Supporto per optgroup nell'elenco a discesa MVC .NET?

Question

Continuando da questa domanda creando a livello di codice un elenco a discesa Vorrei che anche il mio elenco avesse diverse liste optgroup . È attualmente possibile?

So che devo passare un elenco di selezione a un elenco a discesa ma non so come aggiungere testo, valore, optgroup all'elenco di selezione.

Voglio che il risultato finale produca:

<option value="">Please select</option>
  <optgroup label="Option A">
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
    <option value="4">4</option>
  </optgroup>
  <optgroup label="Option B">
    <option value="a">A</option>
    <option value="b">B</option>
    <option value="c">C</option>
  </optgroup>
</option>

Answer 1

Guardando il codice su www.codeplex.com/aspnet , non sembra che nessuno dei due il SelectList né il metodo di estensione DropDownList supportano l'utilizzo di OptGroup in una selezione. Sembra che dovrai scrivere il tuo metodo di estensione ed estendere SelectListItem per contenere il raggruppamento o generare manualmente la selezione nel markup.

Answer 2

La mia estensione è un po 'più complicata, ma ha tutti i sovraccarichi come DropDownList originale.

In realtà l'ho creato appositamente per essere in grado di produrre DropDownList con gruppi e per essere trasformato in due selezioni unite con l'aiuto di 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;
    }

}

Answer 3

Questo è stato aggiunto ad ASP.Net MVC alla versione 5.2 ed è ora integrato.

La Proprietà del gruppo in SelectListItem consente di specificare un gruppo per ciascun elemento:

Nuovi Costruttori SelectList consente inoltre di fornire il nome del campo che contiene il titolo del gruppo nell'elenco di articoli fornito.

I metodi HtmlHelper DropDownList e DropDownListFor ora generano elementi optgroup in base ai gruppi inclusi nell'elenco di elementi.

Facile!

Answer 4

Scrivo solo un'estensione per farlo, guardalo:

---

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; }
    }
}

Answer 5

Mancano annotazioni dei dati per le convalide dei client?

In risposta alla domanda di Chrno Love sopra, aggiungendo alla soluzione di Serge Zab: la correzione di Milimetric per gli attributi di convalida del client MVC3 quando si utilizza una raccolta di menu a discesa nella stessa vista:

        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");
        }

        // 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);
    }

Answer 6

La risposta di Serge Zab era esattamente quello che stavo cercando. Essendo un programmatore VB faticoso, l'ho portato su questo modulo 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
    <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

Answer 7

Ho provato la soluzione @Serge Zab che funziona bene, ma ho avuto qualche problema con la convalida discreta, dopo qualche ispezione ho trovato il problema.

Sembra che ci siano alcuni attributi obbligatori mancanti nell'elemento select se vuoi che la validazione Jquery si attivi, subito dopo aver creato il tuo TagBuilder

TagBuilder tagBuilder = new TagBuilder("select");

Aggiungi questi attributi

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

e la convalida discreta dovrebbe attivarsi.

Answer 8

In Serge Zab answer , attributi di dati, come data_valuename , non marcare nella forma corretta data-valuename .

Ho sostituito il codice tagBuilder.MergeAttributes (htmlAttributes); nel metodo SelectInternal con questo

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

Answer 9

Solo una nota sull'uso dell'estensione di Serge per creare più di un elenco di selezione nello stesso modulo. Avevo problemi a ottenere il secondo elenco di selezione per applicare i gruppi e quando ho esaminato l'html generato mi sono reso conto che entrambi avevano ricevuto lo stesso ID. Per risolvere questo problema, accedi alla funzione SelectInternal nell'estensione serge e commenta / elimina le seguenti due righe:

tagBuilder.MergeAttribute (" name " ;, name, true / * replaceExisting * /); tagBuilder.GenerateId (nome);

In alternativa puoi semplicemente passare ID univoci a ciascuno (anche se DropDownGroupListFor non accetta il parametro 'string name', quindi dovrai aggiungere un sovraccarico che lo faccia)

Answer 10

Avevo bisogno di una soluzione per gestire una selezione multipla con optgroup e ho usato la soluzione Serge Zab. Ho solo due commenti a riguardo (troppo lungo per un commento).

• Nonostante le sue affermazioni, la sua soluzione non supporta tutti i sovraccarichi esistenti di DropDownListFor, poiché non supporta MultiSelectList o SelectList, spesso utilizzati nei modelli. Ma non è difficile aggiungere questi.

• La sua soluzione non funzionava per me per la selezione multipla per inizializzare gli articoli selezionati / non selezionati dal modello: i valori iniziali non erano interessati. Ho appena modificato il seguente metodo:

  MvcHtmlString statico privato DropDownListHelper (...) {     return SelectInternal (htmlHelper, optionLabel, espressione, selectList, false / * allowMultiple * /, htmlAttributes); }

A questo:

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);
}

E ha funzionato come previsto. Naturalmente l'attributo multiplo deve essere definito: @ Html.DropDownGroupListFor (m = > m.Selected, Model.Values, new {multiple = " multiple "})

Grazie a Serge per la sua risposta.