ListBoxFor not letting me select multiple items MVC

Question

When I run the code, I can only select one item at a time, that\'s weird because \'ListBoxFor()\' is used to select multiple items, so what i want is:

Select multipl

Answer 1

You cannot bind a <select multiple> to a collection of complex objects (which is what List<SelectListItem> is). A <select multiple> posts back an array of simple values (in your case, if you select the 1st and 3rd options, it will submit [1, 3] (the values of the selected options).

Your model needs a IEnumerable<int> property to bind to.

public class ModelVariables
{
    public IEnumerable<int> SelectedItems { get; set; }
    public IEnumerable<SelectListItem> DropDownItems { get; set; }
}

and then in the GET method

public ActionResult Index()
{
    var ModelVariables= new ModelVariables()
    {
        DropDownItems = Repository.DDFetchItems(),
        SelectedItems = new List<int>(){ 1, 3 } // to preselect the 1st and 3rd options
    };
    return View(model);
}

and in the view

@Html.ListBoxFor(m => m.SelectedItems, Model.DropDownItems)

Side notes

1. Remove Selected = true in the DDFetchItems() method - its ignored by the ListBoxFor() method because its the value of the property your binding to which determines what is selected
2. There is not need to build a new identical SelectList from the first one inside the ListBoxFor() method (property DropDownItems is already IEumerable<SelectListItem>)