Question

I am trying to create a dropdown list to display all the value in a custom collection class
such as

public class MyCustomClassCollection
{

public List<MyCustomClass> {get;set;}

}

I want it to show the Description:string of each MyCustomClass

I tried

<%: Html.DropDownList "Description", MyCustomClass %>

Resharper suggests that I cast MyCustomClass to IEnemerable

but the server returns an unable to cast error.

Any Idea how I can create this DropDownList?

__Modification___

public class ViewModel
    {
        public Detail detail { get; set; }
    }

public class Detail   //Inherited from webservce
{
   public CustomClassCollection {get;set;}
   .... Other Properties, a.k.a Custom Classes
}


public class CustomClassCollection
{
   public List<CustomClass> {get;set;}
}

public class CustomClass {
  public int Id {get;set;}
  public string Description{get;set;}
  ... other properties

}


public ActionResult Index(int? id, DateTime? date)
        {
            if (id.Equals(null))
                id = ######### ;
            if (date.Equals(null))
                date = DateTime.Today;
            var vm = new ViewModel
                         {
                             Detail = _repository.Detail((int)id,(DateTime)date)
                         };
            return View(vm);
        }

Answer 1

The second argument of the DropDownList helper must be an IEnumerable<SelectListItem> or a SelectList which implements this interface for that matter. So in your controller action organize in such a way that you convert your custom collection into an IEnumerable<SelectListItem>. As always you could start by writing a view model:

public class MyViewModel
{
    public string SelectedDescription { get; set; }
    public SelectList Descriptions { get; set; }
}

and then have your controller action query the custom list and populate the view model which will be passed to the view:

public ActionResult Index()
{
    var descriptions = yourCustomCollection.MyCustomClass.Select(x => new
    {
        Value = x.Description,
        Text = x.Description
    });
    var model = new MyViewModel
    {
        Descriptions = new SelectList(descriptions, "Value", "Text")
    };
    return View(model);
}

and finally in your strongly typed view:

<%= Html.DropDownListFor(x => x.SelectedDescription, Model.Decriptions) %>

---

UPDATE:

After posting your updated models (which by the way are still incomplete and impossible to compile as you haven’t provided any property names), here’s an example:

public class ViewModel
{
    public int SelectedId { get; set; }
    public Detail Detail { get; set; }
}

public class Detail
{
   public CustomClassCollection MyCollection { get; set; }
}


public class CustomClassCollection
{
   public List<CustomClass> CustomClass { get; set; }
}

public class CustomClass 
{
    public int Id { get; set; }
    public string Description { get; set; }
}

public class HomeController : Controller
{
    public ActionResult Index()
    {
        var vm = new ViewModel
        {
            Detail = new Detail
            {
                MyCollection = new CustomClassCollection
                {
                    CustomClass = new List<CustomClass>
                    {
                        new CustomClass
                        {
                            Id = 1,
                            Description = "description 1",
                        },
                        new CustomClass
                        {
                            Id = 2,
                            Description = "description 2",
                        },
                        new CustomClass
                        {
                            Id = 3,
                            Description = "description 3",
                        },
                    }
                }
            }
        };
        return View(vm);
    }
}

and in the view:

<%= Html.DropDownListFor(
    x => x.SelectedId, 
    new SelectList(Model.Detail.MyCollection.CustomClass, "Id", "Description")
) %>

What you have to understand in order to define a dropdown list in ASP.NET MVC ius that you need 2 things:

1. A scalar property to bind the selected value to (SelectedId in my example)
2. A collection to bind the list to (Model.Detail.MyCollection.CustomClass in the example)