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From: jlf@earth.cray.COM (John Freeman)
Newsgroups: comp.windows.x
Subject: Application Context
Message-ID: <8902071640.AA05010@thelake.cray.com>
Date: 7 Feb 89 16:40:53 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 59

I'm trying to put together some examples for a class I'm
teaching on Toolkit programming.  I want to discuss 
application contexts, but don't quite understand their use
and meaning.  Could someone give me a definition?

The one example I'm trying to work out is to use application
contexts to do "Hello, World" on two displays, using the
toolkit.  As a preliminary step, I rewrote the now famous
hw.c to use XtToolkitInitialize() and XtCreateApplicationContext(),
and it doesn't work.  The code below demonstrates the problem.
If I pass a NULL pointer to XtOpenDisplay as the Application
Context parameter, it works.  If I pass the real XtAppContext
returned from the XtCreateApplicationContext(), the program
never displays anything - it goes into XtMainLoop(), but 
nothing happens.


#include <X11/Xlib.h>
#include <X11/Intrinsic.h>
#include <X11/StringDefs.h>
#include <X11/Shell.h>
#include <X11/Label.h>
#include <stdio.h>
#define STRING "Hello, World!"

Arg label_args[] = {XtNlabel, (XtArgVal) STRING };
Arg argies[5];

main(argc,argv)
int argc;
char **argv;
{
    Widget toplevel, label1, label2;
    Display *d1p, *d2p;
    XtAppContext app1, app2;

    XtToolkitInitialize();
    app1 = XtCreateApplicationContext();

/**** This works ****/
    d1p = XtOpenDisplay(NULL, NULL, NULL, "Xlabel", NULL, 0, &argc, argv);
#if 0
/**** This doesn't ****/
    d1p = XtOpenDisplay(app1, NULL, NULL, "Xlabel", NULL, 0, &argc, argv);
#endif
    if (d1p == NULL) { printf("XtOpenDisplay failed\n"); return; }

    argies[0].name = XtNscreen;
    argies[0].value = (XtArgVal) DefaultScreenOfDisplay(d1p);
    toplevel = XtAppCreateShell("XShell", "xshell",
	applicationShellWidgetClass, d1p, argies, 1);

    label1 = XtCreateWidget(argv[0], labelWidgetClass,
	    toplevel, label_args, XtNumber(label_args));

    XtManageChild(label1);
    XtRealizeWidget(toplevel);
    XtMainLoop();
}