Load and use a Glade layout in GTK2/C-CodePudding

I was trying to load a Glade layout into a GTK2 C code.

It consists of a window in which there is a VBox with 2 elements: a label and a button. I want to associate a signal to the button to close the application.

If I make all of this by using only C code it works fine, but when I load a layout I receive the following runtime error (the application starts but the button doesn't work):

(main:2581): GLib-GObject-WARNING **: 21:38:46.789: invalid (NULL) pointer instance

(main:2581): GLib-GObject-CRITICAL **: 21:38:46.790: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

Here the code I used, mylayout.glade is a file in my project folder:

#include <gtk/gtk.h>

void
end_program (GtkWidget * wid, gpointer ptr)
{
    gtk_main_quit();
    
    return;
}

int
main (int argc, char * argv[])
{
    GError * error = NULL;
    
    gtk_init(&argc, &argv);
    
    GtkBuilder * builder = gtk_builder_new();
    
    if (0 == gtk_builder_add_from_file(builder, "mylayout.glade",
                                       &error))
    {
      g_printerr("Error loading file: %s\n", error->message);
      g_clear_error(&error);
      
      return 1;
    }

    GtkWidget * win = (GtkWidget *) gtk_builder_get_object(builder,
                                                           "window1");
    GtkWidget * btn = (GtkWidget *) gtk_builder_get_object(builder,
                                                           "button1");
    
    g_signal_connect(btn, "clicked", G_CALLBACK(end_program), NULL);
                                                           
    gtk_widget_show_all(win);
    gtk_main();
    
    return 0;
}

The only thing I noticed is that if I remove the g_signal_connect() line the error disappear.

Any help is really appreciated.

CodePudding user response：

You might want to check the name you gave your button widget in the glade file. The only way I could replicate your error was when the name of the button widget defined in the glade file was something different from "button1" as referenced in the program statement:

GtkWidget * btn = (GtkWidget *) gtk_builder_get_object(builder, "button1");

When the glade file had a different name for the button (e.g. "button" or "btn"), then I received the identical warning and critical error message as you noted.

Regards.