Unterstützung für optgroup in dropdownlist .NET MVC?

Meine Erweiterung ist ein bisschen komplizierter, aber es hat alle überladungen als original DropDownList hat.

Eigentlich habe ich es extra produzieren zu können DropDownList mit Gruppen und verwandelte in zwei verbundene wählt mit Hilfe von jDoubleSelect

using System;using System.Collections;using System.Collections.Generic;using System.Globalization; using System.Linq;using System.Linq.Expressions;using System.Text; using System.Web;using System.Web.Mvc;using System.Web.Routing;

public class GroupedSelectListItem : SelectListItem
{
    public string GroupKey { get; set; }
    public string GroupName { get; set; }
}

public static class HtmlHelpers
{
    public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name)
    {
        return DropDownListHelper(htmlHelper, name, null, null, null);
    }

    public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable<GroupedSelectListItem> selectList)
    {
        return DropDownListHelper(htmlHelper, name, selectList, null, null);
    }

    public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, string optionLabel)
    {
        return DropDownListHelper(htmlHelper, name, null, optionLabel, null);
    }

    public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable<GroupedSelectListItem> selectList, IDictionary<string, object> htmlAttributes)
    {
        return DropDownListHelper(htmlHelper, name, selectList, null, htmlAttributes);
    }

    public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable<GroupedSelectListItem> selectList, object htmlAttributes)
    {
        return DropDownListHelper(htmlHelper, name, selectList, null, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
    }

    public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable<GroupedSelectListItem> selectList, string optionLabel)
    {
        return DropDownListHelper(htmlHelper, name, selectList, optionLabel, null);
    }

    public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable<GroupedSelectListItem> selectList, string optionLabel, IDictionary<string, object> htmlAttributes)
    {
        return DropDownListHelper(htmlHelper, name, selectList, optionLabel, htmlAttributes);
    }

    public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable<GroupedSelectListItem> selectList, string optionLabel, object htmlAttributes)
    {
        return DropDownListHelper(htmlHelper, name, selectList, optionLabel, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
    }

    public static MvcHtmlString DropDownGroupListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<GroupedSelectListItem> selectList)
    {
        return DropDownGroupListFor(htmlHelper, expression, selectList, null /* optionLabel */, null /* htmlAttributes */);
    }

    public static MvcHtmlString DropDownGroupListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<GroupedSelectListItem> selectList, object htmlAttributes)
    {
        return DropDownGroupListFor(htmlHelper, expression, selectList, null /* optionLabel */, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
    }

    public static MvcHtmlString DropDownGroupListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<GroupedSelectListItem> selectList, IDictionary<string, object> htmlAttributes)
    {
        return DropDownGroupListFor(htmlHelper, expression, selectList, null /* optionLabel */, htmlAttributes);
    }

    public static MvcHtmlString DropDownGroupListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<GroupedSelectListItem> selectList, string optionLabel)
    {
        return DropDownGroupListFor(htmlHelper, expression, selectList, optionLabel, null /* htmlAttributes */);
    }

    public static MvcHtmlString DropDownGroupListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<GroupedSelectListItem> selectList, string optionLabel, object htmlAttributes)
    {
        return DropDownGroupListFor(htmlHelper, expression, selectList, optionLabel, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
    }

    public static MvcHtmlString DropDownGroupListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<GroupedSelectListItem> selectList, string optionLabel, IDictionary<string, object> htmlAttributes)
    {
        if (expression == null)
        {
            throw new ArgumentNullException("expression");
        }

        return DropDownListHelper(htmlHelper, ExpressionHelper.GetExpressionText(expression), selectList, optionLabel, htmlAttributes);
    }

    private static MvcHtmlString DropDownListHelper(HtmlHelper htmlHelper, string expression, IEnumerable<GroupedSelectListItem> selectList, string optionLabel, IDictionary<string, object> htmlAttributes)
    {
        return SelectInternal(htmlHelper, optionLabel, expression, selectList, false /* allowMultiple */, htmlAttributes);
    }


