path: root/man/XtAppNextEvent.man

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.\" $XFree86: xc/doc/man/Xt/XtAppNEv.man,v 1.5 2001/01/27 18:20:24 dawes Exp $
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.ds xL Xlib \- C Language X Interface
.ds xC Inter-Client Communication Conventions Manual
.ds Rn 3
.ds Vn 2.2
.hw XtApp-Next-Event XtApp-Pending XtApp-Peek-Event XtApp-Process-Event Xt-Dispatch-Event XtApp-Main-Loop wid-get
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.TH XtAppNextEvent 3Xt __xorgversion__ "XT FUNCTIONS"
.SH NAME
XtAppNextEvent, XtAppPending, XtAppPeekEvent, XtAppProcessEvent, XtDispatchEvent, XtAppMainLoop \- query and process events and input
.SH SYNTAX
.HP
void XtAppNextEvent(XtAppContext \fIapp_context\fP, XEvent
*\fIevent_return\fP); 
.HP
Boolean XtAppPeekEvent(XtAppContext \fIapp_context\fP, XEvent
*\fIevent_return\fP); 
.HP
XtInputMask XtAppPending(XtAppContext \fIapp_context\fP); 
.HP
void XtAppProcessEvent(XtAppContext \fIapp_context\fP, XtInputMask
\fImask\fP); 
.HP
Boolean XtDispatchEvent(XEvent *\fIevent\fP); 
.HP
void XtAppMainLoop(XtAppContext \fIapp_context\fP); 
.SH ARGUMENTS
.ds Co that identifies the application 
.IP \fIapp_context\fP 1i
Specifies the application context \*(Co.
.IP \fIevent\fP 1i
Specifies a pointer to the event structure that is to be dispatched
to the appropriate event handler.
.IP \fIevent_return\fP 1i
Returns the event information to the specified event structure.
.IP \fImask\fP 1i
Specifies what types of events to process.
The mask is the bitwise inclusive OR of any combination of
.ZN XtIMXEvent ,
.ZN XtIMTimer ,
.ZN XtIMAlternateInput ,
and
.ZN XtIMSignal .
As a convenience, the \*(tk defines the symbolic name
.ZN XtIMAll
to be the bitwise inclusive OR of all event types.
.SH DESCRIPTION
If the X event queue is empty,
.ZN XtAppNextEvent
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).
.LP
If there is an event in the queue,
.ZN XtAppPeekEvent
fills in the event and returns a nonzero value. If no X input is on the 
queue,
.ZN 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,
.ZN XtAppPeekEvent
fills in the event and returns a nonzero value.
Otherwise, the input is for an alternate input source, and
.ZN XtAppPeekEvent
returns zero.
.LP
The
.ZN 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
.ZN XtIMXEvent ,
.ZN XtIMTimer ,
.ZN XtIMAlternateInput ,
and
.ZN XtIMSignal
(see
.ZN XtAppProcessEvent ).
If there are no events pending, 
.ZN XtAppPending
flushes the output buffer and returns zero.
.LP
The
.ZN XtAppProcessEvent
function processes one timer, alternate input, signal source, or X 
event.  If there is nothing of the appropriate type to process,
.ZN 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
.ZN XtAppMainLoop ).
.ZN XtAppProcessEvent
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
.ZN XtDispatchEvent .
.LP
When an X event is received, it is passed to
.ZN 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.
.LP
The
.ZN XtDispatchEvent
function sends those events to the event handler functions that
have been previously registered with the dispatch routine.
.ZN XtDispatchEvent
returns 
.ZN True 
if it dispatched the event to some handler and
.ZN False
if it found no handler to dispatch the event to.
The most common use of
.ZN XtDispatchEvent
is to dispatch events acquired with the
.ZN XtAppNextEvent
procedure.
However, it also can be used to dispatch user-constructed events.
.ZN XtDispatchEvent
also is responsible for implementing the grab semantics for
.ZN XtAddGrab .
.LP
The
.ZN XtAppMainLoop
function first reads the next incoming X event by calling
.ZN XtAppNextEvent 
and then it dispatches the event to the appropriate registered procedure 
by calling
.ZN XtDispatchEvent .
This constitutes the main loop of \*(tk applications,
and, as such, it does not return unless
.ZN XtAppSetExitFlag
is called.
Applications are expected to exit in response to some user action.
There is nothing special about
.ZN XtAppMainLoop ;
it is simply an loop that calls
.ZN XtAppNextEvent
and then
.ZN XtDispatchEvent ,
until
.ZN XtAppGetExitFlag ()
returns true.
.LP
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
.ZN XtAppNextEvent .
.SH "SEE ALSO"
.br
\fI\*(xT\fP
.br
\fI\*(xL\fP