繼續上一個主題
直線上溯的消息
上次說到消息被轉發到了AfxWndProc，繼續。
LRESULT?CALLBACK
AfxWndProc(HWND?hWnd,?UINT?nMsg,?WPARAM?wParam,?LPARAM?lParam)?
{
????//?…
????//?all?other?messages?route?through?message?map
????CWnd*?pWnd?=?CWnd::FromHandlePermanent(hWnd);
????//?…
????return?AfxCallWndProc(pWnd,?hWnd,?nMsg,?wParam,?lParam);
}
LRESULT?AFXAPI?AfxCallWndProc(CWnd*?pWnd,?HWND?hWnd,?UINT?nMsg,
????????????????????????WPARAM?wParam?=?0,?LPARAM?lParam?=?0)?{
????//?…
????//?Catch?exceptions?thrown?outside?the?scope?of?a?callback
????//?in?debug?builds?and?warn?the?user.
????LRESULT?lResult;
????//?…
????//?delegate?to?object's?WindowProc
????lResult?=?pWnd->WindowProc(nMsg,?wParam,?lParam);
????//?…
????return?lResult;
}
LRESULT?CWnd::WindowProc(UINT?message,?WPARAM?wParam,?LPARAM?lParam)?
{
????
//
?OnWndMsg?does?most?of?the?work,?except?for?DefWindowProc?call
????LRESULT?lResult?
=
?
0
;
????
if
?(
!
OnWndMsg(message,?wParam,?lParam,?
&
lResult))
????lResult?
=
?DefWindowProc(message,?wParam,?lParam);
????
return
?lResult;
}
首先利用OnWndMsg處理消息，如果OnWndMsg沒能處理消息，調用DefWindowProc。先來看OnWndMsg，這是一個CWnd類的虛函數，這個函數的邏輯很簡單，如果消息是WM_COMMAND或WM_NOTIFY，則把消息分別交給OnCommand和OnNotify處理，否則首先在MFC內建的消息緩存中查找消息，如果命中但沒有相應的處理函數，則返回FALSE（這樣的話會交由CWnd::DefWindowProc處理），如果命中，則進一步判斷是用戶自己注冊的消息還是標準Windows消息，如果是前者，就跳到標LDispatchRegistered處理，調用相應的消息處理函數，否則就跳到LDispatch處理，調用正確的消息處理函數。
如果消息不在緩存中，那么就沿著某個類的繼承路線，由AfxFindMessageEntry在每一個類的消息映射表中查找，如果找到匹配項，同樣按照是否是用戶注冊的消息的邏輯對消息進行處理，如果始終沒有找到匹配項，則返回FALSE，交由CWnd::DefWindowProc處理。
BOOL?CWnd::OnWndMsg(UINT?message,?WPARAM?wParam,?LPARAM?lParam,?LRESULT
*
?pResult)
{
????
//
?
????
//
?special?case?for?commands
????
if
?(message?
==
?WM_COMMAND)
????
{
????????
if
?(OnCommand(wParam,?lParam))??
//
?對WM_COMMAND交給OnCommand處理
????????
{
????????????lResult?
=
?
1
;
????????????
goto
?LReturnTrue;
????????}
????????
return
?FALSE;
????}
????
//
?special?case?for?notifies
????
if
?(message?
==
?WM_NOTIFY)
????
{
????????NMHDR
*
?pNMHDR?
=
?(NMHDR
*
)lParam;
????????
if
?(pNMHDR
->
hwndFrom?
!=
?NULL?
&&
?OnNotify(wParam,?lParam,?
&
lResult))
????????????
goto
?LReturnTrue;
????????
return
?FALSE;
????}
????
//
?…?…
????
const
?AFX_MSGMAP
*
?pMessageMap;?pMessageMap?
=
?GetMessageMap();?
//
?獲取類的消息映射表
????
//
?
????AFX_MSG_CACHE
*
?pMsgCache;?
????pMsgCache?
=
?
&
_afxMsgCache[iHash];
????
const
?AFX_MSGMAP_ENTRY
*
?lpEntry;
????
//
?判斷消息是否在緩存中
????
if
?(message?
==
?pMsgCache
->
nMsg?
&&
?pMessageMap?
==
?pMsgCache
->
pMessageMap)?
{
????????
//
?cache?hit
????????lpEntry?
=
?pMsgCache
->
lpEntry;
????????AfxUnlockGlobals(CRIT_WINMSGCACHE);
????????
if
?(lpEntry?
==
?NULL)?
//
?在緩存中，但是沒有相應的表項，返回FALSE
????????
return
?FALSE;
????????
//
?cache?hit,?and?it?needs?to?be?handled
????????
if
?(message?
<
?
0xC000
)?
//
?否則，按照是否是用戶自定義的消息，?跳轉到相應的位置
????????????
goto
?LDispatch;?
//
?標準Windows消息
????????
else
????????????
goto
?LDispatchRegistered;?
//
?用戶自定義消息
????}
????
else
?