    //Helper methods

    private static IEnumerable<GroupedSelectListItem> GetSelectData(this HtmlHelper htmlHelper, string name)
    {
        object o = null;
        if (htmlHelper.ViewData != null)
        {
            o = htmlHelper.ViewData.Eval(name);
        }
        if (o == null)
        {
            throw new InvalidOperationException(
                String.Format(
                    CultureInfo.CurrentCulture,
                    "Missing Select Data"));
        }
        var selectList = o as IEnumerable<GroupedSelectListItem>;
        if (selectList == null)
        {
            throw new InvalidOperationException(
                String.Format(
                    CultureInfo.CurrentCulture,
                    "Wrong Select DataType"));
        }
        return selectList;
    }

    internal static string ListItemToOption(GroupedSelectListItem item)
    {
        var builder = new TagBuilder("option")
        {
            InnerHtml = HttpUtility.HtmlEncode(item.Text)
        };
        if (item.Value != null)
        {
            builder.Attributes["value"] = item.Value;
        }
        if (item.Selected)
        {
            builder.Attributes["selected"] = "selected";
        }
        return builder.ToString(TagRenderMode.Normal);
    }

    private static MvcHtmlString SelectInternal(this HtmlHelper htmlHelper, string optionLabel, string name, IEnumerable<GroupedSelectListItem> selectList, bool allowMultiple, IDictionary<string, object> htmlAttributes)
    {
        name = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
        if (String.IsNullOrEmpty(name))
        {
            throw new ArgumentException("Null Or Empty", "name");
        }

        bool usedViewData = false;

        //If we got a null selectList, try to use ViewData to get the list of items.
        if (selectList == null)
        {
            selectList = htmlHelper.GetSelectData(name);
            usedViewData = true;
        }

        object defaultValue = (allowMultiple) ? htmlHelper.GetModelStateValue(name, typeof(string[])) : htmlHelper.GetModelStateValue(name, typeof(string));

        //If we haven't already used ViewData to get the entire list of items then we need to
        //use the ViewData-supplied value before using the parameter-supplied value.
        if (!usedViewData)
        {
            if (defaultValue == null)
            {
                defaultValue = htmlHelper.ViewData.Eval(name);
            }
        }

        if (defaultValue != null)
        {
            var defaultValues = (allowMultiple) ? defaultValue as IEnumerable : new[] { defaultValue };
            var values = from object value in defaultValues select Convert.ToString(value, CultureInfo.CurrentCulture);
            var selectedValues = new HashSet<string>(values, StringComparer.OrdinalIgnoreCase);
            var newSelectList = new List<GroupedSelectListItem>();

            foreach (var item in selectList)
            {
                item.Selected = (item.Value != null) ? selectedValues.Contains(item.Value) : selectedValues.Contains(item.Text);
                newSelectList.Add(item);
            }
            selectList = newSelectList;
        }

        //Convert each ListItem to an <option> tag
        var listItemBuilder = new StringBuilder();

        //Make optionLabel the first item that gets rendered.
        if (optionLabel != null)
        {
            listItemBuilder.AppendLine(ListItemToOption(new GroupedSelectListItem { Text = optionLabel, Value = String.Empty, Selected = false }));
        }

        foreach (var group in selectList.GroupBy(i => i.GroupKey))
        {
            string groupName = selectList.Where(i => i.GroupKey == group.Key).Select(it => it.GroupName).FirstOrDefault();
            listItemBuilder.AppendLine(string.Format("<optgroup label=\"{0}\" value=\"{1}\">", groupName, group.Key));
            foreach (GroupedSelectListItem item in group)
            {
                listItemBuilder.AppendLine(ListItemToOption(item));
            }
            listItemBuilder.AppendLine("</optgroup>");
        }

        var tagBuilder = new TagBuilder("select")
        {
            InnerHtml = listItemBuilder.ToString()
        };
        tagBuilder.MergeAttributes(htmlAttributes);
        tagBuilder.MergeAttribute("name", name, true /* replaceExisting */);
        tagBuilder.GenerateId(name);
        if (allowMultiple)
        {
            tagBuilder.MergeAttribute("multiple", "multiple");
        }

