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).
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
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XtAppNextEvent(3Xt) X Version 11(Release 3) XtAppNextEvent(3Xt)
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. 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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