Soporte para optgroup en la lista desplegable .NET MVC?

Continuando con esta pregunta , creando programáticamente una lista desplegable, me gustaría que mi lista también tenga varias listas de optgroup . ¿Es esto posible actualmente?

Sé que necesito pasar una lista de selección a dropDownList pero no sé cómo agregar texto, valor, optgroup a la lista de selección.

Quiero que el resultado final produzca:

 Please select  1 2 3 4   A B C   

Si mira el código en http://www.codeplex.com/aspnet , no parece que ni SelectList ni el método de extensión DropDownList admiten el uso de OptGroup en una selección. Parece que tendrá que escribir su propio método de extensión y extender SelectListItem para contener la agrupación o generar la selección manualmente en el marcado.

Mi extensión es un poco más complicada, pero tiene todas las sobrecargas que tiene DropDownList original.

En realidad, lo he creado especialmente para poder producir DropDownList con grupos y para transformarlo en dos selecciones unidas con la ayuda de 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 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 selectList, IDictionary htmlAttributes) { return DropDownListHelper(htmlHelper, name, selectList, null, htmlAttributes); } public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable selectList, object htmlAttributes) { return DropDownListHelper(htmlHelper, name, selectList, null, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes)); } public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable selectList, string optionLabel) { return DropDownListHelper(htmlHelper, name, selectList, optionLabel, null); } public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable selectList, string optionLabel, IDictionary htmlAttributes) { return DropDownListHelper(htmlHelper, name, selectList, optionLabel, htmlAttributes); } public static MvcHtmlString DropDownGroupList(this HtmlHelper htmlHelper, string name, IEnumerable selectList, string optionLabel, object htmlAttributes) { return DropDownListHelper(htmlHelper, name, selectList, optionLabel, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes)); } public static MvcHtmlString DropDownGroupListFor(this HtmlHelper htmlHelper, Expression> expression, IEnumerable selectList) { return DropDownGroupListFor(htmlHelper, expression, selectList, null /* optionLabel */, null /* htmlAttributes */); } public static MvcHtmlString DropDownGroupListFor(this HtmlHelper htmlHelper, Expression> expression, IEnumerable selectList, object htmlAttributes) { return DropDownGroupListFor(htmlHelper, expression, selectList, null /* optionLabel */, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes)); } public static MvcHtmlString DropDownGroupListFor(this HtmlHelper htmlHelper, Expression> expression, IEnumerable selectList, IDictionary htmlAttributes) { return DropDownGroupListFor(htmlHelper, expression, selectList, null /* optionLabel */, htmlAttributes); } public static MvcHtmlString DropDownGroupListFor(this HtmlHelper htmlHelper, Expression> expression, IEnumerable selectList, string optionLabel) { return DropDownGroupListFor(htmlHelper, expression, selectList, optionLabel, null /* htmlAttributes */); } public static MvcHtmlString DropDownGroupListFor(this HtmlHelper htmlHelper, Expression> expression, IEnumerable selectList, string optionLabel, object htmlAttributes) { return DropDownGroupListFor(htmlHelper, expression, selectList, optionLabel, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes)); } public static MvcHtmlString DropDownGroupListFor(this HtmlHelper htmlHelper, Expression> expression, IEnumerable selectList, string optionLabel, IDictionary 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 selectList, string optionLabel, IDictionary htmlAttributes) { return SelectInternal(htmlHelper, optionLabel, expression, selectList, false /* allowMultiple */, htmlAttributes); } // Helper methods private static IEnumerable 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; 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 selectList, bool allowMultiple, IDictionary 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(values, StringComparer.OrdinalIgnoreCase); var newSelectList = new List(); 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 ", groupName, group.Key)); foreach (GroupedSelectListItem item in group) { listItemBuilder.AppendLine(ListItemToOption(item)); } listItemBuilder.AppendLine(""); } 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; } } 

Esto se agregó a ASP.Net MVC en la versión 5.2 y ahora está incorporado.

La propiedad Group en SelectListItem le permite especificar un grupo para cada elemento:

Los nuevos constructores de SelectList también le permiten proporcionar el nombre del campo que contiene el título del grupo en la lista de elementos suministrados.

Los métodos HtmlHelper DropDownList y DropDownListFor ahora generan elementos de grupo de opciones basados ​​en los grupos incluidos en la lista de elementos.

¡Fácil!

Solo escribo una extensión para hacer esto, lo veo:


 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 data, string SelectedValue, object htmlAttributes) { if (data == null && helper.ViewData != null) data = helper.ViewData.Eval(name) as IEnumerable; 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 Items { get; set; } } public class OptionItem { public string Text { get; set; } public string Value { get; set; } } } 

Anotaciones de datos para las validaciones del cliente que faltan?