//
?如果消息不在緩存中，就只好挨家挨戶檢查一番
????
{
????????
//
?not?in?cache,?look?for?it
????????pMsgCache
->
nMsg?
=
?message;
????????pMsgCache
->
pMessageMap?
=
?pMessageMap;
????????
//
?下面這個for循環從派生類到基類檢查每一個類的消息映射表
????????
for
?(
/**/
/*
?pMessageMap?already?init'ed?
*/
;?pMessageMap?
!=
?NULL;
????????????pMessageMap?
=
?pMessageMap
->
pBaseMap)??
{
????????????
if
?(message?
<
?
0xC000
)?
//
?如果消息是Windows標準消息
????????????
{
????????????????
//
?constant?window?message
????????????????
if
?((lpEntry?
=
?AfxFindMessageEntry(pMessageMap
->
lpEntries,
????????????????message,?
0
,?
0
))?
!=
?NULL)?
{
????????????????????pMsgCache
->
lpEntry?
=
?lpEntry;
????????????????????AfxUnlockGlobals(CRIT_WINMSGCACHE);
????????????????????
goto
?LDispatch;?
//
?如果找到對應項,就轉去處理
????????????????}
????????????}
????????????
else
?
//
?如果是用戶自定義消息
????????????
{
????????????????
//
?registered?windows?message
????????????????lpEntry?
=
?pMessageMap
->
lpEntries;
????????????????
while
?((lpEntry?
=
?AfxFindMessageEntry(lpEntry,?
0xC000
,?
0
,?
0
))?
!=
?NULL)
????????????????
{
????????????????????UINT
*
?pnID?
=
?(UINT
*
)(lpEntry
->
nSig);
????????????????????ASSERT(
*
pnID?
>=
?
0xC000
?
||
?
*
pnID?
==
?
0
);
????????????????????
//
?must?be?successfully?registered
????????????????????
if
?(
*
pnID?
==
?message)
????????????????????
{
????????????????????????pMsgCache
->
lpEntry?
=
?lpEntry;
????????????????????????AfxUnlockGlobals(CRIT_WINMSGCACHE);
????????????????????????
goto
?LDispatchRegistered;?
//
?如果找到就轉去處理
????????????????????}
????????????????????????lpEntry
++
;??????
//
?keep?looking?past?this?one
????????????????}
????????????}
????????}
????????
//
?即不在緩存中，所有的類也都對此消息置之不理，那么就返回FALSE，交由CWnd::DefWndProc
????????
//
?處理
????????pMsgCache
->
lpEntry?
=
?NULL;
????????AfxUnlockGlobals(CRIT_WINMSGCACHE);
????????
return
?FALSE;
????}
????
//
?下面是對Windows標準消息和用戶自定義消息的處理
LDispatch:
????ASSERT(message?
<
?
0xC000
);
????mmf.pfn?
=
?lpEntry
->
pfn;
????
switch
?(lpEntry
->
nSig)
????
{
????
default
:
????????ASSERT(FALSE);
????????
break
;
????
case
?AfxSig_b_D_v:
????????lResult?
=
?(
this
->*
mmf.pfn_b_D)(CDC::FromHandle(reinterpret_cast
<
HDC
>
(wParam)));
????????
break
;
????
case
?AfxSig_b_b_v:
????????lResult?
=
?(
this
->*
mmf.pfn_b_b)(static_cast
<
BOOL
>
(wParam));
????????
break
;
????
case
?AfxSig_b_u_v:
????????lResult?
=
?(
this
->*
mmf.pfn_b_u)(static_cast
<
UINT
>
(wParam));
????????
break
;
????
case
?AfxSig_b_h_v:
????????lResult?
=
?(
this
->*
mmf.pfn_b_h)(reinterpret_cast
<
HANDLE
>
(wParam));
????????
break
;
????????
//
?…?…
????}
?
goto
?LReturnTrue;
LDispatchRegistered:????
//
?for?registered?windows?messages
????ASSERT(message?
>=
?
0xC000
);
????ASSERT(
sizeof
(mmf)?
==
?
sizeof
(mmf.pfn));
????mmf.pfn?
=
?lpEntry
->
pfn;
????lResult?
=
?(
this
->*
mmf.pfn_l_w_l)(wParam,?lParam);
LReturnTrue:
????
if
?(pResult?
!=
?NULL)
?????
*
pResult?
=
?lResult;
????
return
?TRUE;
}
寫到這里，對于直線上溯的消息的處理過程，應該是很清楚了，概括一下，就是先準備好兩個處理過程，一個用來處理標準Windows消息，一個用來處理用戶自定義消息，之后，根據消息是不是在緩存中，進行不同的查找，如果找到，根據消息的類型轉到不同的處理過程中去，如果處理過了，就返回TRUE，否則返回FALSE，交由CWnd::DefWindowProc處理。到此，關于直線上溯消息的處理就結束了，很簡單，無非就是從派生類到基類的一個比較操作，真正復雜些的是MFC對于WM_COMMAND消息的處理，我們后面再說了。