การ Lock MDI Form ใน VB.NET (Windows Forms Application)

Option Explicit
Private Const GWL_STYLE = (-16)
Private Const WS_SYSMENU = &H80000
Private Const WS_CAPTION = &HC00000
Private Const WS_THICKFRAME = &H40000
Private Const WS_MAXIMIZEBOX = &H10000
Private Const WS_MINIMIZEBOX = &H20000
Private Const SC_CLOSE As Long = &HF060&
Private Const SC_MAXIMIZE = &HF030&
Private Const SC_MINIMIZE = &HF020&
Private Const MIIM_STATE As Long = &H1&
Private Const MIIM_ID As Long = &H2&
Private Const MFS_GRAYED As Long = &H3&
Private Const WM_NCACTIVATE As Long = &H86
Private Type MENUITEMINFO
    cbSize,fMask,fType,fState,wID,hSubMenu,hbmpChecked,hbmpUnchecked,dwItemData,dwTypeData,cch As Long

End Type
Private Declare Function GetSystemMenu Lib "user32" (ByVal hwnd As Long, ByVal bRevert As Long) As Long
Private Declare Function GetMenuItemInfo Lib "user32" Alias "GetMenuItemInfoA" (ByVal hMenu As Long, ByVal un As Long, ByVal b As Boolean, lpMenuItemInfo As MENUITEMINFO) As Long
Private Declare Function SetMenuItemInfo Lib "user32" Alias "SetMenuItemInfoA" (ByVal hMenu As Long, ByVal un As Long, ByVal bool As Boolean, lpcMenuItemInfo As MENUITEMINFO) As Long
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

Public Sub DisableFormResize(frm As Form)
    Dim style As Long
    Dim hMenu As Long
    Dim MII As MENUITEMINFO
    Dim lngMenuID As Long
    Const xSC_MAXIMIZE As Long = -11
    style = GetWindowLong(frm.hwnd, GWL_STYLE)
    style = style And Not WS_THICKFRAME
    style = style And Not WS_MAXIMIZEBOX
    style = SetWindowLong(frm.hwnd, GWL_STYLE, style)
    On Error Resume Next
    hMenu = GetSystemMenu(frm.hwnd, 0)
    With MII
        .cbSize = Len(MII)
        .dwTypeData = String(80, 0)
        .cch = Len(.dwTypeData)
        .fMask = MIIM_STATE
        .wID = SC_MAXIMIZE
    End With
    If GetMenuItemInfo(hMenu, MII.wID, False, MII) = 0 Then Exit Sub
    With MII
        lngMenuID = .wID
        .wID = xSC_MAXIMIZE
        .fMask = MIIM_ID
    End With
    If SetMenuItemInfo(hMenu, lngMenuID, False, MII) = 0 Then Exit Sub
    With MII
        .fState = (.fState Or MFS_GRAYED)
        .fMask = MIIM_STATE
    End With
    If SetMenuItemInfo(hMenu, MII.wID, False, MII) = 0 Then Exit Sub
    SendMessage hwnd, WM_NCACTIVATE, True, 0
    frm.Width = frm.Width - 1
    frm.Width = frm.Width + 1
End Sub