<HTML><HEAD><TITLE>Library Procedures - Tk_CreateEventHandler manual page</TITLE></HEAD><BODY> <H3><A NAME="M2">NAME</A></H3> Tk_CreateEventHandler, Tk_DeleteEventHandler - associate procedure callback with an X event <H3><A NAME="M3">SYNOPSIS</A></H3> <B>#include <tk.h></B><BR> <B>Tk_CreateEventHandler</B>(<I>tkwin, mask, proc, clientData</I>)<BR> <B>Tk_DeleteEventHandler</B>(<I>tkwin, mask, proc, clientData</I>)<BR> <H3><A NAME="M4">ARGUMENTS</A></H3> <DL> <P><DT>Tk_Window <B>tkwin</B> (in)<DD> Token for window in which events may occur. <P><DT>unsigned long <B>mask</B> (in)<DD> Bit-mask of events (such as <B>ButtonPressMask</B>) for which <I>proc</I> should be called. <P><DT>Tk_EventProc <B>*proc</B> (in)<DD> Procedure to invoke whenever an event in <I>mask</I> occurs in the window given by <I>tkwin</I>. <P><DT>ClientData <B>clientData</B> (in)<DD> Arbitrary one-word value to pass to <I>proc</I>. <P></DL> <H3><A NAME="M5">DESCRIPTION</A></H3> <B>Tk_CreateEventHandler</B> arranges for <I>proc</I> to be invoked in the future whenever one of the event types specified by <I>mask</I> occurs in the window specified by <I>tkwin</I>. The callback to <I>proc</I> will be made by <B><A HREF="../TkLib/HandleEvent.htm">Tk_HandleEvent</A></B>; this mechanism only works in programs that dispatch events through <B><A HREF="../TkLib/HandleEvent.htm">Tk_HandleEvent</A></B> (or through other Tk procedures that call <B><A HREF="../TkLib/HandleEvent.htm">Tk_HandleEvent</A></B>, such as <B>Tk_DoOneEvent</B> or <B><A HREF="../TkLib/MainLoop.htm">Tk_MainLoop</A></B>). <P> <I>Proc</I> should have arguments and result that match the type <B>Tk_EventProc</B>: <PRE>typedef void Tk_EventProc( ClientData <I>clientData</I>, XEvent *<I>eventPtr</I>);</PRE> The <I>clientData</I> parameter to <I>proc</I> is a copy of the <I>clientData</I> argument given to <B>Tk_CreateEventHandler</B> when the callback was created. Typically, <I>clientData</I> points to a data structure containing application-specific information about the window in which the event occurred. <I>EventPtr</I> is a pointer to the X event, which will be one of the ones specified in the <I>mask</I> argument to <B>Tk_CreateEventHandler</B>. <P> <B>Tk_DeleteEventHandler</B> may be called to delete a previously-created event handler: it deletes the first handler it finds that is associated with <I>tkwin</I> and matches the <I>mask</I>, <I>proc</I>, and <I>clientData</I> arguments. If no such handler exists, then <B>Tk_EventHandler</B> returns without doing anything. Although Tk supports it, it's probably a bad idea to have more than one callback with the same <I>mask</I>, <I>proc</I>, and <I>clientData</I> arguments. When a window is deleted all of its handlers will be deleted automatically; in this case there is no need to call <B>Tk_DeleteEventHandler</B>. <P> If multiple handlers are declared for the same type of X event on the same window, then the handlers will be invoked in the order they were created. <H3><A NAME="M6">KEYWORDS</A></H3> <A href="../Keywords/B.htm#bind">bind</A>, <A href="../Keywords/C.htm#callback">callback</A>, <A href="../Keywords/E.htm#event">event</A>, <A href="../Keywords/H.htm#handler">handler</A> <HR><PRE> <A HREF="../copyright.htm">Copyright</A> © 1990 The Regents of the University of California. <A HREF="../copyright.htm">Copyright</A> © 1994-1996 Sun Microsystems, Inc. <A HREF="../copyright.htm">Copyright</A> © 1995-1997 Roger E. Critchlow Jr.</PRE> </BODY></HTML>
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