如何让我的MultiSelectList绑定到我的数据模型？

Question

我和汽车之间有许多关系.在我看来,我希望能够为灯光等项目提供多选列表.我尝试了很多不同的格式,我似乎无法获得列表来设置所选项目.我喜欢的方法是@Html.ListBoxFor(model => model.enitity.relatedentity,Model.SomeSelectListItemList),但是我似乎无法获取列表以在视图中设置所选项目.

下面是我测试的代码,我使用的是Asp.net MVC5,C#和实体框架6.

这是我的控制器动作

    // GET: Car/Edit/
    [Authorize(Roles = "Ecar")]
    public ActionResult Edit(int id)
    {


        CarsEditViewModel carEditViewModel = new CarsEditViewModel();

        carEditViewModel.Cars = unitOfWorkcar.CarRepository.FindIncluding(id);

        IList<Approval> approvalList = unitOfWorkcar.ApprovalRepository.All.ToList();
        IList<Connector> connectorList = unitOfWorkcar.ConnectorRepository.All.ToList();
        IList<InputVoltage> inputVoltagesList = unitOfWorkcar.InputVoltageRepository.All.ToList();



        carEditViewModel.ApprovalList = from c in approvalList select new SelectListItem { Text = c.Name, Value = c.Id.ToString(), Selected = true};

        carEditViewModel.Categories = new MultiSelectList(carEditViewModel.ApprovalList, "Value", "Text", "Selected");


       // ,carEditViewModel.ApprovalList.Select(c => c.Text),carEditViewModel.ApprovalList.Select(c => c.Selected)

        //carEditViewModel.ApprovalList = from c in approvalList select new MultiSelectList( //{ Selected = (carEditViewModel.Cars.Approvals.Any(app => app.Id == c.Id)) , Text = c.Name, Value = c.Id.ToString() };
       // carEditViewModel.ConnectorList = from c in connectorList select new SelectListItem { Selected = true,  Text = c.Name, Value = c.Id.ToString() };
        carEditViewModel.InputVoltageList = from c in inputVoltagesList select new SelectListItem { Text = c.Name, Value = c.Id.ToString() };



        return View(carEditViewModel);

    }

这是我的看法

@model NewBobPortal.ViewModels.CarsEditViewModel

 @using (Html.BeginForm())
{



   @* @Html.ListBoxFor("SelectedApprovals",model => model., new { @class = "multiselect" })*@
    @*@Html.ListBoxFor(model => model.Cars.Approvals, Model.ApprovalList)
    @Html.ListBoxFor(model => model.Cars.Connectors,Model.ConnectorList, new {Multiple = "multiple"})
    @Html.ListBoxFor(model => model.ConnectorList, Model.ConnectorList)*@
    @*@Html.ListBox("test",Model.Cars.InputVoltages, Model.InputVoltageList)*@
    @Html.DropDownList("somethingelse", new MultiSelectList(Model.InputVoltageList, "Value", "Text", Model.InputVoltageList.Select(c => c.Value)), new { multiple = "multiple" })
    @Html.DropDownListFor(model => model.Cars.InputVoltages , new MultiSelectList(Model.LensColorList, "Value", "Text", Model.LensColorList.Select(c => c.Value)), new { multiple = "multiple" })


    @Html.ListBoxFor(m => m.Cars.Approvals, Model.Categories)



    <p>
        <input type="submit" value="Save" />
    </p>

}

这是我的viewmodel

using NewBobPortal.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

 namespace NewBobPortal.ViewModels
 {
public class CarsEditViewModel
{
    public Car Cars { get; set; }
    public IEnumerable<SelectListItem> ApprovalList { get; set; }
    public IEnumerable<MultiSelectList> ConnectorList { get; set; }
    public IEnumerable<SelectListItem> InputVoltageList { get; set; }




    public MultiSelectList Categories { get; set; }
    public IEnumerable<Approval> SelectedCategories { get; set; }

}

}

Answer 1

发布多对多关系的值的最大问题是在模型上没有要绑定的直接字段.这就是视图模型变得非常方便的地方,您已经在使用它,但不是以正确的方式.

首先,你需要你的SelectList,实际上只是一个IEnumerable<SelectListItem>.这将包含所有可用选项,这很容易.所以在你的视图模型中:

public IEnumerable<SelectListItem> CategoryChoices { get; set; }

在你的行动中:

carEditViewModel.CategoryChoices = approvalList.Select(m => new SelectListItem {
    Text = c.Name,
    Value = c.Id.ToString()
});

请注意,我没有设置Selected:我们将让HtmlHelper处理它.我也没有处理MultiSelectList过.

现在,您还需要回复一些内容,因为您的值将是ID,我们将使用a List<int>,因此在您的视图模型中:

private List<int> selectedCategories;
public List<int> SelectedCategories
{
    get
    {
        if (selectCategories == null)
        {
            selectedCategories = Categories.Select(m => m.Id).ToList();
        }
        return selectedCategories;
    }
    set { selectedCategories = value; }
}

这里有一点点.set属性的方法很简单:当我们返回一个已发布的值时,只需设置selectedCategories为该值即可.这get有点复杂:在这里我们需要压缩你的类别对象列表(Categories这里称为因为我不知道它实际来自哪里)到这些类别的id的简单列表中.

现在,在您看来:

@Html.ListBoxFor(m => m.SelectedCategories, Model.CategoryChoices)

这就是你所需要的.您正在使用ListBox控件,因此它已经是一个多选列表.并且,通过将其绑定到所有当前选定的ID的列表,它知道在SelectListItem其获取的列表中自动选择哪些项目Model.CategoryChoices.

在您的帖子操作中,您需要将这些ID转换为其关联的对象:

 var newCategories = repository.Categories.Where(m => carEditViewModel.SelectedCategories.Contains(m.Id));

然后,您可以手动将模型的类别设置为此新列表:

car.Categories = newCategories;