XtAppNextEvent(3Xt) XT FUNCTIONS XtAppNextEvent(3Xt)NAME
XtAppNextEvent, XtAppPending, XtAppPeekEvent, XtApp-
ProcessEvent, XtDispatchEvent, XtAppMainLoop - query and
process events and input
SYNTAX
void XtAppNextEvent(app_context, event_return)
XtAppContext app_context;
XEvent *event_return;
Boolean XtAppPeekEvent(app_context, event_return)
XtAppContext app_context;
XEvent *event_return;
XtInputMask XtAppPending(app_context)
XtAppContext app_context;
void XtAppProcessEvent(app_context, mask)
XtAppContext app_context;
XtInputMask mask;
Boolean XtDispatchEvent(event)
XEvent *event;
void XtAppMainLoop(app_context)
XtAppContext app_context;
ARGUMENTS
app_context
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.
event_return
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,
XtIMAlternateInput, and XtIMSignal. As a conve-
nience, the X Toolkit defines the symbolic name
XtIMAll to be the bitwise inclusive OR of all
event types.
DESCRIPTION
If the X event queue is empty, XtAppNextEvent flushes the
X output buffers of each Display in the application con-
text and waits for an event while looking at the other
input sources, timeout timeout values, and signal handlers
and calling any callback procedures triggered by them.
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XtAppNextEvent(3Xt) XT FUNCTIONS XtAppNextEvent(3Xt)
This wait time can be used for background processing (see
Section 7.8).
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,
XtIMAlternateInput, and XtIMSignal (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, signal source, or X event. If there is noth-
ing of the appropriate type to process, XtAppProcessEvent
blocks until there is. If there is more than one type of
thing available to process, it is undefined which will get
processed. Usually, this procedure is not called by
client applications (see XtAppMainLoop). XtAppProcess-
Event processes timer events by calling any appropriate
timer callbacks, alternate input by calling any appropri-
ate alternate input callbacks, signal source by calling
any appropriate signal 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. Xt-
DispatchEvent 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
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XtAppNextEvent(3Xt) XT FUNCTIONS XtAppNextEvent(3Xt)
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
unless XtAppSetExitFlag is called. Applications are
expected to exit in response to some user action. There
is nothing special about XtAppMainLoop; it is simply an
loop that calls XtAppNextEvent and then XtDispatchEvent,
until XtAppGetExitFlag() returns true.
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
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