DropDownListFor setting value of other property when using shared SelectList

Question

I have two dropdowns on my view that share the same SelectList from the model. The problem I have is if a value is selected for "Primary" and not for "Secondary", when load the page with the selected data both "Primary" and "Secondary" will both have the same selected value. If a value for both are selected, then the correct values will be displayed. How can I get it to not show the value for both?

Example Model:

public class ExampleViewModel 
{
     public string Primary { get; set; }
     public string Secondary { get; set; }
     public IEnumerable<string> Categories { get; set; }
}

Example View:

...
@model Categories
...
<div class="form-group">
     @Html.DropDownListFor(x => x.Primary, Model.Categories, "", new { @class = "form-control" })
</div>
<div class="form-group">
     @Html.DropDownListFor(x => x.Secondary, Model.Categories, "", new { @class = "form-control" })
</div>
...

Example Controller:

public ActionResult Index(string primary, string secondary)
{
     return View(new ExampleViewModel {
          Primary = primary,
          Secondary = secondary,
          Categories = context.Query<Categories>().Select(x => new SelectListItem {
               Text = x.Name
           }));
}

Answer 1

As discussed, add new SelectList(Model.Categories),"Value","Text"). Check the syntax for the overload as per comment.

Thanks