Question

I am probably doing something silly but cannot find out what. I am trying to modify simple membership functionality in ASP.NET MVC 4. I have slightly modified a RegisterModel coming with the template, and added a list of categories to it like so:

public class RegisterModel
{
    ...

    public List<SelectListItem> Categories { get; set; }
}

Then in the account controller I’m trying to add an item to this list but get “Object reference not set to an instance of an object.” error:

[AllowAnonymous]
public ActionResult Register()
{
    RegisterModel rm = new RegisterModel();

    //SelectListItem guestCategory = new SelectListItem();
    //guestCategory.Value = null;
    //guestCategory.Text = "Guest";

    rm.Categories.Add(new SelectListItem { Value = null, Text = "Guest" });
...

Any ideas why?

Answer 1

you just need to do this before adding items to list , because when you add items its not get instantiated that why its giving error

rm.Categories = new List<SelectListItem>();

that means in this method do like this

[AllowAnonymous]
public ActionResult Register()
{
    RegisterModel rm = new RegisterModel();

    rm.Categories = new List<SelectListItem>();//added line 

    rm.Categories.Add(new SelectListItem { Value = null, Text = "Guest" });
...

or

you can do same thing in constructor of RegisterModel .

public class RegisterModel
{
  public RegisterModel
  {
    Categories = new List<SelectListItem>();//added line 
  }