Posted to the window with the keyboard focus when a nonsystem key is pressed. A nonsystem key is a key that is pressed when the ALT key is not pressed.
The virtual-key code of the nonsystem key. See Virtual-Key Codes.
The repeat count, scan code, extended-key flag, context code, previous key-state flag, and transition-state flag, as shown following.
Bits Meaning 0-15 The repeat count for the current message. The value is the number of times the keystroke is autorepeated as a result of the user holding down the key. If the keystroke is held long enough, multiple messages are sent. However, the repeat count is not cumulative. 16-23 The scan code. The value depends on the OEM. 24 Indicates whether the key is an extended key, such as the right-hand ALT and CTRL keys that appear on an enhanced 101- or 102-key keyboard. The value is 1 if it is an extended key; otherwise, it is 0. 25-28 Reserved; do not use. 29 The context code. The value is always 0 for a WM_KEYDOWN message. 30 The previous key state. The value is 1 if the key is down before the message is sent, or it is zero if the key is up. 31 The transition state. The value is always 0 for a WM_KEYDOWN message.
An application should return zero if it processes this message.
If the F10 key is pressed, the DefWindowProc function sets an internal flag. When DefWindowProc receives the WM_KEYUP message, the function checks whether the internal flag is set and, if so, sends a WM_SYSCOMMAND message to the top-level window. The WM_SYSCOMMAND parameter of the message is set to SC_KEYMENU.
Because of the autorepeat feature, more than one WM_KEYDOWN message may be posted before a WM_KEYUP message is posted. The previous key state (bit 30) can be used to determine whether the WM_KEYDOWN message indicates the first down transition or a repeated down transition.
For enhanced 101- and 102-key keyboards, extended keys are the right ALT and CTRL keys on the main section of the keyboard; the INS, DEL, HOME, END, PAGE UP, PAGE DOWN, and arrow keys in the clusters to the left of the numeric keypad; and the divide (/) and ENTER keys in the numeric keypad. Other keyboards may support the extended-key bit in the lParam parameter.
Applications must pass wParam to TranslateMessage without altering it at all.
Minimum supported client
|Windows 2000 Professional [desktop apps only]|
Minimum supported server
|Windows 2000 Server [desktop apps only]|
Build date: 11/16/2013