Using GTK4 to build a small window app

Once the small program is compiled, I run it by double clicking the executable in Nautilus. When I have a second but completely different windowed app and double click on it while the first windowed program is running, the result is that the first program is started for a second instance rather than a new instance of the different program.

Program 1:

#include <gtk/gtk.h>

//gcc $( pkg-config --cflags gtk4 ) -o example-0 example-0.c $( pkg-config --libs gtk4 ) -lGL -g

static void activate(GtkApplication* app, gpointer user_data)
{
  GtkWidget *window;

  window = gtk_application_window_new (app);
  gtk_window_set_title (GTK_WINDOW (window), "Window");
  gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);
  gtk_widget_show (window);
}

int main(int argc, char **argv)
{
  GtkApplication *app;
  int status;

  app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

    printf("EXITING\n");
  return status;
}

Program 2:

//gcc $( pkg-config --cflags gtk4 ) -o example-1 example-1.c $( pkg-config --libs gtk4 ) 
#include <gtk/gtk.h>

static void
print_hello (GtkWidget *widget,
             gpointer   data)
{
  g_print ("Hello World\n");
}

static void
activate (GtkApplication *app,
          gpointer        user_data)
{
  GtkWidget *window;
  GtkWidget *button;
  GtkWidget *box;

  window = gtk_application_window_new (app);
  gtk_window_set_title (GTK_WINDOW (window), "Window");
  gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);

  box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 0);
  gtk_widget_set_halign (box, GTK_ALIGN_CENTER);
  gtk_widget_set_valign (box, GTK_ALIGN_CENTER);

  gtk_window_set_child (GTK_WINDOW (window), box);

  button = gtk_button_new_with_label ("Hello World");

  g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);
  g_signal_connect_swapped (button, "clicked", G_CALLBACK (gtk_window_destroy), window);

  gtk_box_append (GTK_BOX (box), button);

  gtk_widget_show (window);
}

int
main (int    argc,
      char **argv)
{
  GtkApplication *app;
  int status;

  app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

  return status;
}

I cannot figure out why. Has anybody else ever ran across this problem? I should be easily reproducible.

I am on Ubuntu 22.04.2 LTS I have GTK v4 and the following compiler version:

$ gcc --version
gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0

also using Wayland.

Thanks, Jaye

Two different GTK applications should have two different application_id. For example org.gtk.example1 and org.gtk.example2 in the gtk_application_new() instruction.

See https://docs.gtk.org/gio/type_func.Application.id_is_valid.html