En respuesta a la pregunta anterior de Chrno Love, añadiendo a la solución de Serge Zab, la corrección de Milimetric para los atributos de validación MVC3 del lado del cliente al usar una colección de menús desplegables en la misma vista:

  public static MvcHtmlString DropDownGroupListFor(this HtmlHelper htmlHelper, Expression> expression, IEnumerable selectList, string optionLabel, IDictionary htmlAttributes) { if (expression == null) { throw new ArgumentNullException("expression"); } // fixing clientside validation attributes // http://stackoverflow.com/questions/4799958/asp-net-mvc-3-unobtrusive-client-validation-does-not-work-with-drop-down-lists/8102022#8102022 var metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData); var mergedAttributes = htmlHelper.GetUnobtrusiveValidationAttributes(ExpressionHelper.GetExpressionText(expression), metadata); if (htmlAttributes != null) { foreach (PropertyDescriptor descriptor in TypeDescriptor.GetProperties(htmlAttributes)) { object value = descriptor.GetValue(htmlAttributes); mergedAttributes.Add(descriptor.Name, value); } } //return DropDownListHelper(htmlHelper, ExpressionHelper.GetExpressionText(expression), selectList, optionLabel, htmlAttributes); return DropDownListHelper(htmlHelper, ExpressionHelper.GetExpressionText(expression), selectList, optionLabel, mergedAttributes); } 

La respuesta de Serge Zab era exactamente lo que estaba buscando. Al ser un progtwigdor de VB duro, lo porté a este módulo de VB:

 '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  _ Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String) As MvcHtmlString Return DropDownListHelper(htmlHelper, name, Nothing, Nothing, Nothing) End Function  _ 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  _ Public Function DropDownGroupList(htmlHelper As HtmlHelper, name As String, optionLabel As String) As MvcHtmlString Return DropDownListHelper(htmlHelper, name, Nothing, optionLabel, Nothing) End Function  _ 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  _ 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  _ 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  _ 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  _ 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  _ 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  _ 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  _ 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  _ 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  _ 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  _ 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  _ 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")) 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")) 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  _ 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 ", groupName, group.Key)) For Each item As GroupedSelectListItem In group listItemBuilder.AppendLine(ListItemToOption(item)) Next listItemBuilder.AppendLine("") 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  _ 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 

He intentado con la solución de @Serge Zab, que funciona bien pero estaba teniendo problemas con la validación discreta, después de algunas inspecciones encontré el problema.

Parece que faltan algunos atributos necesarios en el elemento de selección si desea que la validación de Jquery se active, justo después de crear su TagBuilder

 TagBuilder tagBuilder = new TagBuilder("select"); 

Agregue estos atributos

 tagBuilder.MergeAttribute("data-val", "true",true); tagBuilder.MergeAttribute("data-val-required", "your validation message", true) 

y la validación discreta debería disparar.

En la respuesta de Serge Zab, los atributos de datos, como data_valuename , no se marcan en forma correcta data-valuename .

tagBuilder.MergeAttributes(htmlAttributes); código tagBuilder.MergeAttributes(htmlAttributes); en el método SelectInternal para esto

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

Solo una nota sobre el uso de la extensión de Serge para crear más de una lista de selección en el mismo formulario. Estaba teniendo problemas para obtener la segunda lista de selección para aplicar los grupos, y cuando examiné el html que se generaba, me di cuenta de que a ambos se les había dado la misma identificación. Para solucionar esto, vaya a la función SelectInternal en la extensión de sarge y comente / elimine las siguientes dos líneas:

tagBuilder.MergeAttribute (“nombre”, nombre, verdadero / * replaceExisting * /); tagBuilder.GenerateId (nombre);

Alternativamente, puede simplemente pasar identificadores únicos a cada uno (aunque DropDownGroupListFor no toma el parámetro ‘nombre de cadena’, por lo que tendrá que agregar una sobrecarga que sí lo haga)

Necesitaba una solución para manejar una selección múltiple con optgroup, y utilicé la solución de Serge Zab. Solo tengo dos comentarios al respecto (demasiado tiempo para un comentario).

  • A pesar de sus afirmaciones, su solución no es compatible con todas las sobrecargas existentes de DropDownListFor, ya que no es compatible con MultiSelectList o SelectList, que a menudo se usan en los modelos. Pero eso no es difícil de agregar estos.

  • Su solución no me funcionaba para Selección múltiple para inicializar elementos seleccionados / no seleccionados del modelo: los valores iniciales no se vieron afectados. Acabo de modificar el siguiente método:

    private static MvcHtmlString DropDownListHelper (…) {return SelectInternal (htmlHelper, optionLabel, expression, selectList, false / * allowMultiple * /, htmlAttributes); }

A esto :

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

Y funcionó como se esperaba. Por supuesto, el atributo múltiple debe definirse: @ Html.DropDownGroupListFor (m => m.Selected, Model.Values, new {multiple = “multiple”})

Gracias a Serge por su respuesta.