dropdownlist set selected value in MVC3 Razor

Well its very simple in controller you have somthing like this:

-- Controller

ViewBag.Profile_Id = new SelectList(db.Profiles, "Id", "Name", model.Profile_Id);

--View (Option A)

@Html.DropDownList("Profile_Id")

--View (Option B) --> Send a null value to the list

@Html.DropDownList("Profile_Id", null, "-- Choose --", new {  @class = "input-large" })

just in case someone comes with this question, this is how I do it, please forget about the repository object, I'm using the Repository Pattern, you can use your object context to retrieve the entities. And also don't pay attention to my entity names, my entity type Action has nothing to do with an MVC Action.

Controller:

ViewBag.ActionStatusId = new SelectList(repository.GetAll<ActionStatus>(), "ActionStatusId", "Name", myAction.ActionStatusId);

Pay attention that the last variable of the SelectList constructor is the selected value (object selectedValue)

Then this is my view to render it:

<div class="editor-label">
   @Html.LabelFor(model => model.ActionStatusId, "ActionStatus")
</div>
<div class="editor-field">
   @Html.DropDownList("ActionStatusId")
   @Html.ValidationMessageFor(model => model.ActionStatusId)
</div> 

I think it is pretty simple, I hope this helps! :)

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
)

I drilled down the formation of the drop down list instead of using @Html.DropDownList(). This is useful if you have to set the value of the dropdown list at runtime in razor instead of controller:

<select id="NewsCategoriesID" name="NewsCategoriesID">
    @foreach (SelectListItem option in ViewBag.NewsCategoriesID)
    {
        <option value="@option.Value" @(option.Value == ViewBag.ValueToSet ? "selected='selected'" : "")>@option.Text</option>

    }
</select>