        //If there are any errors for a named field, we add the css attribute.
        ModelState modelState;
        if (htmlHelper.ViewData.ModelState.TryGetValue(name, out modelState))
        {
            if (modelState.Errors.Count > 0)
            {
                tagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName);
            }
        }

        return MvcHtmlString.Create(tagBuilder.ToString());
    }

    internal static object GetModelStateValue(this HtmlHelper helper, string key, Type destinationType)
    {
        ModelState modelState;
        if (helper.ViewData.ModelState.TryGetValue(key, out modelState))
        {
            if (modelState.Value != null)
            {
                return modelState.Value.ConvertTo(destinationType, null /* culture */);
            }
        }
        return null;
    }

}

InformationsquelleAutor der Antwort Serge Zab

Schreibe ich gerade eine Erweiterungen für hierzu finden Sie unter:

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web.Routing;

namespace System.Web.Mvc.Html
{
    public static class GroupDropListExtensions
    {
        public static string GroupDropList(this HtmlHelper helper, string name, IEnumerable<GroupDropListItem> data, string SelectedValue, object htmlAttributes)
        {
            if (data == null && helper.ViewData != null)
                data = helper.ViewData.Eval(name) as IEnumerable<GroupDropListItem>;
            if (data == null) return string.Empty;

            var select = new TagBuilder("select");

            if (htmlAttributes != null)
                select.MergeAttributes(new RouteValueDictionary(htmlAttributes));

            select.GenerateId(name);

            var optgroupHtml = new StringBuilder();
            var groups = data.ToList();
            foreach (var group in data)
            {
                var groupTag = new TagBuilder("optgroup");
                groupTag.Attributes.Add("label", helper.Encode( group.Name));
                var optHtml = new StringBuilder();
                foreach (var item in group.Items)
                {
                    var option = new TagBuilder("option");
                    option.Attributes.Add("value", helper.Encode(item.Value));
                    if (SelectedValue != null && item.Value == SelectedValue)
                        option.Attributes.Add("selected", "selected");
                    option.InnerHtml = helper.Encode(item.Text);
                    optHtml.AppendLine(option.ToString(TagRenderMode.Normal));
                }
                groupTag.InnerHtml = optHtml.ToString();
                optgroupHtml.AppendLine(groupTag.ToString(TagRenderMode.Normal));
            }
            select.InnerHtml = optgroupHtml.ToString();
            return select.ToString(TagRenderMode.Normal);
        }
}

    public class GroupDropListItem
    {
        public string Name { get; set; }
        public List<OptionItem> Items { get; set; }
    }

    public class OptionItem
    {
        public string Text { get; set; }
        public string Value { get; set; }
    }
}

InformationsquelleAutor der Antwort lostway

Serge Zab ' s Antwort war genau das, was ich suchte. Als ein eingefleischter VB-Programmierer, ich habe portiert, um dieses VB-Modul:

'based on Serge Zab's answer on http://stackoverflow.com/questions/607188/support-for-optgroup-in-dropdownlist-net-mvc

Imports System.Collections
Imports System.Collections.Generic
Imports System.Globalization
Imports System.Linq
Imports System.Linq.Expressions
Imports System.Text
Imports System.Web
Imports System.Web.Mvc
Imports System.Web.Routing

Public Class GroupedSelectListItem
    Inherits SelectListItem
    Public Property GroupKey() As String
        Get
            Return m_GroupKey
        End Get
        Set(value As String)
            m_GroupKey = Value
        End Set
    End Property
    Private m_GroupKey As String
    Public Property GroupName() As String
        Get
            Return m_GroupName
        End Get
        Set(value As String)
            m_GroupName = Value
        End Set
    End Property
    Private m_GroupName As String
End Class

