Public Class ComboBox
    Inherits Windows.Forms.ComboBox
    ''' <summary>
    ''' Hilfs-Klasse, die User32 API Funktionen enthält.
    ''' </summary>
    ''' <remarks></remarks>
    Private Class User32
        <StructLayout(LayoutKind.Sequential)> _
        Public Structure RECT
            Public left As Integer
            Public top As Integer
            Public right As Integer
            Public bottom As Integer
        End Structure
 
        <DllImport("user32.dll")> _
        Public Shared Function GetWindowRect(ByVal hWnd As IntPtr, _
          ByRef rect As RECT) As IntPtr
        End Function
 
 
Protected Overrides Sub OnMouseMove(ByVal e As _
  System.Windows.Forms.MouseEventArgs)
        Dim myPosition As User32.RECT
        User32.GetWindowRect(Me.Handle, myPosition)
        If Windows.Forms.Cursor.Position.Y < myPosition.top + Me.Height _
        And Windows.Forms.Cursor.Position.Y > myPosition.top + 21 Then
            If Me.Items.Count - 1 >= CInt(Math.Ceiling(( _
              Windows.Forms.Cursor.Position.Y - (myPosition.top + _
              _defaultHight)) / Me.ItemHeight)) - 1 Then
               Me.SelectedIndex = CInt(Math.Ceiling(( _
               Windows.Forms.Cursor.Position.Y - (myPosition.top + _
               _defaultHight)) / Me.ItemHeight)) - 1
            End If
        End If
        MyBase.OnMouseMove(e)
 
End Class
    End Sub