XtAppNextEvent(3Xt) X Version 11 (Release 3) XtAppNextEvent(3Xt)
NAME
XtAppNextEvent, XtAppPending, XtAppPeekEvent,
XtAppProcessEvent, 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 identifies
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
combination 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 Section 7.8).
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XtAppNextEvent(3Xt) X Version 11 (Release 3) 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
XtIMAlternateInput (see XtAppProcessEvent). If there are no
events pending, XtAppPending flushes the output buffer and
returns zero.
The XtAppProcessEvent function processes one timer,
alternate input, or X event. If there is nothing 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). 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 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 XtDispatchEvent function sends those events to the event
handler functions that have been previously registered 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.
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XtAppNextEvent(3Xt) X Version 11 (Release 3) XtAppNextEvent(3Xt)
Applications are expected to exit in response to some user
action. There is nothing special about XtAppMainLoop; it 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
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