MVC5 Razor html.dropdownlistfor 当值在数组中时设置选择

我正在使用 C# 和 .NET Framework 4.6.1 开发 ASP.NET MVC 5 应用程序。

我有这个View:

@model MyProject.Web.API.Models.AggregationLevelConfViewModel

[...]

@Html.DropDownListFor(m => m.Configurations[0].HelperCodeType, (SelectList)Model.HelperCodeTypeItems, new { id = "Configurations[0].HelperCodeType" })

The ViewModel is:

public class AggregationLevelConfViewModel
{
    private readonly List<GenericIdNameType> codeTypes;
    private readonly List<GenericIdNameType> helperCodeTypes;

    public IEnumerable<SelectListItem> CodeTypeItems
    {
        get { return new SelectList(codeTypes, "Id", "Name"); }
    }

    public IEnumerable<SelectListItem> HelperCodeTypeItems
    {
        get { return new SelectList(helperCodeTypes, "Id", "Name"); }
    }

    public int ProductionOrderId { get; set; }

    public string ProductionOrderName { get; set; }

    public IList<Models.AggregationLevelConfiguration> Configurations { get; set; }

    public AggregationLevelConfViewModel()
    {
        // Load CodeTypes to show it as a DropDownList
        byte[] values = (byte[])Enum.GetValues(typeof(CodeTypes));

        codeTypes = new List<GenericIdNameType>();
        helperCodeTypes = new List<GenericIdNameType>();

        for (int i = 0; i < values.Length; i++)
        {
            GenericIdNameType cType = new GenericIdNameType()
            {
                Id = values[i].ToString(),
                Name = EnumHelper.GetDescription((CodeTypes)values[i])
            };

            if (((CodeTypes)values[i]) != CodeTypes.NotUsed)
                codeTypes.Add(cType);

            helperCodeTypes.Add(cType);
        }
    }
}

And Models.AggregationLevelConfiguration is:

public class AggregationLevelConfiguration
{
    public byte AggregationLevelConfigurationId { get; set; }
    public int ProductionOrderId { get; set; }
    public string Name { get; set; }
    public byte CodeType { get; set; }
    public byte HelperCodeType { get; set; }
    public int PkgRatio { get; set; }
    public int RemainingCodes { get; set; }
}

我需要在这些属性中设置选定的值：

public IEnumerable<SelectListItem> CodeTypeItems
{
    get { return new SelectList(codeTypes, "Id", "Name"); }
}

public IEnumerable<SelectListItem> HelperCodeTypeItems
{
    get { return new SelectList(helperCodeTypes, "Id", "Name"); }
}

但我无法设置它new SelectList(codeTypes, "Id", "Name"); or new SelectList(helperCodeTypes, "Id", "Name");因为所选值位于Configurations数组：字段AggregationLevelConfiguration.CodeType and AggregationLevelConfiguration.HelperCodeType.

我想我必须在视图中设置选定的值，但我不知道该怎么做。

如何设置选定的值？

很遗憾@Html.DropDownListFor()在循环中渲染控件时，其行为与其他助手略有不同。这之前已被报告为 CodePlex 上的一个问题（不确定这是一个错误还是只是一个限制）

有 2 个选项可以解决此问题，以确保根据模型属性选择正确的选项

Option 1（使用EditorTemplate)

创建自定义EditorTemplate对于集合中的类型。创建一个部分/Views/Shared/EditorTemplates/AggregationLevelConfiguration.cshtml（注意名称必须与类型名称匹配

@model yourAssembly.AggregationLevelConfiguration
@Html.DropDownListFor(m => m.HelperCodeType, (SelectList)ViewData["CodeTypeItems"])
.... // other properties of AggregationLevelConfiguration

然后在主视图中，传递SelectList to the EditorTemplate as additionalViewData

@using (Html.BeginForm())
{
  ...
  @Html.EditorFor(m => m.Configurations , new { CodeTypeItems = Model.CodeTypeItems })
  ...

Option 2（生成一个新的SelectList在每次迭代中并设置selectedValue)

在此选项中您的财产CodeTypeItems应该是IEnumerable<GenericIdNameType>, not a SelectList（或者只是让codeTypes公共财产）。然后在主视图中

@Html.DropDownListFor(m => m.Configurations[0].HelperCodeType, new SelectList(Model.CodeTypeItems, "Id", "Name", Model.Configurations[0].HelperCodeType)

附注：无需使用new { id = "Configurations[0].HelperCodeType" - the DropDownListFor()方法已经生成了id属性