Question

我想问一个非常简单的问题，即我正在创建一个简单的MVC应用程序来测试下拉功能，控制器中有2个操作方法，一个用于GET，另一个用于POST。我想使用HTML表单助手回发从下拉列表中获取所选值。这是我的M，V和C;

型号：

public class Programming
      {
           public int selectedId { get; set; }

            public List<SelectListItem> languanges;
      }

控制器：

public class HomeController : Controller
 {
   private Programming programming;
   private List<SelectListItem> list;

   public HomeController()
     {
        programming = new Programming();
        programming.languanges = new List<SelectListItem>();


        list = new List<SelectListItem>() {
        new SelectListItem(){ Value="1", Text="ActionScript"},
        new SelectListItem(){ Value="2", Text="AppleScript"},
        new SelectListItem(){ Value="3", Text="Asp"},
        new SelectListItem(){ Value="4", Text="BASIC"},
        new SelectListItem(){ Value="5", Text="C"},
        new SelectListItem(){ Value="6", Text="C++"},
        new SelectListItem(){ Value="7", Text="Clojure"},
        new SelectListItem(){ Value="8", Text="COBOL"},
        new SelectListItem(){ Value="9", Text="ColdFusion"},
        new SelectListItem(){ Value="10", Text="Erlang"},
        new SelectListItem(){ Value="11", Text="Fortran"},
        new SelectListItem(){ Value="12", Text="Groovy"},
        new SelectListItem(){ Value="13", Text="Haskell"}, 
        new SelectListItem(){ Value="14", Text="instinctcoder.com"},
        new SelectListItem(){ Value="15", Text="Java"},
        new SelectListItem(){ Value="16", Text="JavaScript"},
        new SelectListItem(){ Value="17", Text="Lisp"},
        new SelectListItem(){ Value="18", Text="Perl"},
        new SelectListItem(){ Value="19", Text="PHP"},
        new SelectListItem(){ Value="20", Text="Python"},
        new SelectListItem(){ Value="21", Text="Ruby"},
        new SelectListItem(){ Value="22", Text="Scala"},
        new SelectListItem(){ Value="23", Text="Scheme"},
        };
      }
        // GET: Home
        public ActionResult Index()
        {
            programming.languanges = list;

            return View(programming);
        }

        [HttpPost]
        public ActionResult Index(Programming programming)`enter code here`
        {
            return View();
        }

}

查看：

        @model BSTNTest.Models.Programming

        @{
            ViewBag.Title = "Index";
          }

        @using (Html.BeginForm("Index", "Home", FormMethod.Post))
        {
            @Html.DropDownListFor(c => c.selectedId, Model.languanges)
            <button type="submit" class="btn btn-primary">Submit</button>
        }

如果我在post动作中设置断点，我会将语言设为null！为什么会这样？

最后以null异常结束。

由于

Answer 1

你必须在构造函数中将List不在Index方法中，而是在它的创建位置：

   public HomeController()
     {
        programming = new Programming();
        programming.languanges = new List<SelectListItem>();


        list = new List<SelectListItem>() {
        new SelectListItem(){ Value="1", Text="ActionScript"},
        new SelectListItem(){ Value="2", Text="AppleScript"},
        new SelectListItem(){ Value="3", Text="Asp"},
        new SelectListItem(){ Value="4", Text="BASIC"},
        new SelectListItem(){ Value="5", Text="C"},
        new SelectListItem(){ Value="6", Text="C++"},
        new SelectListItem(){ Value="7", Text="Clojure"},
        new SelectListItem(){ Value="8", Text="COBOL"},
        new SelectListItem(){ Value="9", Text="ColdFusion"},
        new SelectListItem(){ Value="10", Text="Erlang"},
        new SelectListItem(){ Value="11", Text="Fortran"},
        new SelectListItem(){ Value="12", Text="Groovy"},
        new SelectListItem(){ Value="13", Text="Haskell"}, 
        new SelectListItem(){ Value="14", Text="instinctcoder.com"},
        new SelectListItem(){ Value="15", Text="Java"},
        new SelectListItem(){ Value="16", Text="JavaScript"},
        new SelectListItem(){ Value="17", Text="Lisp"},
        new SelectListItem(){ Value="18", Text="Perl"},
        new SelectListItem(){ Value="19", Text="PHP"},
        new SelectListItem(){ Value="20", Text="Python"},
        new SelectListItem(){ Value="21", Text="Ruby"},
        new SelectListItem(){ Value="22", Text="Scala"},
        new SelectListItem(){ Value="23", Text="Scheme"},
        };
        programming.languanges = list;
      }

请注意：你的post方法参数与全局变量同名，所以你要隐藏它。在Post方法中，您应该返回带有模型的视图以将列表放在那里。

[HttpPost]
public ActionResult Index(Programming par)
{
    return View(programming);
}

ASP.NET MVC DropDownListFor在回发时返回null

1 个答案: