雖然Form有Activate與DeActivate的Events,但是這兩個Events只對form的Focus是在  
同一個Process不同Form之間的切換有效,如果我們在Form1,而Click其他的Process,  
則Form1并不會產生DeActivate的Events,相同的,由其他的Process 回到Form1時,也  
不會產生Activate的Events。唯一能得知的便是透過WM_ACTIVATE,其LowWord of wParam  
有以下叁個值：  
  WA_ACTIVE       Activated by some method other than a mouse click  
  WA_CLICKACTIVE  Activated by a mouse click.  
  WA_INACTIVE     Deactivated  
透過Subclassing的技巧便可來解決這個問題  

'以下在.bas  
Option Explicit  

Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _  
  (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long  
Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" _  
  (ByVal hwnd As Long, ByVal nIndex As Long) As Long  
Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" _  
  (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal Msg As Long, _  
   ByVal wParam As Long, ByVal lParam As Long) As Long  

Public Const GWL_WNDPROC = (-4)  
Public Const WM_ACTIVATE = &H6  
Public Const WA_ACTIVE = 1  
Public Const WA_CLICKACTIVE = 2  
Public Const WA_INACTIVE = 0  


Public preWinProc As Long  

Public Function wndproc(ByVal hwnd As Long, ByVal Msg As Long, _  
                         ByVal wParam As Long, ByVal lParam As Long) As Long  
Dim fActive As Integer  
If Msg = WM_ACTIVATE Then  
    '取得wParam的LowWord  
    fActive = CInt(wParam And &HFFFF)  
    If fActive = WA_INACTIVE Then  
       Debug.Print "InActive "  
    Else  
       Debug.Print "Active"  
    End If  
End If  
'將之送往原來的Window Procedure  
wndproc = CallWindowProc(preWinProc, hwnd, Msg, wParam, lParam)  
End Function  

'以下在form  
Option Explicit  
Private Sub Form_Activate()  
Debug.Print "Event Activate"  
End Sub  

Private Sub Form_Deactivate()  
Debug.Print "Event DeActivate"  
End Sub  

Private Sub Form_Load()  
Dim ret As Long  
'記錄原本的Window Procedure的位址  
preWinProc = GetWindowLong(Me.hwnd, GWL_WNDPROC)  
'設定Combo1的window Procedure到wndproc  
ret = SetWindowLong(Me.hwnd, GWL_WNDPROC, AddressOf wndproc)  
End Sub  

Private Sub Form_Unload(Cancel As Integer)  
Dim ret As Long  
'取消Message的截取,而使之又只送往原來的Window Procedure  
ret = SetWindowLong(Me.hwnd, GWL_WNDPROC, preWinProc)  
End Sub