vb教程之侦测离开Form进入其他程式

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vb教程之侦测离开Form进入其他程式

虽然Form有Activate与DeActivate的Events,但是这两个Events只对form的Focus是在
同一个Process不同Form之间的切换有效,如果我们在Form1,而Click其他的Process,
则Form1并不会产生DeActivate的Events,相同的,由其他的Process 回到Form1时,也
不会产生Activate的Events。唯一能得知的便是透过WM_ACTIVATE,其LowWord of wParam
有以下叁个值：
  WA_ACTIVE       Activated by some method other than a mouse click
  WA_CLICKACTIVE  Activated by a mouse click.
  WA_INACTIVE     Deactivated
透过Subclassing的技巧便可来解决这个问题

'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
'将之送往原来的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
'记录原本的Window Procedure的位址
preWinProc = GetWindowLong(Me.hwnd, GWL_WNDPROC)
'设定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,而使之又只送往原来的Window Procedure
ret = SetWindowLong(Me.hwnd, GWL_WNDPROC, preWinProc)
End Sub

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