c++ - WndProc 的类方法

Question

这article出色地解释了调用类成员 WndProc 的选项。我看过this response in stackoverflow但是在 CreateWindow 之后关联类成员 WndProc 的主要问题是某些消息将丢失(包括重要的 WM_CREATE)，如 the mentioned article 中所述。 .

我的问题:我想听听专家的意见，看看下面公开的哪种方法或新方法是创建类的最佳方法(性能、可维护性……)成员 WndProc。

简述文章中暴露的两个最终解决方案(假设它存在一个带有WndProc方法的Window类):

1. 具有 this 全局指针存储的每个窗口数据，使用 CRITICAL_SECTION 保护它以使其线程安全(从 here 中提取):

   // The helper window procedure
   // It is called by Windows, and thus it's a non-member function
   // This message handler will only be called after successful SetWindowLong call
   // We can assume that pointer returned by GetWindowLong is valid
   // It will route messages to our member message handler
   LRESULT CALLBACK WndProc2(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) {
     // Get a window pointer associated with this window
     Window *w = (Window *) GetWindowLong(hwnd, GWL_USERDATA);
     // It should be valid, assert so
     _ASSERT(w);
     // Redirect messages to the window procedure of the associated window
     return w->WndProc(hwnd, msg, wp, lp);
   }
   // The temporary global this pointer
   // It will be used only between CreateWindow is called and the first message is processed by WndProc
   // WARNING: it is not thread-safe.
   Window *g_pWindow;
   
   // Critical section protecting the global Window pointer
   CRITICAL_SECTION g_WindowCS;
   
   // The helper window procedure
   LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) {
     // Stash global Window pointer into per-window data area
     SetWindowLong(hwnd, GWL_USERDATA, (long) g_pWindow);
     // Unlock global critical section
     g_pWindow->HaveCSLock = false;
     LeaveCriticalSection(&g_WindowCS);
     // Reset the window message handler
     SetWindowLong(hwnd, GWL_WNDPROC, (long) WndProc2);
     // Dispatch first message to the member message handler
     return WndProc2(hwnd, msg, wp, lp);
   }
   

   现在我们可以创建窗口了:

   InitializeCriticalSection(&g_WindowCS);
   // Enter the critical section before you write to protected data
   EnterCriticalSection(&g_WindowCS);
   
   // Set global Window pointer to our Window instance
   // Moved the assignment here, where we have exclusive access to the pointer
   g_pWindow = &w;
   
   // Set a flag indicating that the window has the critical section lock
   // Note: this must be executed after the above assignment
   g_pWindow->HaveCSLock = true;
   
   // Create window
   // Note: lpParam is not used
   HWND hwnd = CreateWindow(TEXT("BaseWnd"), TEXT("Hello, World!"), WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, 0, 0, hinst, 0);
   
   // Leave critical section if window creation failed and our window procedure hasn't released it
   if (g_pWindow->HaveCSLock)
     LeaveCriticalSection(&g_WindowCS);
   // Destroy critical section
   // In production code, you'd do this when application terminates, not immediately after CreateWindow call
   DeleteCriticalSection(&g_WindowCS);
   

2. 使用 CBT Hook 程序(摘自 here):

   // The helper window procedure
   // It is called by Windows, and thus it's a non-member function
   // This message handler will only be called after successful SetWindowLong call from the hook
   // We can assume that pointer returned by GetWindowLong is valid
   // It will route messages to our member message handler
   LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp)
   {
     // Get a window pointer associated with this window
     Window *w = (Window *) GetWindowLong(hwnd, GWL_USERDATA);
     // It should be valid, assert so
     _ASSERT(w);
     // Redirect messages to the window procedure of the associated window
     return w->WndProc(hwnd, msg, wp, lp);
   }
   
   // The CBT hook procedure
   // It is called during CreateWindow call before WndProc receives any messages
   // Its job is to set per-window Window pointer to the one passed through lpParam to CreateWindow
   LRESULT CALLBACK CBTProc(int code, WPARAM wp, LPARAM lp)
   {
     if (code != HCBT_CREATEWND) {
       // Ignore everything but create window requests
       // Note: generally, HCBT_CREATEWND is the only notification we will get,
       // assuming the thread is hooked only for the duration of CreateWindow call.
       // However, we may receive other notifications, in which case they will not be passed to other CBT hooks.
       return 0;
     }
     // Grab a pointer passed to CreateWindow as lpParam
     std::pair<Window *, HHOOK> *p = (std::pair<Window *, HHOOK> *) LPCBT_CREATEWND(lp)->lpcs->lpCreateParams;
     // Only handle this window if it wasn't handled before, to prevent rehooking windows when CreateWindow is called recursively
     // ie, when you create windows from a WM_CREATE handler
     if (p->first) {
       // Stash the associated Window pointer, which is the first member of the pair, into per-window data area
       SetWindowLong((HWND) wp, GWL_USERDATA, (long) p->first);
       // Mark this window as handled
       p->first = 0;
     }
     // Call the next hook in chain, using the second member of the pair
     return CallNextHookEx(p->second, code, wp, lp);
   }
   

   现在我们可以创建窗口了:

   // Install the CBT hook
   // Note: hook the thread immediately before, and unhook it immediately after CreateWindow call.
   // The hook procedure can only process window creation nofitications, and it shouldn't be called for other types of notifications
   // Additionally, calling hook for other events is wasteful since it won't do anything useful anyway
   HHOOK hook = SetWindowsHookEx(WH_CBT, CBTProc, 0, GetCurrentThreadId());
   _ASSERT(hook);
   
   // Create window
   // Pass a pair consisting of window object pointer and hook as lpParam
   std::pair<Window *, HHOOK> p(&w, hook);
   HWND hwnd = CreateWindow(TEXT("BaseWnd"), TEXT("Hello, World!"), WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, 0, 0, hinst, &p);
   
   // Unhook first
   UnhookWindowsHookEx(hook);
   

Answer 1

我个人不会使用这两种方法中的任何一种。全局变量方法有效，但感觉很脏。特别是带锁。而 CBT 钩子(Hook)，远远超出了顶部。尽管它指向了正确的方向。

在创建期间将状态信息传递给窗口过程的标准方法是通过CreateWindow 或CreateWindowEx 的lpParam 参数。所以技术如下:

1. 在 CreateWindow 或 CreateWindowEx 的 lpParam 参数中传递您的实例指针。
2. 在您的 WM_NCCREATE 处理程序中读取此值。该消息将信息作为 CREATESTRUCT 结构的一部分提供。
3. 还是在WM_NCCREATE调用SetWindowLongPtr将窗口的用户数据设置为实例指针。
4. 所有将来对窗口过程的调用现在都可以通过调用 GetWindowLongPtr 来获取实例指针。

Raymond Chen 在此处说明了详细信息:How can I make a WNDPROC or DLGPROC a member of my C++ class?