Null checks in view

Question

It's really a nitty-gritty issue for me, and I have been here many times before. How could this be improved?

I have a basic viewmodel for a view:

public class LoginViewModel : BaseViewModel
{
    public User _User { get; set; }
}

My base class looks like this:

public class BaseViewModel
{
    public List<string> StateMessages { get; set; }
}

The view takes a LoginViewModel, but if I do not pass it in from the controller, then I need to check the StateMessages for null before I access it. So I pass in an empty ViewModel, which is okay, but if I could get around it, it would just look better.

[Route("login")]
[Route( "~/", Name="default" )]
public ActionResult Login()
{
    if (User.Identity.IsAuthenticated)
        return RedirectToAction("Index", "Dashboard");

    return View(new LoginViewModel());
}

Then in the view I don't have check for null, which I prefer:

@foreach (var err in Model.StateMessages)
{
    <span>@err</span><br />
}

I know this is very cosmetic, but is this just they way it should be, or can I somehow avoid to new up a new and empty ViewModel in the controller?

Answer 1

I would suggest changing the type of StateMessages from List<string> to IEnumerable<string>.

It hides implementation details, allowing you flexibility in your choice of data structure in the future.

It also gives you more control over how client code can access/modify the state messages.

Make the backing field readonly to ensure that it's not null.

public class BaseViewModel
{
    private readonly List<string> stateMessages = new List<string>();

    public IEnumerable<string> StateMessages
    {
        get { return this.stateMessage; }
    }

    // Other methods to access/modify stateMessages.
}