Public Module HtmlHelpers
    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String) As MvcHtmlString
        Return DropDownListHelper(htmlHelper, name, Nothing, Nothing, Nothing)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String, selectList As IEnumerable(Of GroupedSelectListItem)) As MvcHtmlString
        Return DropDownListHelper(htmlHelper, name, selectList, Nothing, Nothing)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String, optionLabel As String) As MvcHtmlString
        Return DropDownListHelper(htmlHelper, name, Nothing, optionLabel, Nothing)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String, selectList As IEnumerable(Of GroupedSelectListItem), htmlAttributes As IDictionary(Of String, Object)) As MvcHtmlString
        Return DropDownListHelper(htmlHelper, name, selectList, Nothing, htmlAttributes)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String, selectList As IEnumerable(Of GroupedSelectListItem), htmlAttributes As Object) As MvcHtmlString
        Return DropDownListHelper(htmlHelper, name, selectList, Nothing, New RouteValueDictionary(htmlAttributes))
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String, selectList As IEnumerable(Of GroupedSelectListItem), optionLabel As String) As MvcHtmlString
        Return DropDownListHelper(htmlHelper, name, selectList, optionLabel, Nothing)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String, selectList As IEnumerable(Of GroupedSelectListItem), optionLabel As String, htmlAttributes As IDictionary(Of String, Object)) As MvcHtmlString
        Return DropDownListHelper(htmlHelper, name, selectList, optionLabel, htmlAttributes)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String, selectList As IEnumerable(Of GroupedSelectListItem), optionLabel As String, htmlAttributes As Object) As MvcHtmlString
        Return DropDownListHelper(htmlHelper, name, selectList, optionLabel, New RouteValueDictionary(htmlAttributes))
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupListFor(Of TModel, TProperty)(htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TProperty)), selectList As IEnumerable(Of GroupedSelectListItem)) As MvcHtmlString
        ' optionLabel 
        ' htmlAttributes 
        Return DropDownGroupListFor(htmlHelper, expression, selectList, Nothing, Nothing)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupListFor(Of TModel, TProperty)(htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TProperty)), selectList As IEnumerable(Of GroupedSelectListItem), htmlAttributes As Object) As MvcHtmlString
        ' optionLabel 
        Return DropDownGroupListFor(htmlHelper, expression, selectList, Nothing, New RouteValueDictionary(htmlAttributes))
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupListFor(Of TModel, TProperty)(htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TProperty)), selectList As IEnumerable(Of GroupedSelectListItem), htmlAttributes As IDictionary(Of String, Object)) As MvcHtmlString
        ' optionLabel 
        Return DropDownGroupListFor(htmlHelper, expression, selectList, Nothing, htmlAttributes)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupListFor(Of TModel, TProperty)(htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TProperty)), selectList As IEnumerable(Of GroupedSelectListItem), optionLabel As String) As MvcHtmlString
        ' htmlAttributes 
        Return DropDownGroupListFor(htmlHelper, expression, selectList, optionLabel, Nothing)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupListFor(Of TModel, TProperty)(htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TProperty)), selectList As IEnumerable(Of GroupedSelectListItem), optionLabel As String, htmlAttributes As Object) As MvcHtmlString
        Return DropDownGroupListFor(htmlHelper, expression, selectList, optionLabel, New RouteValueDictionary(htmlAttributes))
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Function DropDownGroupListFor(Of TModel, TProperty)(htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TProperty)), selectList As IEnumerable(Of GroupedSelectListItem), optionLabel As String, htmlAttributes As IDictionary(Of String, Object)) As MvcHtmlString
        If expression Is Nothing Then
            Throw New ArgumentNullException("expression")
        End If

        Return DropDownListHelper(htmlHelper, ExpressionHelper.GetExpressionText(expression), selectList, optionLabel, htmlAttributes)
    End Function

    Private Function DropDownListHelper(htmlHelper As HtmlHelper, expression As String, selectList As IEnumerable(Of GroupedSelectListItem), optionLabel As String, htmlAttributes As IDictionary(Of String, Object)) As MvcHtmlString
        ' allowMultiple 
        Return SelectInternal(htmlHelper, optionLabel, expression, selectList, False, htmlAttributes)
    End Function


