Действие в случае прокрутки ListBox

Imports System.Windows.Forms
 
Public Class BetterListBox
    Inherits ListBox
    ' Event declaration
    Public Delegate Sub BetterListBoxScrollDelegate(Sender As Object, e As BetterListBoxScrollArgs)
    Public Event Scroll As BetterListBoxScrollDelegate
    ' WM_VSCROLL message constants
    Private Const WM_VSCROLL As Integer = &H115
    Private Const SB_THUMBTRACK As Integer = 5
    Private Const SB_ENDSCROLL As Integer = 8
 
    Protected Overrides Sub WndProc(ByRef m As Message)
        ' Trap the WM_VSCROLL message to generate the Scroll event
        MyBase.WndProc(m)
        If m.Msg = WM_VSCROLL Then
            Dim nfy As Integer = m.WParam.ToInt32() And &Hffff
            If Scroll IsNot Nothing AndAlso (nfy = SB_THUMBTRACK OrElse nfy = SB_ENDSCROLL) Then
                RaiseEvent Scroll(Me, New BetterListBoxScrollArgs(Me.TopIndex, nfy = SB_THUMBTRACK))
            End If
        End If
    End Sub
    Public Class BetterListBoxScrollArgs
        ' Scroll event argument
        Private mTop As Integer
        Private mTracking As Boolean
        Public Sub New(top As Integer, tracking As Boolean)
            mTop = top
            mTracking = tracking
        End Sub
        Public ReadOnly Property Top() As Integer
            Get
                Return mTop
            End Get
        End Property
        Public ReadOnly Property Tracking() As Boolean
            Get
                Return mTracking
            End Get
        End Property
    End Class
End Class