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markom |
'\"
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'\" Copyright (c) 1990 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" RCS: @(#) $Id: EventHndlr.3,v 1.1.1.1 2002-01-16 10:25:48 markom Exp $
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'\"
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.so man.macros
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.TH Tk_CreateEventHandler 3 "" Tk "Tk Library Procedures"
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.BS
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.SH NAME
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Tk_CreateEventHandler, Tk_DeleteEventHandler \- associate procedure callback with an X event
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.SH SYNOPSIS
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.nf
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\fB#include \fR
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.sp
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\fBTk_CreateEventHandler\fR(\fItkwin, mask, proc, clientData\fR)
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.sp
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\fBTk_DeleteEventHandler\fR(\fItkwin, mask, proc, clientData\fR)
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.SH ARGUMENTS
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.AS "unsigned long" clientData
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.AP Tk_Window tkwin in
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Token for window in which events may occur.
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.AP "unsigned long" mask in
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Bit-mask of events (such as \fBButtonPressMask\fR)
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for which \fIproc\fR should be called.
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.AP Tk_EventProc *proc in
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Procedure to invoke whenever an event in \fImask\fR occurs
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in the window given by \fItkwin\fR.
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.AP ClientData clientData in
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Arbitrary one-word value to pass to \fIproc\fR.
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.BE
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.SH DESCRIPTION
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.PP
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\fBTk_CreateEventHandler\fR arranges for \fIproc\fR to be
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invoked in the future whenever one of the event types specified
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by \fImask\fR occurs in the window specified by \fItkwin\fR.
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The callback to \fIproc\fR will be made by \fBTk_HandleEvent\fR;
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this mechanism only works in programs that dispatch events
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through \fBTk_HandleEvent\fR (or through other Tk procedures that
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call \fBTk_HandleEvent\fR, such as \fBTk_DoOneEvent\fR or
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\fBTk_MainLoop\fR).
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.PP
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\fIProc\fR should have arguments and result that match the
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type \fBTk_EventProc\fR:
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.CS
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typedef void Tk_EventProc(
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ClientData \fIclientData\fR,
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XEvent *\fIeventPtr\fR);
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.CE
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The \fIclientData\fR parameter to \fIproc\fR is a copy of the \fIclientData\fR
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argument given to \fBTk_CreateEventHandler\fR when the callback
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was created. Typically, \fIclientData\fR points to a data
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structure containing application-specific information about
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the window in which the event occurred. \fIEventPtr\fR is
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a pointer to the X event, which will be one of the ones
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specified in the \fImask\fR argument to \fBTk_CreateEventHandler\fR.
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.PP
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\fBTk_DeleteEventHandler\fR may be called to delete a
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previously-created event handler: it deletes the first handler
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it finds that is associated with \fItkwin\fR and matches the
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\fImask\fR, \fIproc\fR, and \fIclientData\fR arguments. If
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no such handler exists, then \fBTk_EventHandler\fR returns
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without doing anything. Although Tk supports it, it's probably
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a bad idea to have more than one callback with the same \fImask\fR,
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\fIproc\fR, and \fIclientData\fR arguments.
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When a window is deleted all of its handlers will be deleted
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automatically; in this case there is no need to call
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\fBTk_DeleteEventHandler\fR.
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.PP
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If multiple handlers are declared for the same type of X event
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on the same window, then the handlers will be invoked in the
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order they were created.
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.SH KEYWORDS
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bind, callback, event, handler
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