populating a DropDownlist in ASP.NET MVC

Question

I'm learning ASP.NET MVC. I had a small problem when dealing with dropdownlist.

This is what I did in controller

List<Int32> myList = new List<Int32>();
var a = (from m in datacontext.services
                 select m.ServiceID);
myList = a.ToList();
ViewData["ServiceID"] = new SelectList((IEnumerable<SelectListItem>)
                                a.ToList(), "ServiceID", "ServiceID");

In the view

 @Html.DropDownListFor(model => model.ServiceID, ViewData["ServiceID"] as SelectList)

This results in an error

Unable to cast object of type 'System.Collections.Generic.List1[System.Int32]' to type 'System.Collections.Generic.IEnumerable1[System.Web.Mvc.SelectListItem]'."

How can this be resolved?

What's the best way to deal with populating dropdownlist with a query?

Answer 1

There is an error in the cast.

To fix you can do this:

var a = datacontext.services.Select(arg => new { ServiceID = arg.ServiceID }).ToList();
ViewData["ServiceID"] = new SelectList(a, "ServiceID", "ServiceID");

or this:

var a = datacontext.services.Select(arg => arg.ServiceID).ToList();
ViewData["ServiceID"] = new SelectList(a);

In your code a is the list of integers. It cannot be cast into the list of SelectListItem.

Side note: myList variable is not used in your code.

Answer 2

You need to convert your list of Int32's into a List/IEnumerable of SelectListItem's. You are not able to do this as a direct cast (which is what you are trying to do, and what you error represents).

You can adjust your LINQ query to return an IEnumerable<SelectListItem> by changing the select return type.

var a = (from m in datacontext.services
                 select new SelectListItem{ Text = m.ServiceID.ToString(), Value = m.ServiceID.ToString() });

you can then load it into a SelectList via:

ViewData["ServiceID"] = new SelectList(a);

Answer 3

Also, if you have a dropdown list you want populated with text items, you can do the following:

Controller:

public ActionResult Create()
{
    var viewModel = new Store();
    var storeTypes = new SelectList(
                        (   
                            from t in _db.StoreTypes
                            select new SelectListItem
                            {
                                Text  = t.StoreTypeName,
                                Value = SqlFunctions.StringConvert((double)t.StoreTypeID) //convert int to string (yikes)
                            }
                        )
                        , "Value", "Text");

    ViewData["StoreTypes"] = storeTypes;    
     return View(viewModel);
} 

View:

<div class="class">
    <%: Html.DropDownList("StoreTypeID", (SelectList)ViewData["StoreTypes"]) %>
    <%--<%: Html.DisplayTextFor(model => model.StoreTypeID) %>--%>
</div>