    ' Helper methods

    <System.Runtime.CompilerServices.Extension> _
    Private Function GetSelectData(htmlHelper As HtmlHelper, name As String) As IEnumerable(Of GroupedSelectListItem)
        Dim o As Object = Nothing
        If htmlHelper.ViewData IsNot Nothing Then
            o = htmlHelper.ViewData.Eval(name)
        End If
        If o Is Nothing Then
            Throw New InvalidOperationException([String].Format(CultureInfo.CurrentCulture, "Missing Select Data", name, "IEnumerable<GroupedSelectListItem>"))
        End If
        Dim selectList As IEnumerable(Of GroupedSelectListItem) = TryCast(o, IEnumerable(Of GroupedSelectListItem))
        If selectList Is Nothing Then
            Throw New InvalidOperationException([String].Format(CultureInfo.CurrentCulture, "Wrong Select DataType", name, o.[GetType]().FullName, "IEnumerable<GroupedSelectListItem>"))
        End If
        Return selectList
    End Function

    Friend Function ListItemToOption(item As GroupedSelectListItem) As String
        Dim builder As New TagBuilder("option") With { _
             .InnerHtml = HttpUtility.HtmlEncode(item.Text) _
        }
        If item.Value IsNot Nothing Then
            builder.Attributes("value") = item.Value
        End If
        If item.Selected Then
            builder.Attributes("selected") = "selected"
        End If
        Return builder.ToString(TagRenderMode.Normal)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Private Function SelectInternal(htmlHelper__1 As HtmlHelper, optionLabel As String, name As String, selectList As IEnumerable(Of GroupedSelectListItem), allowMultiple As Boolean, htmlAttributes As IDictionary(Of String, Object)) As MvcHtmlString
        name = htmlHelper__1.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name)
        If [String].IsNullOrEmpty(name) Then
            Throw New ArgumentException("Null Or Empty", "name")
        End If

        Dim usedViewData As Boolean = False

        ' If we got a null selectList, try to use ViewData to get the list of items.
        If selectList Is Nothing Then
            selectList = htmlHelper__1.GetSelectData(name)
            usedViewData = True
        End If

        Dim defaultValue As Object = If((allowMultiple), htmlHelper__1.GetModelStateValue(name, GetType(String())), htmlHelper__1.GetModelStateValue(name, GetType(String)))

        ' If we haven't already used ViewData to get the entire list of items then we need to
        ' use the ViewData-supplied value before using the parameter-supplied value.
        If Not usedViewData Then
            If defaultValue Is Nothing Then
                defaultValue = htmlHelper__1.ViewData.Eval(name)
            End If
        End If

        If defaultValue IsNot Nothing Then
            Dim defaultValues As IEnumerable = If((allowMultiple), TryCast(defaultValue, IEnumerable), New String() {defaultValue})
            Dim values As IEnumerable(Of String) = From value In defaultValues Select (Convert.ToString(value, CultureInfo.CurrentCulture))
            Dim selectedValues As New HashSet(Of String)(values, StringComparer.OrdinalIgnoreCase)
            Dim newSelectList As New List(Of GroupedSelectListItem)()

            For Each item As GroupedSelectListItem In selectList
                item.Selected = If((item.Value IsNot Nothing), selectedValues.Contains(item.Value), selectedValues.Contains(item.Text))
                newSelectList.Add(item)
            Next
            selectList = newSelectList
        End If

        ' Convert each ListItem to an <option> tag
        Dim listItemBuilder As New StringBuilder()

        ' Make optionLabel the first item that gets rendered.
        If optionLabel IsNot Nothing Then
            listItemBuilder.AppendLine(ListItemToOption(New GroupedSelectListItem() With { _
                 .Text = optionLabel, _
                 .Value = [String].Empty, _
                 .Selected = False _
            }))
        End If

