Gtk3 quit application from a menu item fails

Im trying to

call g_application_quit from a menu item to quit the application same as the x button
using signal connect :

g_signal_connect(quitMi, "activate", G_CALLBACK(g_application_quit),G_APPLICATION(app));

but I get the following message and application stays open

message

(quit:XXX): GLib-GIO-CRITICAL **: 09:59:42.547: g_application_quit: assertion 'G_IS_APPLICATION (application)' failed

code

#include <gtk/gtk.h>

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

  GtkWidget *menubar;
  GtkWidget *fileMenu;
  GtkWidget *fileMi;
  GtkWidget *quitMi;

  window = gtk_application_window_new (app);
  gtk_window_set_title (GTK_WINDOW (window), "chesstrainer");

  gtk_container_set_border_width (GTK_CONTAINER (window), 0);

  vbox = gtk_vbox_new(FALSE, 0);
  gtk_container_add (GTK_CONTAINER (window), vbox);

  menubar = gtk_menu_bar_new();
  fileMenu = gtk_menu_new();
  fileMi = gtk_menu_item_new_with_label("File");
  quitMi = gtk_menu_item_new_with_label("Quit");

  gtk_menu_item_set_submenu(GTK_MENU_ITEM(fileMi), fileMenu);
  gtk_menu_shell_append(GTK_MENU_SHELL(fileMenu), quitMi);
  gtk_menu_shell_append(GTK_MENU_SHELL(menubar), fileMi);
  gtk_box_pack_start(GTK_BOX(vbox), menubar, FALSE, FALSE, 0);

  frame = gtk_frame_new (NULL);
  gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_IN);
//  gtk_container_add (GTK_CONTAINER (window), frame);
  gtk_container_add (GTK_CONTAINER (vbox), frame);
  g_signal_connect(quitMi, "activate",
      G_CALLBACK(g_application_quit),G_APPLICATION(app));

  drawing_area = gtk_drawing_area_new ();
  /* set a minimum size */
  gtk_widget_set_size_request (drawing_area, 800, 800);

  gtk_container_add (GTK_CONTAINER (frame), drawing_area);

  gtk_widget_show_all (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;
}

How can I properly close the application from the quit menu item ?

Solution

If you read the documentation, the activate signal for a GtkMenuItem requires a callback with the signature void (*)(GtkMenuItem *mi, gpointer userdata).

You are passing in g_application_quit, which has a signature of void (*)(GApplication *).

Hence the error message, indicating the the argument to g_application_quit is not a GApplication *, since it is receiving a GtkMenuItem *.

You need to write a callback for the activate signal, and have it call g_application_quit.