Set the first item's value in DDL (MVC4) to null - asp.net-mvc

Question

I have a DDL in my view and i read items and values of this DDL from DB like this :
ViewBag.ContentGroup = new SelectList(obj.GetContentGrouplist(), "Id", "Name");
I put it in viewbag and i read the viewbag from the view like this :
<div class="editor-label">
#Html.LabelFor(model => model.ContentGroupFKId)
</div>
<div class="editor-field">
#Html.DropDownListFor(x => x.ContentGroupFKId, (SelectList)ViewBag.ContentGroup)
#Html.ValidationMessageFor(model => model.ContentGroupFKId)
</div>
So i need a DDL that the first item of that be null how can i do that?
I tried this but it doesn't work:
#Html.DropDownListFor(x => x.ContentGroupFKId,new SelectList(new List<Object> {new {value = null, text = "Select"} (SelectList)ViewBag.ContentGroup)
Best regards.

Answer 1

I don't think you can. Whatever value you provide is going to be used to generate html in the form of a select list, which doesn't support null. As long as you have a DropDownListFor, it is going to set a value, even if it is empty. The best thing you can do is make the first value a "Please select an item" option and set it to null server side.
There isn't a great way to add the "Please Select" option (at least none that I have seen. People are welcome to correct me though!), but there are a few ways to do it. One would be to create a dummy content group that just has a name and id.
var contentGroups = obj.GetContentGrouplist();
contentGroups.Insert(0, new ContentGroup{Id = "0", Name = "Please select a content group"};
ViewBag.ContentGroup = new SelectList(contentGroups, "Id", "Name");
Or you can create an object (which you would use anywhere you needed this functionality) that just holds a text and value property and then manually add all of your content groups to it, including the empty one.
class DropDownListOption{
public string Text{get;set;}
public string Value{get;set;}
}
then in your code
var contentGroups = obj.GetContentGrouplist();
var options = new List<DropDownListOption>();
options.Add(new DropDownListOption{ Id = "0", Text = "Please select a content group"};
foreach(var group in contentGroups)
{
options.Add(new DropDownListOption{ Id = group.Id, Text = group.Name};
}
ViewBag.ContentGroup = new SelectList(options, "Id", "Name");
Both of these options will work. I like the second option better because you can create a generic method of handling all drop down lists a certain way. You will have to handle ContentGroups with an ID of 0 as being null when the user submits the form, but at least it is a way of tracking it.
If I think of another way ill add it.