Public Class DragDropListBox

    Inherits ListBox

    ''' <summary>
    ''' ドラッグアンドドロップされるアイテムのデータ
    ''' </summary>
    Private Structure DragDropItemData

        Public Sub New(ByVal index As Integer)

            m_Index = index

        End Sub

        Private m_Index As Integer

        Public ReadOnly Property Index() As Integer
            Get
                Return m_Index
            End Get
        End Property

    End Structure

    ''' <summary>
    ''' 
    ''' </summary>
    Public Sub New()

        MyBase.New()

        Me.AllowDrop = True

    End Sub

    ' ドラッグアンドドロップの開始点
    Private mouseDownPoint As Point

    ' ドラッグするアイテムのインデックス
    Private dragDropSourceItemIndex As Integer

    ''' <summary>
    ''' MouseDown
    ''' </summary>
    Protected Overrides Sub OnMouseDown(ByVal e As MouseEventArgs)

        If (e.Button And MouseButtons.Left) = MouseButtons.Left Then

            ' ドラッグアンドドロップの開始点
            mouseDownPoint = New Point(e.X, e.Y)

            dragDropSourceItemIndex = Me.IndexFromPoint(e.X, e.Y)

        Else

            mouseDownPoint = Point.Empty

            dragDropSourceItemIndex = ListBox.NoMatches

        End If

        MyBase.OnMouseDown(e)

    End Sub

    ''' <summary>
    ''' MouseUp
    ''' </summary>
    Protected Overrides Sub OnMouseUp(ByVal e As MouseEventArgs)

        mouseDownPoint = Point.Empty

        MyBase.OnMouseUp(e)

    End Sub

    ''' <summary>
    ''' MouseMove
    ''' </summary>
    Protected Overrides Sub OnMouseMove(ByVal e As MouseEventArgs)

        If (e.Button And MouseButtons.Left) = MouseButtons.Left Then

            ' ドラッグアンドドロップの範囲にあるか否かをチェックする
            Dim dragBound As Rectangle = New Rectangle(e.X - SystemInformation.DragSize.Width \ 2, e.Y - SystemInformation.DragSize.Height \ 2, SystemInformation.DragSize.Width, SystemInformation.DragSize.Height)

            If Not dragBound.Contains(mouseDownPoint) AndAlso dragDropSourceItemIndex <> ListBox.NoMatches Then

                ' ドラッグアンドドロップ用のデータを作成
                Dim itemData As DragDropItemData = New DragDropItemData(dragDropSourceItemIndex)

                ' アイテムをドラッグアンドドロップする
                Dim effects As DragDropEffects = Me.DoDragDrop(itemData, DragDropEffects.Move)

            End If

        End If

        MyBase.OnMouseMove(e)

    End Sub

    ''' <summary>
    ''' DragEnter
    ''' </summary>
    Protected Overrides Sub OnDragEnter(ByVal drgevent As DragEventArgs)

        If drgevent.Data.GetDataPresent(GetType(DragDropItemData)) Then

            drgevent.Effect = DragDropEffects.Move

        Else

            drgevent.Effect = DragDropEffects.None

        End If

        MyBase.OnDragEnter(drgevent)

    End Sub

    ''' <summary>
    ''' DragDrop
    ''' </summary>
    Protected Overrides Sub OnDragDrop(ByVal drgevent As DragEventArgs)

        If drgevent.Data.GetDataPresent(GetType(DragDropItemData)) Then

            ' 入れ替え先のインデックス
            Dim targetIndex As Integer = Me.IndexFromPoint(Me.PointToClient(New Point(drgevent.X, drgevent.Y)))

            If targetIndex = ListBox.NoMatches Then targetIndex = Me.Items.Count - 1

            ' ドラッグアンドドロップするアイテムのデータを取得
            Dim itemData As DragDropItemData = DirectCast(drgevent.Data.GetData(GetType(DragDropItemData)), DragDropItemData)

            ' アイテムを入れかえる
            Dim temp As Object = Me.Items(itemData.Index)

            Me.Items(itemData.Index) = Me.Items(targetIndex)

            Me.Items(targetIndex) = temp

            ' 入れ替えたアイテムを選択する
            Me.SelectedItem = temp

        End If

        MyBase.OnDragDrop(drgevent)

    End Sub

End Class