What is the best way to access a model from a view when the model is optional? - asp.net-mvc-3

Question

I have a single view that is used by two Controller Actions.
My Controller:
AccountController {
...
ActionResult LogOn() {
return View()
}
[HttpPost]
ActionResult LogOn(LogOnModel model) {
return View(model)
}
}
My View:
<% if (!String.IsNullOrEmpty(Model.UserName)) { %>
<div class="username"><% Response.Write(Model.UserName); %></div>
<% } %>
Of course, the problem with the above code is that I get an error "Object Reference not set to an instance of an object" on the line that references Model.UserName.
What is the best way to my view to support both Actions? I can replace the HttpGet LogOn method with:
ActionResult LogOn() {
result View(new LogOnModel());
}
That works, but it doesn't seem very elegant and I'm sure an empty model will break some more complex models that I will need to create later on. Is there a better way? Thanks!

Answer 1

What is the best way to my view to support both Actions?
If a view is strongly typed to a view model (which is what absolutely all your views should be) you should make sure that all your controller actions serving those views (which is pretty much all your controller actions in your application) are passing a view model to those views.
Which is pretty much bla-bla which translated into source code pretty basically means this:
ActionResult LogOn() {
return View(new LogOnModel())
}
That works, but it doesn't seem very elegant and I'm sure an empty
model will break some more complex models that I will need to create
later on.
That's the correct way. Don't worry. You ain't gonna break anything. It's by not providing a view model to your views that you are breaking stuff.
Also as a side note you should absolutely never use Response.Write in a view. So instead of:
<% Response.Write(Model.UserName); %>
you totally want:
<%= Html.DisplayFor(x => x.UserName) %>
or:
<%: Model.UserName %>
but personally I prefer the DisplayFor helper since it will take care of any metadata.

Answer 2

You can either return a different view or as you have done, return a new model.

Answer 3

As noted by other commenters, your Controller should support the strong-typeness of your view. But if you insist on proceeding with the anti-pattern. Replace this:
<% if (!String.IsNullOrEmpty(Model.UserName)) { %>
<div class="username"><% Response.Write(Model.UserName); %></div>
<% } %>
with this:
<% if (Model!= null && !String.IsNullOrEmpty(Model.UserName)) { %>
<div class="username"><% Response.Write(Model.UserName); %></div>
<% } %>