ExtendedDateTimePicker control with week numbers

Imports System
Imports System.ComponentModel
Imports System.Drawing
Imports System.Runtime.InteropServices
Imports System.Windows.Forms

Public Class ExtendedDateTimePicker : Inherits DateTimePicker
    Private Declare Auto Function GetWindowLong Lib "user32.dll" (ByVal hwnd As IntPtr, ByVal index As Int32) As Int32
    Private Declare Auto Function SetWindowLong Lib "user32.dll" (ByVal hwnd As IntPtr, ByVal index As Int32, ByVal value As Int32) As Int32

    Private Const GWL_STYLE As Int32 = (-16)
    Private Const MCM_FIRST As Int32 = &H1000
    Private Const MCM_GETMINREQRECT As Int32 = (MCM_FIRST + 9)
    Private Const MCS_WEEKNUMBERS As Int32 = &H4
    Private Const DTM_FIRST As Int32 = &H1000
    Private Const DTM_GETMONTHCAL As Int32 = (DTM_FIRST + 8)

    Private Declare Auto Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As IntPtr, ByVal msg As Int32, ByVal param As Int32, ByVal data As Int32) As IntPtr
    Private Declare Auto Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As IntPtr, ByVal msg As Int32, ByVal param As Int32, ByRef data As Rectangle) As Int32
    Private Declare Auto Function MoveWindow Lib "user32.dll" (ByVal hwnd As IntPtr, ByVal x As Int32, ByVal y As Int32, ByVal width As Int32, ByVal height As Int32, ByVal repaint As Boolean) As Int32

    Private _ShowWeekNumbers As Boolean

    <Browsable(True), DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)> _
    Public Property ShowWeekNumbers() As Boolean
        Get
            Return _ShowWeekNumbers
        End Get
        Set(ByVal value As Boolean)
            _ShowWeekNumbers = value
        End Set
    End Property

    Private Const WS_BORDER As Int32 = &H800000
    Protected Overloads Overrides Sub OnDropDown(ByVal e As EventArgs)
        Dim hMonthView As IntPtr = SendMessage(Me.Handle, DTM_GETMONTHCAL, 0, 0)
        Dim hMonthViewParent As Int32 = GetWindowLong(hMonthView, -8)
        Dim dwStyle As Int32 = GetWindowLong(hMonthView, GWL_STYLE)
        If Me.ShowWeekNumbers Then
            dwStyle = dwStyle Or MCS_WEEKNUMBERS Or WS_BORDER
        Else
            dwStyle = dwStyle And Not MCS_WEEKNUMBERS
        End If
        Dim rct As New Rectangle
        SetWindowLong(hMonthView, GWL_STYLE, dwStyle)
        SendMessage(hMonthView, MCM_GETMINREQRECT, 0, rct)
        MoveWindow(hMonthViewParent, 0, 0, rct.Right, rct.Bottom, True)
        MoveWindow(hMonthView, 0, 0, rct.Right, rct.Bottom, True)
        MyBase.OnDropDown(e)
    End Sub
End Class

private const Int32 WS_BORDER = 0x800000;

protected override void OnDropDown(EventArgs e)
{
	IntPtr hMonthView = SendMessage(this.Handle, DTM_GETMONTHCAL, 0, 0);
	Int32 hMonthViewParent = GetWindowLong(hMonthView, -8);
	Int32 dwStyle = GetWindowLong(hMonthView, GWL_STYLE);
	if (this.ShowWeekNumbers) {
		dwStyle = dwStyle | MCS_WEEKNUMBERS | WS_BORDER;
	} else {
		dwStyle = dwStyle & !MCS_WEEKNUMBERS;
	}
	Rectangle rct = new Rectangle();
	SetWindowLong(hMonthView, GWL_STYLE, dwStyle);
	SendMessage(hMonthView, MCM_GETMINREQRECT, 0, rct);
	MoveWindow(hMonthViewParent, 0, 0, rct.Right, rct.Bottom, true);
	MoveWindow(hMonthView, 0, 0, rct.Right, rct.Bottom, true);
	base.OnDropDown(e);
}

    
Private Const WS_BORDER As Int32 = &H800000

Protected Overloads Overrides Sub OnDropDown(ByVal e As EventArgs)
    Dim hMonthView As IntPtr = SendMessage(Me.Handle, DTM_GETMONTHCAL, 0, 0)
    Dim hMonthViewParent As Int32 = GetWindowLong(hMonthView, -8)
   Dim dwStyle As Int32 = GetWindowLong(hMonthView, GWL_STYLE)
    If Me.ShowWeekNumbers Then
        dwStyle = dwStyle Or MCS_WEEKNUMBERS Or WS_BORDER
    Else
        dwStyle = dwStyle And Not MCS_WEEKNUMBERS
    End If
    Dim rct As New Rectangle
    SetWindowLong(hMonthView, GWL_STYLE, dwStyle)
    SendMessage(hMonthView, MCM_GETMINREQRECT, 0, rct)
    MoveWindow(hMonthViewParent, 0, 0, rct.Right, rct.Bottom, True)
    MoveWindow(hMonthView, 0, 0, rct.Right, rct.Bottom, True)
    MyBase.OnDropDown(e)
End Sub