XtGrabKeyboard() XtGrabKeyboard()
Name
XtGrabKeyboard - actively grab the keyboard.
Synopsis
int XtGrabKeyboard(widget, owner_events, pointer_mode, keyboard_mode, time)
Widget widget;
Boolean owner_events;
int pointer_mode, keyboard_mode;
Time time;
Inputs
widget Specifies the widget for whose window the keyboard is to be grabbed. Must be of class Core or any subclass thereof.
owner_events
Specifies whether the pointer events are to be reported normally within this application (pass True) or only to the grab window
(pass False).
pointer_mode
Controls processing of pointer events during the grab. Either GrabModeSync or GrabModeAsync.
keyboard_mode
Controls processing of keyboard events during the grab. Either GrabModeSync or GrabModeAsync.
time Specifies the time when the grab should take place. Pass either a timestamp (from an event) or the constant CurrentTime.
Description
If the specified widget is realized XtGrabKeyboard() calls XGrabKeyboard() specifying the widget's window as the grab_window, passing its
remaining argument unmodified, and returning whatever XGrabKeyboard() returns. If the widget is not realized, XGrabKeyboard() immediately
returns GrabNotViewable. No future automatic ungrab is implied by XtGrabKeyboard().
See the "Background" section below for a description of the arguments and an explanation of event processing during an active keyboard
grab.
Usage
When the keyboard is grabbed, all key events are delivered to the widget you specify or to your application, regardless of the location of
the pointer. There are not many occasions when this is a reasonable thing to do, because it locks out input to other applications. xterm
grabs the keyboard to implement secure mode.
Most applications will never need to issue a grab. XtAddGrab() (called by XtPopup()) can be used to implement modal popups inside an
application, and XtSetKeyboardFocus() can be used to redirect keyboard focus within an application. Neither function actually issues a
grab, and so does not interrupt event processing by other clients.
To cancel an active keyboard grab, use XtUngrabKeyboard().
Background
The XGrabKeyboard() function actively grabs control of the keyboard and generates FocusIn and FocusOut events. Further key events are
reported only to the grabbing client. XGrabKeyboard() overrides any active keyboard grab by this client. If owner_events is False, all
generated key events are reported with respect to grab_window. If owner_events is True and if a generated key event would normally be
reported to this client, it is reported normally; otherwise, the event is reported with respect to the grab_window. Both KeyPress and
KeyRelease events are always reported, independent of any event selection made by the client.
If the keyboard_mode argument is GrabModeAsync, keyboard event processing continues as usual. If the keyboard is currently frozen by this
client, then processing of keyboard events is resumed. If the keyboard_mode argument is GrabModeSync, the state of the keyboard (as seen
by client applications) appears to freeze, and the X server generates no further keyboard events until the grabbing client issues a releas-
ing XAllowEvents() call or until the keyboard grab is released. Actual keyboard changes are not lost while the keyboard is frozen; they
are simply queued in the server for later processing.
If pointer_mode is GrabModeAsync, pointer event processing is unaffected by activation of the grab. If pointer_mode is GrabModeSync, the
state of the pointer (as seen by client applications) appears to freeze, and the X server generates no further pointer events until the
grabbing client issues a releasing XAllowEvents() call or until the keyboard grab is released. Actual pointer changes are not lost while
the pointer is frozen; they are simply queued in the server for later processing.
If the keyboard is actively grabbed by some other client, XGrabKeyboard() fails and returns AlreadyGrabbed. If grab_window is not view-
able, it fails and returns GrabNotViewable. If the keyboard is frozen by an active grab of another client, it fails and returns
GrabFrozen. If the specified time is earlier than the last-keyboard-grab time or later than the current X server time, it fails and
returns GrabInvalidTime. Otherwise, the last-keyboard-grab time is set to the specified time (CurrentTime is replaced by the current X
server time).
XGrabKeyboard() can generate BadValue and BadWindow errors.
See Also
XtAddGrab(1), XtGrabButton(1), XtGrabKey(1), XtGrabPointer(1), XtRegisterGrabAction(1), XtUngrabButton(1), XtUngrabKey(1), XtUngrabKey-
board(1), XtUngrabPointer(1).
Xt - Keyboard Handling XtGrabKeyboard()