ASP.NET MVC ListBoxFor() with optgroup Tag support

Hello,

By default, ASP.NET MVC ListBoxFor() helper does not have support for optgroup tag. To achieve this functionality, we either use jQuery or create a custom html helper. The example below demonstrates using the latter and is a VB.NET version of what we have developed in C#.

First, we define our ViewModel class for the countries with states and selected states.

VB.NET Code:

Public Class CountriesStatesViewModel
    Public Property SelectedStates() As IEnumerable(Of String)
    Public Property CountriesAndStates() As Dictionary(Of String, IEnumerable(Of SelectListItem))
End Class

Next, we create the custom ListBoxFor() helper that supports optgroup tag.

VB.NET Code:

Public Module HtmlExtensions
 
    <Extension()>
    Public Function ListBoxFor(Of TModel, TProperty)(htmlHelper As HtmlHelper(Of TModel), expression As Expression(Of Func(Of TModel, TProperty)), _
        selectList As Dictionary(Of String, IEnumerable(Of SelectListItem)), Optional htmlAttributes As Object = Nothing) As IHtmlString
 
Dim selectTag = New TagBuilder("select")
        selectTag.Attributes.Add("name", ExpressionHelper.GetExpressionText(expression))
 
        If htmlAttributes IsNot Nothing Then
            Dim routeValues As New RouteValueDictionary(htmlAttributes)
            If Not routeValues.ContainsKey(("size").ToLower()) Then
                selectTag.Attributes.Add("size", selectList.Sum(Function(x) x.Value.Count()).ToString())
            End If
 
            For Each item In routeValues
                selectTag.Attributes.Add(item.Key, item.Value.ToString())
            Next
        Else
            selectTag.Attributes.Add("size", selectList.Sum(Function(x) x.Value.Count()).ToString())
        End If
 
        Dim optgroups = New StringBuilder()
 
        For Each kvp In selectList
            Dim optgroup = New TagBuilder("optgroup")
            optgroup.Attributes.Add("label", kvp.Key)
 
            Dim options = New StringBuilder()
 
            For Each item In kvp.Value
                Dim optionTag = New TagBuilder("option")
 
                optionTag.Attributes.Add("value", item.Value)
                optionTag.SetInnerText(item.Text)
 
If item.Selected Then
                    optionTag.Attributes.Add("selected", "selected")
                End If
 
                options.Append(optionTag.ToString(TagRenderMode.Normal))
            Next
 
            optgroup.InnerHtml = options.ToString()
 
            optgroups.Append(optgroup.ToString(TagRenderMode.Normal))
        Next
 
        selectTag.InnerHtml = optgroups.ToString()
 
        Return MvcHtmlString.Create(selectTag.ToString(TagRenderMode.Normal))
 
 
    End Function
End Module

In our controller, we add two action result methods. The Index action adds data to our model and then pass it to our view for rendering. The SaveEntry action retrieves the selected states chosen by the user.

VB.NET Code:

Function Index() As ActionResult
    Dim model As New CountriesStatesViewModel
    Dim items As New Dictionary(Of String, IEnumerable(Of SelectListItem))
    model.CountriesAndStates = New Dictionary(Of String, IEnumerable(Of SelectListItem))
 
 
    items.Add("US", New List(Of SelectListItem)() From { _
        New SelectListItem() With {.Text = "Arizona", .Value = "001", .Selected = False},
        New SelectListItem() With {.Text = "Montana", .Value = "002", .Selected = False}
    })
 
 
    items.Add("AU", New List(Of SelectListItem)() From { _
        New SelectListItem() With {.Text = "Queensland", .Value = "003", .Selected = False},
        New SelectListItem() With {.Text = "Victoria", .Value = "004", .Selected = False}
    })
 
 
    items.Add("BR", New List(Of SelectListItem)() From { _
        New SelectListItem() With {.Text = "Bahia", .Value = "005", .Selected = False},
        New SelectListItem() With {.Text = "Minas Gerais", .Value = "006", .Selected = False}
    })
 
 
    model.CountriesAndStates = items
 
 
    Return View(model)
End Function
 
 
<HttpPost>
Function SaveEntry(SelectedStates As IEnumerable(Of String)) As ActionResult
    'get selected states
    If SelectedStates IsNot Nothing Then
        If SelectedStates.Count() > 0 Then
            TempData("list") = SelectedStates.ToList() 'replace with your own code
            Return RedirectToAction("SelectionSuccess") 'replace with your own code
        End If
    End If
 
 
    Return RedirectToAction("Index") 'replace with your own code
End Function

And in our view (Index.vbhtml), make sure to reference the ViewModel class and Helper.

HTML Code:

@ModelType ASPMVCListBoxForHelper.CountriesStatesViewModel
@Imports ASPMVCListBoxForHelper.Helpers
<div>
    @Using Html.BeginForm("SaveEntry", "Home", FormMethod.Post)
        @Html.ListBoxFor(Function(t) t.SelectedStates, Model.CountriesAndStates, New With {.Multiple = "Multiple", .Size = Model.CountriesAndStates.Sum(Function(x) x.Value.Count())})
        @<br />
        @<input name="Save" type="submit" value="Save" />
    End Using
</div>

Screenshot
Attachment 138093

Source code: VB.NET Version|C# Version

That's it.. :-)