1Tk_RestrictEvents(3) Tk Library Procedures Tk_RestrictEvents(3)
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8 Tk_RestrictEvents - filter and selectively delay X events
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11 #include <tk.h>
12 Tk_RestrictProc *
14 Tk_RestrictEvents(proc, clientData, prevClientDataPtr)
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17 Tk_RestrictProc *proc (in) Predicate procedure
18 to call to filter
19 incoming X events.
20 NULL means do not
21 restrict events at
22 all.
23 ClientData clientData (in) Arbitrary argument to
25 pass to proc.
26 ClientData *prevClientDataPtr (out) Pointer to place to
28 save argument to pre‐
29 vious restrict proce‐
30 dure.
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35 This procedure is useful in certain situations where applications are
36 only prepared to receive certain X events. After Tk_RestrictEvents is
37 called, Tk_DoOneEvent (and hence Tk_MainLoop) will filter X input
38 events through proc. Proc indicates whether a given event is to be
39 processed immediately, deferred until some later time (e.g. when the
40 event restriction is lifted), or discarded. Proc is a procedure with
41 arguments and result that match the type Tk_RestrictProc:
42 typedef Tk_RestrictAction Tk_RestrictProc(
43 ClientData clientData,
44 XEvent *eventPtr);
45 The clientData argument is a copy of the clientData passed to
46 Tk_RestrictEvents; it may be used to provide proc with information it
47 needs to filter events. The eventPtr points to an event under consid‐
48 eration. Proc returns a restrict action (enumerated type Tk_Restric‐
49 tAction) that indicates what Tk_DoOneEvent should do with the event.
50 If the return value is TK_PROCESS_EVENT, then the event will be handled
51 immediately. If the return value is TK_DEFER_EVENT, then the event
52 will be left on the event queue for later processing. If the return
53 value is TK_DISCARD_EVENT, then the event will be removed from the
54 event queue and discarded without being processed.
55 Tk_RestrictEvents uses its return value and prevClientDataPtr to return
57 information about the current event restriction procedure (a NULL
58 return value means there are currently no restrictions). These values
59 may be used to restore the previous restriction state when there is no
60 longer any need for the current restriction.
61 There are very few places where Tk_RestrictEvents is needed. In most
63 cases, the best way to restrict events is by changing the bindings with
64 the bind Tcl command or by calling Tk_CreateEventHandler and Tk_Dele‐
65 teEventHandler from C. The main place where Tk_RestrictEvents must be
66 used is when performing synchronous actions (for example, if you need
67 to wait for a particular event to occur on a particular window but you
68 don't want to invoke any handlers for any other events). The ``obvi‐
69 ous'' solution in these situations is to call XNextEvent or XWindow‐
70 Event, but these procedures cannot be used because Tk keeps its own
71 event queue that is separate from the X event queue. Instead, call
72 Tk_RestrictEvents to set up a filter, then call Tk_DoOneEvent to
73 retrieve the desired event(s).
74
76 delay, event, filter, restriction
77Tk Tk_RestrictEvents(3)