WM_SYSKEYUP
The
WM_SYSKEYUP message is posted to the window with the keyboard focus when the
user releases a key that was pressed while the ALT key was held down. It also
occurs when no window currently has the keyboard focus; in this case, the
WM_SYSKEYUP message is sent to the active window. The window that receives the
message can distinguish between these two contexts by checking the context code
in the lKeyData parameter.
WM_SYSKEYUP
nVirtKey = (int) wParam; // virtual-key code
lKeyData = lParam; // key data
Parameters
nVirtKey
Value of wParam.
Specifies the virtual-key code of the key being released.
lKeyData
Value of lParam.
Specifies the repeat count, scan code, extended-key flag, context code,
previous key-state flag, and transition-state flag, as shown in the following
table:
|
Value |
Description |
|
0-15 |
Specifies
the repeat count. The value is the number of times the keystroke is repeated
as a result of the user holding down the key. The repeat count is always one
for a WM_SYSKEYUP message. |
|
16-23 |
Specifies
the scan code. The value depends on the original equipment manufacturer
(OEM). |
|
24 |
Specifies
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 |
Specifies
the context code. The value is 1 if the ALT key is down while the key is released; it is 0 if the
WM_SYSKEYDOWN message is posted to the active window because no window has
the keyboard focus. |
|
30 |
Specifies
the previous key state. The value is always 1 for a WM_SYSKEYUP message. |
|
31 |
Specifies
the transition state. The value is always 1 for a WM_SYSKEYUP message. |
Return Values
An
application should return zero if it processes this message.
Default Action
The DefWindowProc function sends a WM_SYSCOMMAND message to the top-level
window if the F10 key or the ALT key was released. The wParam parameter of the
message is set to SC_KEYMENU.
Remarks
When the
context code is zero, the message can be passed to the TranslateAccelerator function, which will handle
it as though it were a normal key message instead of a system character-key
message. This allows accelerator keys to be used with the active window even if
the active window does not have the keyboard focus.
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 lKeyData parameter.
For non-U.S.
enhanced 102-key keyboards, the right ALT key is handled as a CTRL+ALT key. The following table
shows the sequence of messages that result when the user presses and releases
this key:
|
Message |
Virtual-key
code |
|
WM_KEYDOWN |
VK_CONTROL |
|
WM_KEYDOWN |
VK_MENU |
|
WM_KEYUP |
VK_CONTROL |
|
WM_SYSKEYUP |
VK_MENU |
See Also