MVC DropDownList SelectedValue无法正确显示

6 回答

• 0

  SelectList 构造函数的最后一个参数（您希望能够传递所选的值id）将被忽略，因为DropDownListFor帮助程序使用您作为第一个参数传递的lambda表达式并使用特定属性的值 .

  所以这是丑陋的方式：

  模型：

  public class MyModel
  {
      public int StatusID { get; set; }
  }
  

  控制器：

  public class HomeController : Controller
  {
      public ActionResult Index()
      {
          // TODO: obviously this comes from your DB,
          // but I hate showing code on SO that people are
          // not able to compile and play with because it has 
          // gazzilion of external dependencies
          var statuses = new SelectList(
              new[] 
              {
                  new { ID = 1, Name = "status 1" },
                  new { ID = 2, Name = "status 2" },
                  new { ID = 3, Name = "status 3" },
                  new { ID = 4, Name = "status 4" },
              }, 
              "ID", 
              "Name"
          );
          ViewBag.Statuses = statuses;
  
          var model = new MyModel();
          model.StatusID = 3; // preselect the element with ID=3 in the list
          return View(model);
      }
  }
  

  视图：

  @model MyModel
  ...    
  @Html.DropDownListFor(model => model.StatusID, (SelectList)ViewBag.Statuses)
  

  ---

  这是正确的方法，使用真实视图模型：

  模型

  public class MyModel
  {
      public int StatusID { get; set; }
      public IEnumerable<SelectListItem> Statuses { get; set; }
  }
  

  控制器：

  public class HomeController : Controller
  {
      public ActionResult Index()
      {
          // TODO: obviously this comes from your DB,
          // but I hate showing code on SO that people are
          // not able to compile and play with because it has 
          // gazzilion of external dependencies
          var statuses = new SelectList(
              new[] 
              {
                  new { ID = 1, Name = "status 1" },
                  new { ID = 2, Name = "status 2" },
                  new { ID = 3, Name = "status 3" },
                  new { ID = 4, Name = "status 4" },
              }, 
              "ID", 
              "Name"
          );
          var model = new MyModel();
          model.Statuses = statuses;
          model.StatusID = 3; // preselect the element with ID=3 in the list
          return View(model);
      }
  }
  

  视图：

  @model MyModel
  ...    
  @Html.DropDownListFor(model => model.StatusID, Model.Statuses)
  

  回复于 2024-05-04T04:16:44+08:00
• -3

  为每个视图创建视图模型 . 这样做只会包含屏幕上所需的内容 . 由于我不知道您在何处使用此代码，因此我们假设您有一个Create视图来添加新订单 .

  为Create视图创建一个新的视图模型：

  public class OrderCreateViewModel
  {
       // Include other properties if needed, these are just for demo purposes
  
       // This is the unique identifier of your order status,
       // i.e. foreign key in your order table
       public int OrderStatusId { get; set; }
       // This is a list of all your order statuses populated from your order status table
       public IEnumerable<OrderStatus> OrderStatuses { get; set; }
  }
  

  订单状态类：

  public class OrderStatus
  {
       public int Id { get; set; }
       public string Name { get; set; }
  }
  

  在“创建”视图中，您将拥有以下内容：

  @model MyProject.ViewModels.OrderCreateViewModel
  
  @using (Html.BeginForm())
  {
       <table>
            <tr>
                 <td><b>Order Status:</b></td>
                 <td>
                      @Html.DropDownListFor(x => x.OrderStatusId,
                           new SelectList(Model.OrderStatuses, "Id", "Name", Model.OrderStatusId),
                           "-- Select --"
                      )
                      @Html.ValidationMessageFor(x => x.OrderStatusId)
                 </td>
            </tr>
       </table>
  
       <!-- Add other HTML controls if required and your submit button -->
  }
  

  您的创建操作方法：

  public ActionResult Create()
  {
       OrderCreateViewModel viewModel = new OrderCreateViewModel
       {
            // Here you do database call to populate your dropdown
            OrderStatuses = orderStatusService.GetAllOrderStatuses()
       };
  
       return View(viewModel);
  }
  
  [HttpPost]
  public ActionResult Create(OrderCreateViewModel viewModel)
  {
       // Check that viewModel is not null
  
       if (!ModelState.IsValid)
       {
            viewModel.OrderStatuses = orderStatusService.GetAllOrderStatuses();
  
            return View(viewModel);
       }
  
       // Mapping
  
       // Insert order into database
  
       // Return the view where you need to be
  }
  

  当您单击提交按钮时，这将保留您的选择，并重定向回创建视图以进行错误处理 .

  我希望这有帮助 .

  回复于 2024-05-04T04:16:44+08:00
• 2

  确保您的返回选择值是一个字符串，而不是在模型中声明它时的int和int .

  例：

  public class MyModel
  {
      public string StatusID { get; set; }
  }
  

  回复于 2024-05-04T04:16:44+08:00
• 46

  对我来说，问题是由大的css填充数字（下拉字段内的顶部和底部填充）引起的 . 基本上，该项目正在显示但不可见，因为它是向下的 . 我通过使填充数字更小来固定它 .

  回复于 2024-05-04T04:16:44+08:00
• 0

  我留下这个，以防它帮助别人 . 我有一个非常相似的问题，没有一个答案有帮助 .

  我的ViewData中有一个属性，其名称与lambda表达式的选择器相同，基本上就像你将 ViewData["StatusId"] 设置为某个东西一样 .

  在我更改了ViewData中匿名属性的名称后，DropDownList帮助程序按预期工作 .

  虽然奇怪 .

  回复于 2024-05-04T04:16:44+08:00
• 1

  请在下面找到示例代码 .

  public class Temp
      {
          public int id { get; set; }
          public string valueString { get; set; }
      }
  

  调节器

  public ActionResult Index()
          {
              // Assuming here that you have written a method which will return the list of Temp objects.
              List<Temp> temps = GetList();
  
              var tempData = new SelectList(temps, "id", "valueString",3);
              ViewBag.Statuses = tempData;
  
              return View();
          }
  

  视图

  @Html.DropDownListFor(model => model.id, (SelectList)ViewBag.Statuses)
      @Html.ValidationMessageFor(model => model.id)
  

  回复于 2024-05-04T04:16:44+08:00