SelectedValues not working in MultiSelectList mvc

I have a class like

 public class Category
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public ICollection<Category> CategorySelected { get; set; }
        public static List<Category> GetOptions()
        {
            var categories = new List<Category>();
            categories.Add(new Category() {  ID = 1, Name = "Bikes" });
            categories.Add(new Category() {  ID = 2, Name = "Cars" });
            categories.Add(new Category() {  ID = 3, Name = "Trucks" });

            return categories;
        }
    }

In the controller I Fill MiltiselectItems and set selectedValues for it

 public ActionResult Index()
    {
       Category cat=new Category();
       cat.CategorySelected.Add(new Category { ID =1, Name = "Bikes" });
       cat.CategorySelected.Add(new Category { ID =3, Name = "Trucks" });

        var list = Category.GetOptions();
        product.Categories = new MultiSelectList(list, "ID", "Name", CategorySelected);
    }

In View Code I have

@Html.ListBox("Category", Model.Categories)

when run my action SelectedValues aren’t working. What I’m doing wrong ?

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

The last parameter of the MultiSelectList constructor takes an array of selected Id‘s not a collection of Category complex types.

If you change it to this instead it will work as expected:

product.Categories = new MultiSelectList(list, "ID", "Name", cat.CategorySelected.Select(c => c.ID).ToArray());

It simply projects it into an array of Id‘s instead.

See below screen shot:

Ps I also had to add this to the constructor of Category to initialize the collection:

public Category()
{
   CategorySelected = new List<Category>();
}

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0