MVC SelectList Drop down default - model-view-controller

Question

In the SelectList drop down, I like if the Count is 1, I like to default the value of what is there in the drugfamilylist which in this case is just 1 value. I cannot figure out how to do this.
I had the following below:
var drugfamilylist = (from dt in DataContext.Drugs
select dt.Drugvalue).Distinct().ToList();
if (drugfamilylist.Count == 1)
{
ViewBag.DrugFamily = new SelectList(drugfamilylist);
}
I tried but that idd not work either :
var drugfamilylist = (from dt in DataContext.Drugs
select dt.Drugvalue).Distinct().ToList();
if (drugfamilylist.Count == 1)
{
ViewBag.DrugFamily = new SelectList(drugfamilylist,drugfamilylist);
}

Answer 1

Typically I would have View strongly-typed to a ViewModel. The ViewModel would contain both the list of available items and the corresponding value of the currently selected element.
public class MyViewModel
{
public IList<string> DrugFamilyList;
public string SelectedDrugFamily;
}
In the controller you could then populate both the list of available items and the Selected items when the list of available items was a single element.
public ActionResult MyAction()
{
var vm = new MyViewModel();
vm.DrugFamilyList = (from dt in DataContext.Drugs
select dt.Drugvalue).Distinct().ToList();
vm.SelectedDrugFamily = (vm.DrugFamilyList.Count==1) ?
vm.DrugFamilyList[0] : null;
return View(vm);
}
And then use the HtmlHelper to build the select box:
#Html.DropDownListFor(m => m.SelectedDrugFamily, new SelectList(Model.DrugFamilyList, Model.SelectedDrugFamily))
However, if you didn't want to use the recommended ViewModel pattern, you could always accomplish the same thing with ViewBag.
ViewBag.DrugFamilyList = (from dt in DataContext.Drugs
select dt.Drugvalue).Distinct().ToList();
ViewBag.SelectedDrugFamily = (ViewBag.DrugFamilyList.Count==1) ?
ViewBag.DrugFamilyList[0] : null;
And then in the View use a similar helper:
#Html.DropDownList("desiredfieldname", new SelectList(ViewBag.DrugFamilyList, "", "", ViewBag.SelectedDrugFamily ))
This was written free-hand and not tested. I hope it helps.