asp.net mvc - Binding DropDownList into MVC View

Question

Reading from here: ASP.NET MVC

Action SelectCategory has been created inside controller -

 public ActionResult SelectCategory() {

     List<SelectListItem> items = new List<SelectListItem>();    
     items.Add(new SelectListItem { Text = "Action", Value = "0"});    
     items.Add(new SelectListItem { Text = "Drama", Value = "1" });    
     items.Add(new SelectListItem { Text = "Comedy", Value = "2", Selected = true });    

     ViewBag.MovieType = items;

     return View();    
 }

I am not able to understand binding of Data in following line.

@Html.DropDownList("MovieType")

While binding data in similar way,

@Html.DropDownList("IdList");

I obtain following error-

There is no ViewData item of type 'IEnumerable' that has the key 'IdList'.

Controller Action:

public ActionResult SelectId()
    {
        List<SelectListItem> items = new List<SelectListItem>();
        items.Add(new SelectListItem { Text = "MyId1", Value = "MyId1", Selected=true });
        items.Add(new SelectListItem { Text = "MyId2", Value = "MyId2" });

        ViewBag.IdList = items;
        return View();
    }

What am I missing ? Thank you for your help !

Answer 1

You have set ViewBag.MovieType => when you use @Html.DropDownList("MovieType") the dropdown will use this value. When you write @Html.DropDownList("IdList"), the helper doesn't find a corresponding IdList property in ViewBag and throws an error because it doesn't know from where to bind the data.

Alternatively if you want to change the name of the dropdown you could use the following:

@Html.DropDownList("SelectedMovieType", (IEnumerable<SelectListItem>)ViewBag.MovieType)

and your POST action will have a SelectedMovieType parameter to retrieve the selected value.

But I would avoid ViewBag. Defining a view model is better:

public class MyViewModel
{
    public string SelectedMovieType { get; set; }
    public IEnumerable<SelectListItem> MovieTypes { get; set; }
}

and then have your controller action populate this view model and pass it to the view:

public ActionResult SelectId()
{
    List<SelectListItem> items = new List<SelectListItem>();
    items.Add(new SelectListItem { Text = "MyId1", Value = "MyId1", Selected=true });
    items.Add(new SelectListItem { Text = "MyId2", Value = "MyId2" });

    var model = new MyViewModel
    {
        MovieTypes = items    
    };

    return View(model);
}

and in your strongly typed view:

@model MyViewModel
@Html.DropDownListFor(x => x.SelectedMovieType, Model.MovieTypes)