Well that was certainly interesting. After first confirming the issue with the code you provided, I experimented around and believe I have the root cause. Basically, you are using the same variable name way to often and the model binder appears to be getting confused. You have RecipeId
in your route, RecipeId
in your View Model and RecipeId
as the name of your view bag variable. By altering my variable names, the SelectList
works as expected.
The primary issue is naming your SelectList RecipeId
which matches a property in your model. When you send the new Recipe(), the model binder is attempting to use that value. In your first example, since you have RecipeId
defined in the URL, it is getting it from there. In the second example, there is no RecipeId
to pull from the URL and it is null in the model.
Controller
namespace MvcApplication1.Controllers
{
public class HomeController : Controller
{
private List<Recipe> Recipes;
public HomeController()
{
Recipes = new List<Recipe>
{
new Recipe {RecipeId = 1, RecipeName = "Test - 1"},
new Recipe {RecipeId = 2, RecipeName = "Test - 2"},
new Recipe {RecipeId = 3, RecipeName = "Test - 3"},
};
}
public ActionResult Index(int? id)
{
ViewBag.MyList = new SelectList(Recipes, "RecipeID", "RecipeName", id);
return View(new Recipe());
}
}
}
Index View
@model MvcApplication1.Models.Recipe
@{
ViewBag.Title = "Index";
}
<h2>Index</h2>
@Html.DropDownList("MyRecipeId", (SelectList)ViewBag.MyList)
Basically, vary your parameter names a little bit more to help prevent the model binder from getting confused and/or pulling information from the wrong place.
You can verify this in your second example by sending this in your return statement:
Return View(New Recipe{RecipeId = 3});
The option value with 3 will be selected regardless of what the actual Id sent was.
EDIT
An even better option would be to do what I said to do as an example above. By changing your Action to this:
public ActionResult Index(int? id)
{
ViewBag.MyList = new SelectList(Recipes, "RecipeID", "RecipeName");
return View(new Recipe(RecipeId = id));
}
You can leave your view unchanged. Now, the SelectList will pull from the model that you are sending.