Under-hood explanation required for asp.net MVC tutorial - asp.net-mvc-3

Question

refer to asp.net MVC tutorial:
http://www.asp.net/mvc/tutorials/getting-started-with-aspnet-mvc3/cs/examining-the-edit-methods-and-edit-view
regarding the autogenerated Views\Movies\SearchIndex.cshtml
Question 1:
<p>
#Html.ActionLink("Create New", "Create")
#using (Html.BeginForm())
{
<p>
Genre: #Html.DropDownList("movieGenre", "All")
Title: #Html.TextBox("SearchString", "Movies", FormMethod.Get)
<input type="submit" value="Filter" />
</p>
}
</p>
how does movieGenre refer to #ViewBag.movieGenre, which is obviously defined in Controllers/MoviesController.cs
Question 2:
#foreach (var item in Model) {
<tr>
<td>
#Html.DisplayFor(modelItem => item.Title)
</td>
<td>
#Html.DisplayFor(modelItem => item.ReleaseDate)
</td>
<td>
#Html.DisplayFor(modelItem => item.Genre)
</td>
<td>
#Html.DisplayFor(modelItem => item.Price)
</td>
<td>
#Html.ActionLink("Edit", "Edit", new { id=item.ID }) |
#Html.ActionLink("Details", "Details", new { id=item.ID }) |
#Html.ActionLink("Delete", "Delete", new { id=item.ID })
</td>
</tr>
}
where is modelItem defined? VS2010 shows me modelItem is
IEnumerable <MvcMovie.Model.Movie>
Thanks.

Answer 1

Looks like you've already answered your second question, so I'll just answer your first:
The Html.DropDownList helper will bind itself to ViewData by default if no data is provided to it. ViewBag is simply a dynamic wrapper around the ViewData dictionary, so when you set ViewBag.movieGenre = new SelectList() you are effectively setting ViewData["movieGenre"] = new SelectList().
Now that you have this SelectList in your ViewData, the following will automatically bind this to the dropdown:
#Html.DropDownList("movieGenre")
This implicit binding isn't very well documented. See here for more information:
http://weblogs.asp.net/pjohnson/archive/2012/10/26/mvc-s-html-dropdownlist-and-quot-there-is-no-viewdata-item-of-type-ienumerable-lt-selectlistitem-gt-that-has-the-key.aspx