        For Each group As Object In selectList.GroupBy(Function(i) i.GroupKey)
            Dim groupName As String = selectList.Where(Function(i) i.GroupKey = group.Key).[Select](Function(it) it.GroupName).FirstOrDefault()
            listItemBuilder.AppendLine(String.Format("<optgroup label=""{0}"" value=""{1}"">", groupName, group.Key))
            For Each item As GroupedSelectListItem In group
                listItemBuilder.AppendLine(ListItemToOption(item))
            Next
            listItemBuilder.AppendLine("</optgroup>")
        Next

        Dim tagBuilder As New TagBuilder("select") With { _
             .InnerHtml = listItemBuilder.ToString() _
        }
        TagBuilder.MergeAttributes(htmlAttributes)
        ' replaceExisting 
        TagBuilder.MergeAttribute("name", name, True)
        TagBuilder.GenerateId(name)
        If allowMultiple Then
            TagBuilder.MergeAttribute("multiple", "multiple")
        End If

        ' If there are any errors for a named field, we add the css attribute.
        Dim modelState As ModelState = Nothing
        If htmlHelper__1.ViewData.ModelState.TryGetValue(name, modelState) Then
            If modelState.Errors.Count > 0 Then
                TagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName)
            End If
        End If

        Return MvcHtmlString.Create(TagBuilder.ToString())
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Friend Function GetModelStateValue(helper As HtmlHelper, key As String, destinationType As Type) As Object
        Dim modelState As ModelState = Nothing
        If helper.ViewData.ModelState.TryGetValue(key, modelState) Then
            If modelState.Value IsNot Nothing Then
                ' culture 
                Return modelState.Value.ConvertTo(destinationType, Nothing)
            End If
        End If
        Return Nothing
    End Function

End Module

InformationsquelleAutor der Antwort Daz

In Serge Zab Antwortdata-Attribute, wie data_valuenamedont marging in der richtigen form data-valuename.

Habe ich ersetzt-code tagBuilder.MergeAttributes(htmlAttributes); im SelectInternal Methode, um diese

foreach (var htmlAttribute in htmlAttributes)
{
     tagBuilder.MergeAttribute(
        htmlAttribute.Key.Replace('_', '-'), 
        (string)htmlAttribute.Value
     );
}

InformationsquelleAutor der Antwort Bohdan Lyzanets

Brauchte ich eine Lösung zum behandeln einer Mehrfachauswahl mit optgroup, und ich verwendet, Serge Zab-Lösung. Ich habe gerade zwei Kommentare (zu lange für einen Kommentar).

• Trotz seiner Forderungen, seiner Lösung unterstützt nicht alle vorhandenen überlastungen des DropDownListFor, da es nicht unterstützt MultiSelectList oder SelectList, oft verwendet in den Modellen. Aber das ist nicht schwer, diese.

• Seine Lösung war nicht für mich arbeiten, für die Mehrfachauswahl zu initialisieren ausgewählte/nicht ausgewählte Elemente aus dem Modell : die ersten Werte waren nicht betroffen.
  Habe ich gerade geändert die folgende Methode :

  private static MvcHtmlString DropDownListHelper(...)
  {
  zurück SelectInternal(htmlHelper, optionLabel, Ausdruck, selectList, false /* allowMultiple */, htmlAttributes);
  }

:

private static MvcHtmlString DropDownListHelper(HtmlHelper htmlHelper, string expression, IEnumerable<GroupedSelectListItem> selectList, string optionLabel, IDictionary<string, object> htmlAttributes)
{
    bool allowMultiple = htmlAttributes.ContainsKey("multiple");
    return SelectInternal(htmlHelper, optionLabel, expression, selectList, allowMultiple, htmlAttributes);
}

Und es funktioniert wie erwartet.
Natürlich ist das multiple-Attribut definiert werden muss :
@Html.DropDownGroupListFor(m => m ist.Ausgewählte, Modell.Werte, neue { multiple = "multiple" })

Danke an Serge für seine Antwort.

InformationsquelleAutor der Antwort AFract