[Windows 編程] 如何截獲 Alt+Tab 事件

Windows 中 Alt + Tab 按鍵組合被用來在各個程式之間切換。 因此，該鍵盤訊息 (WM_KEYDOWN/UP) 是直接發給系統核心， 在應用程式中的訊息迴圈中截獲不到。

 

一個常見問題是，可是有的應用程式想在被Alt+TAB 切換到後台之間做點事情， 這時候該怎麼辦？

 

方案之一就是用底層的鍵盤鉤子，截獲整個系統的鍵盤輸入。但這樣做會導致一些效率以及穩定性問題。
另外一個比較方便安全的方案就是用 Windows Accessbility API 的 SetWinEventHook 函數， 監聽 EVENT_SYSTEM_SWITCHSTART 和 EVENT_SYSTEM_SWITCHEND 事件。

 

 

這2個事件就是對應使用者按下Alt+Tab鍵 以及 鬆開 Alt+Tab鍵，下面是MSDN的解釋：

 

EVENT_SYSTEM_SWITCHSTART	The user has pressed ALT+TAB, which activates the switch window. This event is sent by the system, never by servers. The hwnd parameter of the WinEventProc callback function identifies the window to which the user is switching. If only one application is running when the user presses ALT+TAB, the system sends an EVENT_SYSTEM_SWITCHEND event without a corresponding EVENT_SYSTEM_SWITCHSTART event.
EVENT_SYSTEM_SWITCHEND	The user has released ALT+TAB. This event is sent by the system, never by servers. The hwnd parameter of the WinEventProc callback function identifies the window to which the user has switched. If only one application is running when the user presses ALT+TAB, the system sends this event without a corresponding EVENT_SYSTEM_SWITCHSTART event.

 

範例程式碼：

 

//安裝Event Hook<br />void InstallEventHook()<br />{<br /> g_hWinEventhook = ::SetWinEventHook(<br /> EVENT_SYSTEM_SWITCHSTART , EVENT_SYSTEM_SWITCHEND, // NULL, // Handle to DLL.<br /> s_HandleWinEvent, // The callback.<br /> 0, 0, // Process and thread IDs of interest (0 = all)<br /> WINEVENT_OUTOFCONTEXT | WINEVENT_SKIPOWNPROCESS); // Flags.</p><p>}</p><p>// 回呼函數</p><p>void CALLBACK s_HandleWinEvent(HWINEVENTHOOK hook, DWORD eventWin, HWND hwnd,<br /> LONG idObject, LONG idChild,<br /> DWORD dwEventThread, DWORD dwmsEventTime)</p><p>{</p><p> switch (eventWin)<br /> {<br /> case EVENT_SYSTEM_SWITCHSTART:<br /> TRACE0("[EVENT_SYSTEM_MENUSTART] "); // Alt +Tab 被按下<br /> break;<br /> case EVENT_SYSTEM_SWITCHEND:<br /> TRACE0("[EVENT_SYSTEM_MENUEND] "); // Alt +Tab 被鬆開<br /> break;<br /> }<br /> TRACE1("hwnd=0x%.8x/n", hwnd);</p><p>}</p><p>