c# - ASP.NET MVC 使用强类型 ViewModel 将数据从 View 保留到 Controller

Question

对于提出一个之前已经回答过的问题，我提前表示歉意，但我仍然是一个新手，发现很难将解决方案应用于我自己的问题。

我有一个 View 模型，我在创建时填充了一些数据，然后打算使用级联下拉列表填充数据(我不能使用任何客户端脚本)

public class StudentPortalModel
{
    public SelectList LocationListModel { get; set; }
    public SelectList ResidenceListModel { get; set; }
    public int ChosenLocation { get; set; }
    public int ChosenBlock { get; set; }
    public int ChosenFlat { get; set; }
    public int ChosenRoom { get; set; }
    public int ChosenResidence { get; set; }
}

我在 Controller 中有一个操作，它使用一些列表填充 View 模型，我将这些列表用于下拉菜单:

[HttpGet]
        public ActionResult SelectResidence()
        {


            List<Location> objLocationList = (from data in db.Locations select data).ToList();
            SelectList objLocationModelData = new SelectList(objLocationList, "LocationId", "LocationName", 0);


            List<Residence> objResidenceList = (from data in db.Residences select data).ToList();
            SelectList objResidenceModelData = new SelectList(objResidenceList, "ResidenceId", "BlockNumber", 0);


            StudentPortalModel objStudentPortalModel = new StudentPortalModel();
            objStudentPortalModel.LocationListModel = objLocationModelData;
            objStudentPortalModel.ResidenceListModel = objResidenceModelData;


            return View(objStudentPortalModel);
        }

我希望将发送到 View 的模型数据返回给 Controller

 @using (Html.BeginForm("SelectLocation", "StudentPortal", FormMethod.Post))
{
    @Html.DropDownListFor(x => x.ChosenLocation, Model.LocationListModel, "---Select Location---")

    <input type="submit" value="Submit"/>
}

我希望在发送回 HttpGet 方法时保留我发布到 View 的所有数据。

[HttpPost]
        public ActionResult SelectLocation(StudentPortalModel testPortalInstance)
        {
            List<Location> objLocationList = (from data in db.Locations select data).ToList();
            SelectList objLocationModelData = new SelectList(objLocationList, "LocationId", "LocationName", 0);


            List<Residence> objResidenceList = (from data in db.Residences select data).Where(i => i.LocationId == testPortalInstance.ChosenLocation).DistinctBy(x => x.BlockNumber).ToList();
            SelectList objResidenceModelData = new SelectList(objResidenceList, "ResidenceId", "BlockNumber", 0);

            testPortalInstance.LocationListModel = objLocationModelData;
            testPortalInstance.ResidenceListModel = objResidenceModelData;

            return View("SelectResidence", testPortalInstance);

        }

你们可能都知道，唯一被发回的数据是 ChosenLocation，因为当最终用户从下拉列表中选择它时，它被发回，其他一切都是空的

本质上，我需要一种方法来保留用户为每个下拉列表选择的选项。这使我能够缩小用户希望选择的房间的范围，直到我能够从表格中破译一个房间并将其分配给用户。

我最大的问题是我似乎无法找到发送到 View 的 View 模型数据并将其分配给相同的值以发回。当我发回 Controller 时，一切都是空的，这意味着我必须重新创建数据。

我为我的胡言乱语道歉，我把它归结为我只编程了一个月。

提前感谢您的帮助!

Answer 1

不太清楚为什么您不想使用 javascript/jquery(它会提供更好的性能)，但您需要将选定的值从相关的 POST 方法传递给每个 GET 方法。假设第一步是选择一个位置，然后是一个住所，您的 Controller 方法将是

public ActionResult SelectResidence()
{
  List<Location> locations = (from data in db.Locations select data).ToList();
  StudentPortalModel model = new StudentPortalModel()
  {
    LocationListModel = new SelectList(locations, "LocationId", "LocationName")
  }
  return View(model);
}

请注意，为 ResidenceListModel 生成 SelectList 没有意义，因为它不会在第一个 View 中使用

@model StudentPortalModel
@using (Html.BeginForm()) // no need to add parameters
{
  @Html.DropDownListFor(x => x.ChosenLocation, Model.LocationListModel, "---Select Location---")
  <input type="submit" value="Submit"/>
}

将返回到

[HttpPost]
public ActionResult SelectResidence(StudentPortalModel model)
{
  if (!ModelState.IsValid)
  {
    // repopulate locations and return view
  }
  return RedirectToAction("SelectResidence", new { locationID = model.ChosenLocation });
}

将重定向到

public ActionResult SelectResidence(int locationID)
{
  List<Residence> residences = (from data in db.Residences select data).Where(i => i.LocationId == locationID).ToList();
  StudentPortalModel model = new StudentPortalModel()
  {
    ChosenLocation = locationID,
    ResidenceListModel = new SelectList(residences, "ResidenceId", "BlockNumber")
  }
  return View(model);
}

谁的观点

@model StudentPortalModel
@using (Html.BeginForm())
{
  @Html.HiddenFor(x => x.ChosenLocation)
  @Html.DropDownListFor(x => x.ChosenResidence, Model.ResidenceListModel , "---Select Residence---")
  <input type="submit" value="Submit"/>
}

将返回到

public ActionResult SelectResidence(StudentPortalModel model)
{
  if (!ModelState.IsValid)
  {
    // repopulate residences based on the value of model.ChosenLocation and return view
  }
  // your model now contains values for both ChosenLocation and ChosenResidence 
}

类似地，如果您随后需要转到一个 View 以选择一个房间，您将重定向到(例如)public ActionResult SelectResidence(int locationID, int residenceID)