Set the selected item in dropdownlist in MVC3

Question 1

First, create your ViewModel.

public class MovieViewModel
{
    public string Genre { get; set; }

    public IEnumerable<SelectListItem> GenreList
    {
        get
        {
            yield return new SelectListItem { Text = "Comedy", Value = "1" };
            yield return new SelectListItem { Text = "Drama", Value = "2" };
            yield return new SelectListItem { Text = "Documentary", Value = "3" };
        }
    }
}

Then, your controller creates a new instance of this ViewModel and sends it to the view.

public class HomeController : Controller
{
    //
    // GET: /Home/
    public ActionResult Index()
    {
        var viewModel = new MovieViewModel
        {
            Genre = "2"
        };

        return View(viewModel);
    }
}

Finally, the view displays the dropdownlist using the ASP.NET wrapper [Html.DropDownListFor()][1].

@model MvcApplication1.Models.MovieViewModel

<!DOCTYPE html>

<html>
<head>
    <title>My movie</title>
</head>
<body>
    <div>
        @Html.DropDownListFor(m => m.Genre, Model.GenreList)
    </div>
</body>
</html>

The selected value is then automatically chosen according the ViewModel. There's no need to manually set the Selected property of the objects SelectListitem.

Question 2

The SelectListItem type has a Selected property, you need to is to true on the item you wish to set as selected.

You can either set it statically like the following:

public IEnumerable<SelectListItem> GenderList
    {
        get
        {
            [...]
            new SelectListItem { Value = "0", Text = "Select", Selected = true},
            [...]
        }
    }

Or enumerate over the collection for a match with Gender value:

var selected = GenderList.SingleOrDefault(item => item.Text.Equals(this.Gender));
if (selected != null)
    selected.Selected = true;