Passing data from view to method Create in controller [duplicate] - asp.net-mvc

Question

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What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 5 years ago.
I have the following problem with passing data to metod create in controller.
First I display view for method create (GET)
public ActionResult Create(string id)
{
RolesUser RolesUser = new RolesUser(id,repository.GetUserById(id).Roles, repository.GetRoles().ToList());
return View(RolesUser);
}
I use the following ViewModel
public class RolesUser
{
public RolesUser()
{
}
public RolesUser(string id,ICollection<IdentityUserRole> userRoles,List<IdentityRole> Roles)
{
userId = id;
this.Roles = GetNewRolesForUser(userRoles.ToList(), Roles.ToDictionary(x => x.Id, x => x.Name)).ConvertAll(
role =>
{
return new SelectListItem()
{
Text = role.ToString(),
Value = role.ToString(),
Selected = false
};
});
}
public IEnumerable<SelectListItem> Roles { get; set; }
public string userId { get; set; }
private List<string> GetNewRolesForUser(List<IdentityUserRole> UserRoles,Dictionary<string,string> Roles)
{
List<string> AvaiableRoles = new List<string>();
List<string> IdUserRoles = new List<string>();
UserRoles.ForEach(item => IdUserRoles.Add(item.RoleId));
foreach(KeyValuePair<string,string> Role in Roles)
{
if (!IdUserRoles.Contains(Role.Key))
{
AvaiableRoles.Add(Role.Value);
}
}
return AvaiableRoles;
}
}
It displays me essential information on my view in Create.cshtml, when I execute Submit it shows me following error
Object reference not set to an instance of an object.
The metod create (POST) looks like this
[HttpPost]
[ValidateAntiForgeryToken]
[Authorize(Roles ="Admin")]
public ActionResult Create([Bind(Include ="userId")] RolesUser user)
{
if (ModelState.IsValid)
{
try
{
repository.AssignToRole(user.userId, "Klient");
repository.SaveChanges();
}
catch
{
ViewBag.exception = true;
return View();
}
}
ViewBag.exception = false;
return RedirectToAction("Index");
}
Code for Create.cshtml
#model Repository.ViewModels.RolesUser
#{
ViewBag.Title = "Create";
}
<h2>Dodaj poziom dostępu</h2>
#using (Html.BeginForm())
{
#Html.AntiForgeryToken()
<div class="form-horizontal">
<h4>#Model.userId</h4>
<hr />
#Html.ValidationSummary(true, "", new { #class = "text-danger" })
<div class="form-group">
#Html.LabelFor(model => model.userId, htmlAttributes: new { #class = "control-label col-md-2" })
<div class="col-md-10">
#Html.DisplayFor(model => model.userId, new { htmlAttributes = new { #class = "form-control" } })
</div>
</div>
<div class="form-group">
#Html.Label("Poziomy dostępu", htmlAttributes: new { #class = "control-label col-md-2" })
<div class="col-md-10">
#Html.DropDownListFor(m => m.userId, Model.Roles)
</div>
</div>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<input type="submit" value="Dodaj" class="btn btn-default" />
</div>
</div>
</div>
}
It looks like viewmodel is not passing to method, so I have null exception. But I don't understand why, if GET metod render properly view.

Answer 1

The NullReferenceException is likely hit inside the repository.AssignToRole() method because user.userId is null. You should add a hidden input for the userId somewhere inside the form so the userId value is posted to the parameter object on the Create action. If you add it after the #Html.AntiForgeryToken() the start of the form would look like
#using (Html.BeginForm())
{
#Html.AntiForgeryToken()
#Html.HiddenFor(model => model.userId)
...