Windows未公开函数揭密――之三

在mSub.Bas中加入以下代码：
'mSub函数包括窗口的消息处理函数
Option Explicit

Private Const WM_NCDESTROY = &H82
Private Const GWL_WNDPROC = (-4)
Private Const OLDWNDPROC = "OldWndProc"

Private Declare Function GetProp Lib "user32" Alias "GetPropA" (ByVal _
        hWnd As Long, ByVal lpString As String) As Long
Private Declare Function SetProp Lib "user32" Alias "SetPropA" (ByVal _
        hWnd As Long, ByVal lpString As String, ByVal hData As Long) As Long
Private Declare Function RemoveProp Lib "user32" Alias "RemovePropA" (ByVal _
        hWnd As Long, ByVal lpString As String) 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 CallWindowProc Lib "user32" Alias "CallWindowProcA" _
        (ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal uMsg As Long, _
        ByVal wParam As Long, ByVal lParam As Long) As Long

Public Function SubClass(hWnd As Long) As Boolean
    Dim lpfnOld As Long
    Dim fSuccess As Boolean
 
    If (GetProp(hWnd, OLDWNDPROC) = 0) Then
        lpfnOld = SetWindowLong(hWnd, GWL_WNDPROC, AddressOf WndProc)
        If lpfnOld Then
            fSuccess = SetProp(hWnd, OLDWNDPROC, lpfnOld)
        End If
    End If
 
    If fSuccess Then
        SubClass = True
    Else
        If lpfnOld Then Call UnSubClass(hWnd)
        MsgBox "Unable to successfully subclass &H" & Hex(hWnd), vbCritical
    End If
End Function

Public Function UnSubClass(hWnd As Long) As Boolean
    Dim lpfnOld As Long
 
    lpfnOld = GetProp(hWnd, OLDWNDPROC)
    If lpfnOld Then
        If RemoveProp(hWnd, OLDWNDPROC) Then
            UnSubClass = SetWindowLong(hWnd, GWL_WNDPROC, lpfnOld)
        End If
    End If
End Function

Public Function WndProc(ByVal hWnd As Long, ByVal uMsg As Long, ByVal wParam As _
        Long, ByVal lParam As Long) As Long
    Select Case uMsg
        Case WM_SHNOTIFY        '处理系统消息通告函数
            Call Form1.NotificationReceipt(wParam, lParam)
        Case WM_NCDESTROY
            Call UnSubClass(hWnd)
            MsgBox "Unubclassed &H" & Hex(hWnd), vbCritical, "WndProc Error"
    End Select
   
    WndProc = CallWindowProc(GetProp(hWnd, OLDWNDPROC), hWnd, uMsg, wParam, lParam)
End Function

保存文件，然后运行程序，然后你可以在Explore中试着建立或者删除一个文件或者文件夹，在Form中可以看到你所做的操作已经被纪录并且显示到TextBox中了。
现在分析以下上面的程序，上面的程序首先调用SHChangeNotifyRegister函数将Form添加到系统消息通告链中，并利用SetWindowLong函数改变Form的缺省的消息处理函数，当接受到系统通告消息后，根据传递的参数获得系统通告的内容并且显示在文本窗口中。退出程序时调用SHChangeNotifyDeregister函数注销系统消息通告。