1XtAppNextEvent(3) XT FUNCTIONS XtAppNextEvent(3)
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6 XtAppNextEvent, XtAppPending, XtAppPeekEvent, XtAppProcessEvent, Xt‐
7 DispatchEvent, XtAppMainLoop - query and process events and input
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10 void XtAppNextEvent(XtAppContext app_context, XEvent *event_return);
11 Boolean XtAppPeekEvent(XtAppContext app_context, XEvent *event_return);
13 XtInputMask XtAppPending(XtAppContext app_context);
15 void XtAppProcessEvent(XtAppContext app_context, XtInputMask mask);
17 Boolean XtDispatchEvent(XEvent *event);
19 void XtAppMainLoop(XtAppContext app_context);
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23 app_context
24 Specifies the application context that identifies the appli‐
25 cation.
26 event Specifies a pointer to the event structure that is to be dis‐
28 patched to the appropriate event handler.
29 event_return
31 Returns the event information to the specified event struc‐
32 ture.
33 mask Specifies what types of events to process. The mask is the
35 bitwise inclusive OR of any combination of XtIMXEvent, XtIM‐
36 Timer, XtIMAlternateInput, and XtIMSignal. As a convenience,
37 the X Toolkit defines the symbolic name XtIMAll to be the
38 bitwise inclusive OR of all event types.
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41 If the X event queue is empty, XtAppNextEvent flushes the X output buf‐
42 fers of each Display in the application context and waits for an event
43 while looking at the other input sources, timeout timeout values, and
44 signal handlers and calling any callback procedures triggered by them.
45 This wait time can be used for background processing (see Section 7.8).
46 If there is an event in the queue, XtAppPeekEvent fills in the event
48 and returns a nonzero value. If no X input is on the queue, XtAppPeek‐
49 Event flushes the output buffer and blocks until input is available
50 (possibly calling some timeout callbacks in the process). If the input
51 is an event, XtAppPeekEvent fills in the event and returns a nonzero
52 value. Otherwise, the input is for an alternate input source, and
53 XtAppPeekEvent returns zero.
54 The XtAppPending function returns a nonzero value if there are events
56 pending from the X server, timer pending, or other input sources pend‐
57 ing. The value returned is a bit mask that is the OR of XtIMXEvent,
58 XtIMTimer, XtIMAlternateInput, and XtIMSignal (see XtAppProcessEvent).
59 If there are no events pending, XtAppPending flushes the output buffer
60 and returns zero.
61 The XtAppProcessEvent function processes one timer, alternate input,
63 signal source, or X event. If there is nothing of the appropriate type
64 to process, XtAppProcessEvent blocks until there is. If there is more
65 than one type of thing available to process, it is undefined which will
66 get processed. Usually, this procedure is not called by client appli‐
67 cations (see XtAppMainLoop). XtAppProcessEvent processes timer events
68 by calling any appropriate timer callbacks, alternate input by calling
69 any appropriate alternate input callbacks, signal source by calling any
70 appropriate signal callbacks, and X events by calling XtDispatchEvent.
71 When an X event is received, it is passed to XtDispatchEvent, which
73 calls the appropriate event handlers and passes them the widget, the
74 event, and client-specific data registered with each procedure. If
75 there are no handlers for that event registered, the event is ignored
76 and the dispatcher simply returns. The order in which the handlers are
77 called is undefined.
78 The XtDispatchEvent function sends those events to the event handler
80 functions that have been previously registered with the dispatch rou‐
81 tine. XtDispatchEvent returns True if it dispatched the event to some
82 handler and False if it found no handler to dispatch the event to. The
83 most common use of XtDispatchEvent is to dispatch events acquired with
84 the XtAppNextEvent procedure. However, it also can be used to dispatch
85 user-constructed events. XtDispatchEvent also is responsible for
86 implementing the grab semantics for XtAddGrab.
87 The XtAppMainLoop function first reads the next incoming X event by
89 calling XtAppNextEvent and then it dispatches the event to the appro‐
90 priate registered procedure by calling XtDispatchEvent. This consti‐
91 tutes the main loop of X Toolkit applications, and, as such, it does
92 not return unless XtAppSetExitFlag is called. Applications are
93 expected to exit in response to some user action. There is nothing
94 special about XtAppMainLoop; it is simply an loop that calls XtAppNext‐
95 Event and then XtDispatchEvent, until XtAppGetExitFlag() returns true.
96 Applications can provide their own version of this loop, which tests
98 some global termination flag or tests that the number of top-level wid‐
99 gets is larger than zero before circling back to the call to XtAppNext‐
100 Event.
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103 X Toolkit Intrinsics - C Language Interface
104 Xlib - C Language X Interface
105X Version 11 libXt 1.1.4 XtAppNextEvent(3)