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关机消息的拦截 -VB资料

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关机消息的拦截 -VB资料

在关机或Logff前信息的拦截

  如果我们关机或Logoff时,我们的程序有时会因而无法按正常程序结束,一般我们会在Form的Unload中一段程序结束时要做什么事,但是,如果使用者直接用开始功能菜单的关机,会使UnLoad的部份没有做到,我们现在就想办法来拦截关机(或Logoff)时的信息。

  一般来说,关机或Logff后,Windows会传依序送出WM_QUERYENDSESSION的信息给每个Process,如果中间有一个Process不能顺利结束(例如:Word修改后未存档,而出现是否存档,但我们按取消),这时该信息执行的结果会传回False(0),这时Windows也就不再继续送WM_QUERYENDSESSION给下一个Proccess。反之,如果所有的Process都可以顺利结束(也就是每个送出的WM_QUERYENDSESSION都传回True),那才代表以以顺利结束。

  不管WM_QUERYENDSESSION最后的结果是可以顺利结束或不能顺利结束,Windows会再送一个WM_ENDSESSION的信息给所有的Process,而wParam的内容便是指出是否可以顺利结束(True菜单可以,False菜单不行,在vb中则CheckwParam = 0 菜单False ,0菜单True),说到这里大概就知道该如何做啦,程序如下:
  
’以下在Form
Private Sub Form_Load()
 Dim ret As Long

 ’记录原来的Window Procedure的位址
 preWinProc = GetWindowLong(Me.hwnd, GWL_WNDPROC)
 ’设定form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
 Dim fno 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)

 ’这里只是要看看用关机的方式结束程序时,会不会执行到这里
 fno = FreeFile
 Open "c:\tt2" For Append As fno
 Print #fno, "ccc" + vbCrLf
 Close #fno
End Sub
  
’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_ENDSESSION = &H16
Public Const WM_QUERYENDSESSION = &H11
  
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
 If Msg = WM_QUERYENDSESSION Then
   Debug.Print "QryEnd", wParam, lParam
 Else
  If Msg = WM_ENDSESSION Then
   If wParam 0 Then ’代表将顺利关机或LogOff,这时便得做正常结束程序的操作
     Dim fno As Long
     Open "c:\ttt" For Output As #1
     Print #1, "hahcccc5"
     Close #1
   End If
  End If
 End If

 ’将之送往原来的Window Procedure
 wndproc = CallWindowProc(preWinProc, hwnd, Msg, wParam, lParam)
End Function
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