This message is posted to the window with the keyboard focus when the user holds down the ALT key and then presses another key. It also occurs when no window currently has the keyboard focus; in this case, the WM_SYSKEYDOWN 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.
At a Glance
| Header file: | Winuser.h |
| Windows CE versions: | 1.0 and later |
Syntax
WM_SYSKEYDOWN nVirtKey = (int) wParam; lKeyData = lParam;
Parameters
nVirtKey
Specifies the virtual-key code of the key being pressed.
lKeyData
Specifies the repeat count, 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. |
| 29 | Specifies the context code. The value is 1 if the ALT key is held down while the key is pressed; otherwise, the value is 0. |
| 30 | Specifies the previous key state. The value is 1 if the key is down before the message is sent, or it is 0 if the key is up. |
| 31 | Specifies the transition state. The value is 1 if the key is being released, or it is 0 if the key is being pressed. |
Return Values
An application should return zero if it processes this message.
Default Action
The DefWindowProc function examines the given key and generates a WM_SYSCOMMAND message if the key is either TAB or ENTER.
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 character-key message. This enables accelerator keys to be used with the active window even if the active window does not have the keyboard focus.
Because of automatic repeat, more than one WM_SYSKEYDOWN message may occur before a WM_SYSKEYUP message is sent. The previous key state (bit 30) can be used to determine whether the WM_SYSKEYDOWN message indicates the first down transition or a repeated down transition.
For enhanced 101- and 102-key keyboards, enhanced 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.
This message is also sent when the user presses the F10 key without the ALT key.
See Also