In my controller I have this:

ViewData["maskList"] = new SelectList(equipmentRepository.GetMasks(), "Id", "DisplayName");

and then I bind it to my view using

<div each="var nfa in mfa.NasalFittingAssessment">
    ${Html.DropDownList("NasalMaskTypeId", ViewData["maskList"] as IEnumerable<System.Web.Mvc.SelectListItem>, new { class = "ddl" })}                
</div>

Note that I'm using the spark view engine so this DropDownList is getting rendered to the page via a loop. This means that the selected value of the dropdown list will change on each iteration of the loop.

What I can't work out is how to pass in the value I want to set the DropDownList to based on the value that is currently being rendered to the screen.