XtAppNextEvent(3Xt) XtAppNextEvent(3Xt)
NAME
XtAppNextEvent, XtAppPending, XtAppPeekEvent,
XtAppProcessEvent, XtDispatchEvent, XtAppMainLoop -
query and process events and input
SYNOPSIS
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
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XtAppNextEvent(3Xt) XtAppNextEvent(3Xt)
values and calling any callback procedures triggered by
them. This wait time can be used for background
processing.
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
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XtAppNextEvent(3Xt) XtAppNextEvent(3Xt)
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 Programming Manual
Xlib Programming Manual
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