XtAppNextEvent(3)          XT FUNCTIONS         XtAppNextEvent(3)



NAME
       XtAppNextEvent, XtAppPending, XtAppPeekEvent, XtApp-
       ProcessEvent, 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, XtInput-
              Mask mask);

       Boolean XtDispatchEvent(XEvent *event);

       void XtAppMainLoop(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, XtIMAlternateIn-
                 put, and XtIMSignal.  As a convenience, 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.
       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, XtIMAlter-
       nateInput, and XtIMSignal (see XtAppProcessEvent).  If
       there are no events pending, XtAppPending flushes the out-
       put 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 XtDispatch-
       Event, 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 han-
       dlers 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
       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



X Version 11               libXt 1.0.5          XtAppNextEvent(3)