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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 |
