Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!seismo!hal!nancie
From: nancie@hal.CSS.GOV (Nancie Matson)
Newsgroups: comp.windows.x
Subject: Event Loops (Using XtMainLoop and XtNextEvent)
Message-ID: <452@hal.CSS.GOV>
Date: 30 Aug 90 14:19:39 GMT
Reply-To: nancie@hal.css.gov (Nancie Matson)
Organization: ENSCO Inc., Melbourne FL
Lines: 63


I am trying to implement an event loop in my Xt application,
(in addition to XtMainLoop) to capture input from a list
of popup toggle widgets.  I am using XtNextEvent to retrieve
the next event on the queue, and them I am testing it to
see if it is one of the widgets I am looking for.

The problem I get occurs before the Event Loop is 
executed.  Whatever I try to do  immediately before
this EventLoop, doesn't get executed.   For example, if
I want to display a message to the user by changing
a label widget, and then execute the Event Loop, I never
see the message on the screen.

I know this has to do with the server not recieving the last
event on the queue (XtMainLoop's queue), but I tried using
XFlush, and XSync before executing my event loop with no
luck.  

The following is a sample of my event Loop.

-------
       strcpy(label,"Select an Event with the mouse.");
       XtSetArg (args[0],XtNlabel,label);
       XtSetValues(status,args,1);

       while (!done)
       {
          XtNextEvent(&event);
          if (event.type == ButtonPress)
          {
             if (((event.xbutton.button == Button1) ||
                  (event.xbutton.button == Button2) ||
                  (event.xbutton.button == Button3)) &&
                  (event.xbutton.window == XtWindow(evnt.data[j].esym)))
             {
                point = Project (1,map.proj->id,evnt.data[j].loc,0);
                loc->x = (int)point.xlon;
                loc->y = (int)point.ylat;
                done = 1;
                *index = j;
             }
          }
       }
       strcpy(label,"Mouse Ready ...");
       XtSetArg (args[0],XtNlabel,label);
       XtSetValues(status,args,1);

----------

The first call to XtSetValues doesn't appear on the screen, but the second
one does.  Is there any way to ensure that events/server requests placed
on the queue before a call to XtNextEvent get executed?

Any info would be helpful.  SO far I've tried using XtFlush, XtSync and
even XtDispatchEvent.

Please e-mail to nancie@hal.CSS.GOV.  I will post a summary if anyone
is interested.

-Nancie P. Matson
 ENSCO, Inc.
 nancie@hal.CSS.GOV