking through this exception details but can't figure out whats null, and what's causing this exception.

This is my view:

@model SailyWebApp.Viewmodels.HomeUserViewmodel
@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";
}
<body>
    @if(Session["User"] != null && !string.IsNullOrEmpty(Convert.ToString(Session["User"])))
     {
    <h2>Profile of @Session["User"].ToString()</h2>
    <form runat="server" method="post" id="userdata">
        Name:<br>
        <input type="text" name="Name" value="@Model.user.UserName" required /><br>
        Adress:<br>
        <input type="text" name="Address" value="@Model.user.Adress" required /><br>
        City:<br>
        <input type="text" name="City" value="@Model.user.City" required /><br>
        E-mail:<br>
        <input type="text" name="Mail" value="@Model.user.MailAdress" required /><br>
        Phone number:<br>
        <input type="text" name="Phonenumber" value="@Model.user.PhoneNumber" required /><br>
        Profile description:<br>
        <input type="text" name="Description" value="@Model.user.Description" required /><br>
        <input type="submit" name="Save" value="Save" />
    </form>
    }
    else{
    <p>Please log in</p>
    }
</body>

My HomeController looks like this:

public ActionResult Index()
    {
        if (Session["User"] != null)
        {
            User currentUser = (User)Session["User"];
            HomeUserViewmodel viewmodel = new HomeUserViewmodel();
            viewmodel.user = currentUser;
            return View(viewmodel);
        }

        return View();
    }
    [HttpPost]
    public ActionResult Index(HomeUserViewmodel viewmodel)
    {
        User currentUser = (User)Session["User"];
        if (Logic.UserLogic.EditProfile(viewmodel.Address, viewmodel.City, viewmodel.Mail, viewmodel.Phonenumber, viewmodel.Description, currentUser.UserId))
        {
            currentUser = Logic.UserLogic.LoadUser(currentUser.UserId);
            HomeUserViewmodel newviewmodel = new HomeUserViewmodel();
            viewmodel.user = currentUser;
            Session.Clear();
            Session["User"] = currentUser;
            return View(newviewmodel);
        }
        else
        {
            return View();
        }
    }

My HomeUserViewmodel

public class HomeUserViewmodel
{
    public User user;

    private string name;
    private string address;
    private string city;
    private string mail;
    private string phonenumber;
    private string description;

    public string Name
    {
        get { return name; }
        set { name = value; }
    }
    public string Address
    {
        get { return address; }
        set { address = value; }
    }
    public string City
    {
        get { return city; }
        set { city = value; }
    }
    public string Mail
    {
        get { return mail; }
        set { mail = value; }
    }
    public string Phonenumber
    {
        get { return phonenumber; }
        set { phonenumber = value; }
    }
    public string Description
    {
        get { return description; }
        set { description = value; }
    }
}

Exception details:

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

System.Web.Mvc.WebViewPage.Model.get. was null.

Thanks in advance, I just really don't know where I can find this null value

Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Aleks Andreev, Jan 05 '18 at 15:59
You didn't post the exception details. The exception details will tell you where the null reference occurred. — Robert Harvey, Jan 05 '18 at 16:00
@AleksAndreev I know what a NullRefenceException is, I don't know why I get this one and how to fix it — Thomas van Schijndel, Jan 05 '18 at 16:01
@RobertHarvey I don't exactly know what to copy or where to look in these exception details. I can't find anything odd — Thomas van Schijndel, Jan 05 '18 at 16:05
The stack trace tells you which line of code caused the error. The title of your question is a big clue. — Robert Harvey, Jan 05 '18 at 16:06
FYI, when debugging issues like this in the future a good step is to break-point before the view is returned from the controller and confirm the state of your viewmodel is as expected. — Jonathon Chase, Jan 05 '18 at 16:15
@JonathonChase I always do. I just accidentally swapped the objects in my head. Time to take a break. — Thomas van Schijndel, Jan 05 '18 at 16:18

score 1 · Accepted Answer · answered Jan 05 '18 at 16:05

1

if (Logic.UserLogic.EditProfile(viewmodel.Address, viewmodel.City, viewmodel.Mail, viewmodel.Phonenumber, viewmodel.Description, currentUser.UserId))
{
    currentUser = Logic.UserLogic.LoadUser(currentUser.UserId);
    HomeUserViewmodel newviewmodel = new HomeUserViewmodel();
    viewmodel.user = currentUser; // <- It's right here, this is your problem
    Session.Clear();
    Session["User"] = currentUser;
    return View(newviewmodel);
}

You're populating the user field on the wrong object, the view model you're sending to the view has a null field, and so you are having a null reference exception thrown.

answered Jan 05 '18 at 16:05

Jonathon Chase

9,396
21
39

How did you figure that out without a stack trace? – Robert Harvey Jan 05 '18 at 16:08
His view accesses the ViewModel's user field, and he's not populating it on the action that the exception is thrown in. – Jonathon Chase Jan 05 '18 at 16:09
Seems like he should be writing `newviewmodel.user = currentUser` instead. – Robert Harvey Jan 05 '18 at 16:11
Correct. I think the stack trace would just let us know it was being thrown the first time the user field is being used in the model, which is implied by the error. – Jonathon Chase Jan 05 '18 at 16:12
*facepalm* I did just spend 4 hours on a typo... I indeed populated the wrong viewmodel. Thank you for your help. Totally didn't see this one – Thomas van Schijndel Jan 05 '18 at 16:14

ASP.NET MVC Nullreferenceexception: System.Web.Mvc.WebViewPage.Model.get. was null

1 Answers1