XtAppNextEvent
NAME
XtAppNextEvent, XtAppPending, XtAppPeekEvent, XtAppProcessEvent, XtDispatchEvent, XtAppMainLoop - query and process events and input
SYNTAX
void XtAppNextEvent(XtAppContext app_context, XEvent
*event_return);
Boolean XtAppPeekEvent(XtAppContext app_context, XEvent
*event_return);
XtInputMask XtAppPending(XtAppContext app_context);
void XtAppProcessEvent(XtAppContext app_context, XtInputMask
mask);
Boolean XtDispatchEvent(XEvent *event);
void XtAppMainLoop(XtAppContext app_context);
ARGUMENTS
app_context
Specifies the application context .
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 combination of
and
As a convenience, the defines the symbolic name
to be the bitwise inclusive OR of all event types.
DESCRIPTION
If the X event queue is empty,
flushes the X output buffers of each Display in the application context
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. This wait time can be used for background processing
(see Section 7.8).
If there is an event in the queue,
fills in the event and returns a nonzero value. If no X input is on the
queue,
flushes the output buffer and blocks until input is available
(possibly calling some timeout callbacks in the process).
If the input is an event,
fills in the event and returns a nonzero value.
Otherwise, the input is for an alternate input source, and
returns zero.
The
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
and
(see
If there are no events pending,
flushes the output buffer and returns zero.
The
function processes one timer, alternate input, signal source, or X
event. If there is nothing of the appropriate type to process,
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
processes timer events by calling any appropriate timer callbacks,
alternate input by calling any appropriate alternate input callbacks,
signal source by calling any appropriate signal callbacks, and X events
by calling
When an X event is received, it is passed to
which calls the appropriate event handlers
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
function sends those events to the event handler functions that
have been previously registered with the dispatch routine.
returns
if it dispatched the event to some handler and
if it found no handler to dispatch the event to.
The most common use of
is to dispatch events acquired with the
procedure.
However, it also can be used to dispatch user-constructed events.
also is responsible for implementing the grab semantics for
The
function first reads the next incoming X event by calling
and then it dispatches the event to the appropriate registered procedure
by calling
This constitutes the main loop of applications,
and, as such, it does not return unless
is called.
Applications are expected to exit in response to some user action.
There is nothing special about
it is simply an loop that calls
and then
until
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
SEE ALSO
