ASP.NEt MVC5--创建下拉列表

Adding Search by Genre

If you added the HttpPost version of the Index  method, delete it now.

Next, you'll add a feature to let users search for movies by genre. Replace  the Index method with the following code:

现在我们来改写Index方法，

   public ActionResult Index(string movieGenre,string searchString)
         {
             var GenreLst = new List<string>();

             var GenreQry = from d in db.Movies
                            orderby d.Genre
                            select d.Genre;
             GenreLst.AddRange(GenreQry.Distinct());
             //SelectList生成列表
             ViewBag.movieGenre = new SelectList(GenreLst);

             //Linq查询
             var movies = from m in db.Movies select m;

             if (!string.IsNullOrEmpty(searchString))
             {
                 movies = movies.Where(s => s.Title.Contains(searchString));
             }
             if (string.IsNullOrEmpty(movieGenre))
             {
                 movies = movies.Where(x => x.Genre == movieGenre);
             }
             return View(movies);

         }

  var GenreQry = from d in db.Movies
                            orderby d.Genre
                            select d.Genre;

当执行完这句代码之后，SQL（GenreQry）为：

 SELECT
 [Extent1].[Genre] AS [Genre]
 FROM [dbo].[Movies] AS [Extent1]
 ORDER BY [Extent1].[Genre] ASC

var movies = from m in db.Movies select m;

执行完这句代码之后，SQL（Movies）为：

 SELECT
 [Extent1].[ID] AS [ID],
 [Extent1].[Title] AS [Title],
 [Extent1].[ReleaseDate] AS [ReleaseDate],
 [Extent1].[Genre] AS [Genre],
 [Extent1].[Price] AS [Price]
 FROM [dbo].[Movies] AS [Extent1]

现在先让我们，在Index视图页面中，添加一个实现下拉框的代码吧：

In the following code:

@Html.DropDownList("movieGenre", "All")
The parameter "movieGenre" provides the key for the DropDownList helper to find a IEnumerable<SelectListItem > in the  ViewBag. The ViewBag was  populated in the action  method:
这句话的意思是：moviegenre参数，为DropDownList方法，提供了主键，去找到在控制器中定义的Viewbag.movieGenre
The parameter "All" provides the item in the list to be preselected. Had we used the following code: 
这句话的意思是：All参数，提供了默认选择项



效果图：


In this section you created a search action method and view that let users search  by movie title and genre. In the next section, you'll look at how to add a  property to the Movie model and how to add an initializer that will  automatically create a test database.

通过下拉列表，来搜索：


通过下拉列表和title输入框搜索：