子分类技术的原理：要先取得原先Window Procedure所在的地址，将之记录起来，接着设定所有的消息都先转到我们所写的消息处理过程上来，我们过滤传过来的消息，寻找特定的消息进行处理，其余的送回系统，由系统决定如何处理。等到我们不需要再处理这些特定的消息时，便取消消息的截取，即中止子分类过程。它一般需要三个过程:开始截取,消息处理,中止截取.
程序需要一个模块，在模块中声明如下：
'API函数Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" _
(ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) A s 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
'定义常数Public Const GWL_WNDPROC = (-4) Public Const WM_MOUSEMOVE = &H200 Public Const WM_RBUTTONDOWN = &H204
'全局变量,存放控件标志性数据Public preWinProc As Long
'本函数就是用来接收子分类时截取的消息的Public Function wndproc(ByVal hwnd As Long, ByVal Msg As Long, _
ByVal wParam As Long, ByVal lParam As Long) As
Long
'截取下来的消息存放在msg参数中.
if msg=WM_RBUTTONDOWN then
'检测到鼠标右击消息,这里就可以加入我们的处理代码如:
msgbox "你好,鼠标右击消息!"
'需要注意,如果这儿不加入任何代码,则相当于吃掉了这条消息. else
'如果我们不是我们需要处理的消息,则将之送回原来的程序.
wndproc = CallWindowProc(preWinProc, hwnd, Msg, wParam, lParam) endif End Function
++++++++++++++++++++++++++++++++++++++++++++++++++++ '以下代码在窗体中: '本例以截取一个combobox控件的消息为例,假设该'控件的名字是:comb1 Private Sub subclass() Dim ret As Long
'记录Window Procedure的地址
preWinProc = GetWindowLong(comb1.hwnd, GWL_WNDPROC)
'开始截取消息,并将消息交给wndproc过程处理.
ret = SetWindowLong(comb1.hwnd, GWL_WNDPROC, AddressOf wndproc) End Sub
Private Sub EndSubclass()
Dim ret As Long
'取消消息截取，结束子分类过程.
ret = SetWindowLong(comb1.hwnd, GWL_WNDPROC, preWinProc) End Sub
'当要截取其它控件的消息时,只需要将subclass与EndSubclass过程中的comb1.h wnd换成该控件的控件.hwnd即可. '调试过程中注意存盘,因为如果一时不慎会造成死机.
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