Where should I put this code? - asp.net-mvc

Question

Here's the code, written to be written in a controller:
CategoryRepository categoryRepo = new CategoryRepository();
var categories = categoryRepo.FindAllCategories();
ViewBag.Categories = categories;
Now I'd like to use this to create a nice list of Categories dynamically.
<div id="leftnavigationbar">
<ul>
#foreach (var category in ViewBag.Categories)
{
//Create li here.
}
<!-- ActionLink goes: Text, ActionName, Controller -->
<li>#Html.ActionLink("Libros", "Index", "Home")</li>
<li>#Html.ActionLink("Peliculas, Musica & Juegos", "Index", "Anuncios")</li>
<li>#Html.ActionLink("Computadoras", "Index", "Usuarios")</li>
<li>#Html.ActionLink("Bienes Raices", "Index", "Ayuda")</li>
<li>#Html.ActionLink("Bolsa de Trabajo", "Index", "Contacto")</li>
<li>#Html.ActionLink("Deportes y Fitness", "Index", "Contacto")</li>
<li>#Html.ActionLink("Electronicos y Celulares", "Index", "Contacto")</li>
</ul>
</div>
Right now I'm writing this code to the _Layout.cshtml file. But I'd like to know where to write this so it runs always, sort of like a MasterPage.
Any suggestions?
Edit:
It appears that my initial intent isn't possible.
#foreach (var category in ViewBag.Categories)
{
<li>#Html.ActionLink(category.Name, "Index", "Home")</li>
}
Any suggestions on how accomplish what I'm trying to do? Just pull a list of categories and render them using a foreach loop. Then have it placed somewhere so it's viewable on all pages.

Answer 1

As always you start by creating a view model:
public class CategoryViewModel
{
public string CategoryName { get; set; }
}
Then in your controller you fill the view model:
public ActionResult Index()
{
var categories = categoryRepo.FindAllCategories();
var model = MapModelToViewModel(categories);
return View(model);
}
And finally your strongly typed view could use a display template. Obviously the view will be strongly typed to IEnumerable
<ul>
#Html.EditorForModel()
<!-- ActionLink goes: Text, ActionName, Controller -->
<li>#Html.ActionLink("Libros", "Index", "Home")</li>
...
</ul>
And your display template (~/Views/Home/DisplayTemplates/CategoryViewModel.cshtml):
#model YourApp.Models.CategoryViewModel
<li>#Model.CategoryName</li>
As you can see with strongly typed views and display templates you don't even need to write loops in your views.
As an alternative to display templates you could use Html.Action or Html.RenderAction helers. Phil Haack wrote a nice blog post about them. I suspect that you were forced to use the ugly untyped ViewBag because this code is situated in your master template and you don't have a view model. No problem, with Html.Action you could have a specific controller that will do this:
public class CategoriesController: Controller
{
public ActionResult Index()
{
var categories = categoryRepo.FindAllCategories();
var model = MapModelToViewModel(categories);
return View(model);
}
}
And then have a corresponding partial view which will take care of rendering the categories (~/Views/Categories/Index.cshtml):
#model IEnumerable<YourApp.Models.CategoryViewModel>
#Html.DisplayForModel()
And finally use the same display template.
Now in your master page you could simply include this child action:
<ul>
#Html.Action("index", "categories")
<!-- ActionLink goes: Text, ActionName, Controller -->
<li>#Html.ActionLink("Libros", "Index", "Home")</li>
...
</ul>

Answer 2

You're looking for something called a 'partial view'.