Question

Here is my model:

public class NewsCategoriesModel {
    public int NewsCategoriesID { get; set; }        
    public string NewsCategoriesName { get; set; }
}

My controller:

public ActionResult NewsEdit(int ID, dms_New dsn) {
    dsn = (from a in dc.dms_News where a.NewsID == ID select a).FirstOrDefault();
    var categories = (from b in dc.dms_NewsCategories select b).ToList();
    var selectedValue = dsn.NewsCategoriesID;
    SelectList ListCategories = new SelectList(categories, "NewsCategoriesID", "NewsCategoriesName",selectedValue);

    // ViewBag.NewsCategoriesID = new SelectList(categories as IEnumerable<dms_NewsCategory>, "NewsCategoriesID", "NewsCategoriesName", dsn.NewsCategoriesID);
    ViewBag.NewsCategoriesID = ListCategories;
    return View(dsn);
}

And then my view:

@Html.DropDownList("NewsCategoriesID", (SelectList)ViewBag.NewsCategoriesID)

When i run, the DropDownList does not select the value I set.. It is always selecting the first option.

Answer 1

You should use view models and forget about ViewBag Think of it as if it didn’t exist. You will see how easier things will become. So define a view model:

public class MyViewModel
{
    public int SelectedCategoryId { get; set; }
    public IEnumerable<SelectListItem> Categories { get; set; } 
}

and then populate this view model from the controller:

public ActionResult NewsEdit(int ID, dms_New dsn)
{
    var dsn = (from a in dc.dms_News where a.NewsID == ID select a).FirstOrDefault();
    var categories = (from b in dc.dms_NewsCategories select b).ToList();

    var model = new MyViewModel
    {
        SelectedCategoryId = dsn.NewsCategoriesID,
        Categories = categories.Select(x => new SelectListItem
        {
            Value = x.NewsCategoriesID.ToString(),
            Text = x.NewsCategoriesName
        })
    };
    return View(model);
}

and finally in your view use the strongly typed DropDownListFor helper:

@model MyViewModel

@Html.DropDownListFor(
    x => x.SelectedCategoryId,
    Model.Categories
)