一篇针对键盘技术非常不错的文章，由于时间关系没有翻译，看不懂的地方大家共同讨论。
A windows application learns of keyboard events the same way it learns about mouse events: through messages. a program receives a message whenever a key is pressed or released. if you want to know when the page up or page down key is pressed so that your application can react accordingly, you process wm_keydown messages and check for key codes identifying the page up or page down key. if you'd rather know when a key is released, you process wm_keyup messages instead. for keys that produce printable characters, you can ignore key-down and key-up messages and process wm_char messages that denote characters typed at the keyboard. relying on wm_char messages instead of wm_keyup/down messages simplifies character processing by enabling windows to factor in events and circumstances surrounding the keystroke, such as whether the shift key is pressed, whether caps lock is on or off, and differences in keyboard layouts.
the input focus
like the mouse, the keyboard is a global hardware resource shared by all applications. windows decides which window to send mouse messages to by identifying the window under the cursor. keyboard messages are targeted differently. windows directs keyboard messages to the window with the "input focus." at any given time, no more than one window has the input focus. often the window with the input focus is the main window of the active application. however, the input focus might belong to a child of the main window or to a control in a dialog box. regardless, windows always sends keyboard messages to the window that owns the focus. if your application's window has no child windows, keyboard processing is relatively straightforward: when your application is active, its main window receives keyboard messages. if the focus shifts to a child window, keyboard messages go to the child window instead and the flow of messages to the main window ceases.
windows notifies a window that it is about to receive or lose the input focus with wm_setfocus and wm_killfocus messages, which mfc programs process as shown here:
// in cmainwindow's message map
on_wm_setfocus ()
on_wm_killfocus ()
void cmainwindow::onsetfocus (cwnd* poldwnd)
{
// cmainwindow now has the input focus. poldwnd
// identifies the window that lost the input focus.
// poldwnd will be null if the window that lost the
// focus was created by another thread.
}
void cmainwindow::onkillfocus (cwnd* pnewwnd)
{
// cmainwindow is about to lose the input focus.
// pnewwnd identifies the window that will receive
// the input focus. pnewwnd will be null if the
// window that's receiving the focus is owned by
// another thread.
}
an application can shift the input focus to another window with cwnd::setfocus:
pwnd->setfocus ();
or it can use the static cwnd::getfocus function to find out who currently has the input focus:
cwnd* pfocuswnd = cwnd::getfocus ();
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2008/12/12 10:12:00
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Getting Input from the Keyboard(3050字) － 卷积内核，2008年12月12日
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