子分類技術(shù)的原理：要先取得原先Window Procedure所在的地址，將之記錄起來，接著設(shè)定所有的消息都先轉(zhuǎn)到我們所寫的消息處理過程上來，我們過濾傳過來的消息，尋找特定的消息進(jìn)行處理，其余的送回系統(tǒng)，由系統(tǒng)決定如何處理。等到我們不需要再處理這些特定的消息時，便取消消息的截取，即中止子分類過程。它一般需要三個過程:開始截取,消息處理,中止截取.
程序需要一個模塊，在模塊中聲明如下：
’api函數(shù)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
’定義常數(shù)Public Const GWL_WNDPROC = (-4) Public Const WM_MOUSEMOVE = &H200 Public Const WM_RBUTTONDOWN = &H204
’全局變量,存放控件標(biāo)志性數(shù)據(jù)Public preWinProc As Long
’本函數(shù)就是用來接收子分類時截取的消息的Public Function wndproc(ByVal hwnd As Long, ByVal Msg As Long, _
ByVal wParam As Long, ByVal lParam As Long) As
Long
’截取下來的消息存放在msg參數(shù)中.
if msg=WM_RBUTTONDOWN then
’檢測到鼠標(biāo)右擊消息,這里就可以加入我們的處理代碼如:
msgbox "你好,鼠標(biāo)右擊消息!"
’需要注意,如果這兒不加入任何代碼,則相當(dāng)于吃掉了這條消息. else
’如果我們不是我們需要處理的消息,則將之送回原來的程序.
wndproc = CallWindowProc(preWinProc, hwnd, Msg, wParam, lParam) endif End Function
’以下代碼在窗體中: ’本例以截取一個combobox控件的消息為例,假設(shè)該’控件的名字是:comb1 Private Sub subclass() Dim ret As Long
’記錄Window Procedure的地址
preWinProc = GetWindowLong(comb1.hwnd, GWL_WNDPROC)