XtAppNextEvent(3Xt) XT FUNCTIONS XtAppNextEvent(3Xt)
NAME
XtAppNextEvent, XtAppPending, XtAppPeekEvent, XtAppProces-
sEvent, XtDispatchEvent, XtAppMainLoop - query and process
events and input
SYNTAX
void XtAppNextEvent(appcontext, eventreturn)
XtAppContext appcontext;
XEvent *eventreturn;
Boolean XtAppPeekEvent(appcontext, eventreturn)
XtAppContext appcontext;
XEvent *eventreturn;
XtInputMask XtAppPending(appcontext)
XtAppContext appcontext;
void XtAppProcessEvent(appcontext, mask)
XtAppContext appcontext;
XtInputMask mask;
Boolean XtDispatchEvent(event)
XEvent *event;
void XtAppMainLoop(appcontext)
XtAppContext appcontext;
ARGUMENTS
appcontext
Specifies the application context that identi-
fies the application .
event Specifies a pointer to the event structure that
is to be dispatched to the appropriate event
handler.
eventreturn
Returns the event information to the specified
event structure.
mask Specifies what types of events to process. The
mask is the bitwise inclusive OR of any combina-
tion of XtIMXEvent, XtIMTimer, and
XtIMAlternateInput. As a convenience, the X
Toolkit defines the symbolic name XtIMAll to be
the bitwise inclusive OR of all event types.
DESCRIPTION
If no input is on the X input queue, XtAppNextEvent
flushes the X output buffer and waits for an event while
looking at the other input sources and timeout values and
calling any callback procedures triggered by them. This
wait time can be used for background processing (see Sec-
tion 7.8).
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XtAppNextEvent(3Xt) XT FUNCTIONS XtAppNextEvent(3Xt)
If there is an event in the queue, XtAppPeekEvent fills in
the event and returns a nonzero value. If no X input is
on the queue, XtAppPeekEvent flushes the output buffer and
blocks until input is available (possibly calling some
timeout callbacks in the process). If the input is an
event, XtAppPeekEvent fills in the event and returns a
nonzero value. Otherwise, the input is for an alternate
input source, and XtAppPeekEvent returns zero.
The XtAppPending function returns a nonzero value if there
are events pending from the X server, timer pending, or
other input sources pending. The value returned is a bit
mask that is the OR of XtIMXEvent, XtIMTimer, and XtIMAl-
ternateInput (see XtAppProcessEvent). If there are no
events pending, XtAppPending flushes the output buffer and
returns zero.
The XtAppProcessEvent function processes one timer, alter-
nate input, or X event. If there is nothing of the appro-
priate type to process, XtAppProcessEvent blocks until
there is. If there is more than one type of thing avail-
able to process, it is undefined which will get processed.
Usually, this procedure is not called by client applica-
tions (see XtAppMainLoop). XtAppProcessEvent processes
timer events by calling any appropriate timer callbacks,
alternate input by calling any appropriate alternate input
callbacks, and X events by calling XtDispatchEvent.
When an X event is received, it is passed to
XtDispatchEvent, which calls the appropriate event han-
dlers and passes them the widget, the event, and client-
specific data registered with each procedure. If there
are no handlers for that event registered, the event is
ignored and the dispatcher simply returns. The order in
which the handlers are called is undefined.
The XtDispatchEvent function sends those events to the
event handler functions that have been previously regis-
tered with the dispatch routine. XtDispatchEvent returns
True if it dispatched the event to some handler and False
if it found no handler to dispatch the event to. The most
common use of XtDispatchEvent is to dispatch events
acquired with the XtAppNextEvent procedure. However, it
also can be used to dispatch user-constructed events.
XtDispatchEvent also is responsible for implementing the
grab semantics for XtAddGrab.
The XtAppMainLoop function first reads the next incoming X
event by calling XtAppNextEvent and then it dispatches the
event to the appropriate registered procedure by calling
XtDispatchEvent. This constitutes the main loop of X
Toolkit applications, and, as such, it does not return.
Applications are expected to exit in response to some user
action. There is nothing special about XtAppMainLoop; it
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XtAppNextEvent(3Xt) XT FUNCTIONS XtAppNextEvent(3Xt)
is simply an infinite loop that calls XtAppNextEvent and
then XtDispatchEvent.
Applications can provide their own version of this loop,
which tests some global termination flag or tests that the
number of top-level widgets is larger than zero before
circling back to the call to XtAppNextEvent.
SEE ALSO
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface
X Version 11 Release 3 3