NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/comp/windows/openloo/4567

Internet Message Format | 1992-11-18 | 2.0 KB

Path: sparky!uunet!ittc!dscott
From: [e-mail] (Dave Scott)
Newsgroups: comp.windows.open-look
Subject: Re: Problem with XV_KEY_DATA
Message-ID: <[e-mail]>
Date: 18 Nov 92 21:05:37 GMT
References: <[e-mail]>
Sender: [e-mail]
Organization: Westinghouse - Simulators Division, Pittsburgh, PA
Lines: 52
In-reply-to: [e-mail]'s message of 17 Nov 92 17:37:08 GMT


In article <[e-mail]> [e-mail] (John Collins) writes:

=>I have been writing an application with XView3.  It seems that
=>there is a problem with XV_KEY_DATA.  My application creates a canvas
=>with an XV_KEY_DATA field named CANVAS_XIMAGE_KEY.  A button callback
=>procedure (new_ximage()) changes the CANVAS_XIMAGE_KEY by calling a
=>routine called make_canvas_ximage() (which returns an XImage *).  This
=>is the code

=>void
=>new_ximage(item, event)
=>Panel_item item;
=>Event  *event;
=>{
=>   /* First remove the old ximage key. */
=>   xv_set(canvas, XV_KEY_DATA_REMOVE, CANVAS_XIMAGE_KEY);

=>   /* Get the new XImage and attach it to the canvas. */
=>   xv_set(canvas, XV_KEY_DATA, CANVAS_XIMAGE_KEY, make_canvas_ximage() );

=>   /* redisplay */
=>   ...
=>}

=>The wierd thing about this code is that sometimes it goes off without a
=>hitch, and sometimes it makes the program crash.  The crash always happens
=>when the routine make_canvas_ximage returns.

Ahhhh!  The key lies in the above statement that it works "sometimes."

Try changing the line:

  xv_set(canvas, XV_KEY_DATA_REMOVE, CANVAS_XIMAGE_KEY);

to:

  xv_set(canvas, XV_KEY_DATA_REMOVE, CANVAS_XIMAGE_KEY, NULL);

Same change for the other xv_set().

The NULL at the end of the xv_set() call will get you every time (er,
well, sometimes :-).

Shalom,

-dave

--
 David A. Scott - [e-mail]   -OR-   [e-mail] (Westinghouse)
 interLogic Software, Inc.             "The shortest distance between
 (Currently on loan to Westinghouse)      two points is under construction."