Question

does anyone know how to initialise a MultiSelectList as empty?

I have a ListBoxFor control (MVC3) which i wish the user to populate by using other text and button controls on the web page.

It doesn’t like me commenting out the line below….

many thanks in advance

Items = new MultiSelectList(
    new[] 
    {
        //new { Id = 1, Name = "item 1" }                        
    },
    "Id",
    "Name",
    selectedItemIds
)

Answer 1

When you create a MultiSelectList like that, one of the things the compiler checks is if there are indeed Id and Name fields in the list (IEnumerable) you provided.
The problem with your code is that there are no elements named Id and Name when you send an empty array of anonymous objects, therefore the compiler cannot conclude that this is valid code.

If you want to be able to send an empty array, you will have to refrain from using anonymous types.

Try this:

    public struct myListType
    {
        public int Id;
        public string Name;
    }

Now you can create your MultiSelectList as follows:

Items = new MultiSelectList(
    new List<myListType>(),
    "Id",
    "Name"
);

I left out the selecteditemIDs because there is no use for it when the list is empty, it can only create issues.

Although I am still not certain why you want to do this. I suspect there is a better way, if you can elaborate your intentions.