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：