Path: utzoo!attcan!uunet!ginosko!usc!bloom-beacon!EXPO.LCS.MIT.EDU!kit
From: kit@EXPO.LCS.MIT.EDU (Chris D. Peterson)
Newsgroups: comp.windows.x
Subject: Re: Changing label
Message-ID: <8908282229.AA01895@expo.lcs.mit.edu>
Date: 28 Aug 89 22:29:38 GMT
References: <4344@cps3xx.UUCP>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 94



> I think XFlush() must be treated differently from other requests (doesn't have 
> to go the the buffer), because if it does then how can it flush the buffer ?

It turns out that not only must the X buffer be flushed, but the toolkit needs
to dispatch an expose event to the label widget.  The means that a simple
call to XFlush() will not do the trick.

> Any other suggestion ?

You bet!  Here is a short example program that seems to work correctly.
Please keep in mind that any kind of event dispatching and blocking like
this is at best a bit kludgy, and at worst very dangerous.  I do not suggest
using code that blocks, but if you must here is an example.  You will notice
that I have put in a fail safe so that if the event never comes you will not
end up with a frozen application.  

						Chris D. Peterson     
						MIT X Consortium 

Net:	 kit@expo.lcs.mit.edu
Phone:   (617) 253 - 9608	
Address: MIT - Room NE43-213

------------------ cut here ----------------------------------------------

#include <stdio.h>

#include <X11/Intrinsic.h>
#include <X11/StringDefs.h>

#include <X11/Box.h>
#include <X11/Command.h>
#include <X11/Label.h>

#define DELAY 1000		/* This value seems to work for my
				   network, your mileage may vary. */
void
ChangeLabel(w, str)
Widget w;
char * str;
{
  Arg args[1];
  XEvent event;
  int count;
  
  XtSetArg(args[0], XtNlabel, str);
  XtSetValues(w, args, (Cardinal) 1);
  while ( (count < DELAY) &&
	 !XCheckTypedWindowEvent(XtDisplay(w), XtWindow(w), Expose, &event) )
    count++;			/* Keeps the application from seizing up
				   if the window isn't visable. */

  XtDispatchEvent( &event );
  XFlush(XtDisplay(w));
  sleep(5);
}

/* ARGSUSED */
void 
Activate(w, closure, call_data)
Widget w;
caddr_t closure, call_data;
{
  ChangeLabel((Widget) closure, "one");
  ChangeLabel((Widget) closure, "two");
  ChangeLabel((Widget) closure, "three");
  printf("Done.\n");
}

void 
main(argc, argv)
int argc;
char **argv;
{
    Widget toplevel, box, command, label;

    toplevel = XtInitialize( NULL, "Demo", NULL, (Cardinal) 0, &argc, argv );

    box = XtCreateManagedWidget( "box", boxWidgetClass, toplevel,
				NULL, (Cardinal) 0);

    label = XtCreateManagedWidget( "label", labelWidgetClass, box,
				    NULL, (Cardinal) 0);

    command = XtCreateManagedWidget( "command", commandWidgetClass, box,
				    NULL, (Cardinal) 0);

    XtAddCallback(command, XtNcallback, Activate, (caddr_t) label);
    
    XtRealizeWidget(toplevel);
    XtMainLoop();
}