Callback if a gtkwidget gets destroyed

[chakka.lokesh (Lokesh Venkata Kumar Chakka)]

Is it possible to have a callback if any widget get is getting destroyed.
In the following code, for example, I want the callback to be executed if spin button is getting destroyed.

#include <gtk/gtk.h>
#include <math.h>

gboolean destroy_callback( GtkWidget *spin_button, void *array )
{
	printf( "%s %d freeing: %p\n", __func__, __LINE__, array );
	free( array );
	return TRUE;
}

int main()
{
	gtk_init( NULL, NULL );
 	GtkWidget *const window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
 	gtk_window_set_default_size( GTK_WINDOW(window), 100, 100 );
 	g_signal_connect( window, "destroy", G_CALLBACK(gtk_main_quit), NULL );
 	GtkWidget *box = gtk_box_new( GTK_ORIENTATION_VERTICAL, 5 );
 
 	gtk_container_add( (GtkContainer*)window, box );
 	int *array = calloc( 10, 10 );
 	GtkWidget *spin = gtk_spin_button_new_with_range( 0, 255, 1 );
 	gtk_box_pack_start( (GtkBox*)box, spin, FALSE, FALSE, 5 );
 	if( g_signal_connect( G_OBJECT( box ), "delete-event", G_CALLBACK(destroy_callback), array ) == 0 )
 	{
 		fprintf( stderr, "%s %d Unable to connect", __func__, __LINE__ );
 		return 0;
 	}
 	gtk_widget_show_all( window );
 	gtk_main();
 	return 0;
 }

[ebassi (Emmanuele Bassi)]

The GtkWidget::delete-event signal is only emitted on top levels, not widgets.

If you want to associate some data to a widget and free it when the widget is destroyed, you have two options:

1. use the GtkWidget::destroy signal, connect a callback to it, and free the data; this is similar to what you did above
2. use g_object_set_data_full() to store the data on the widget instance, and have it freed when the object is finalized, e.g.:

  // Your use of calloc() is wrong; the second argument is the size of each element
  int *int_array = calloc (10, sizeof (int));
  g_object_set_data_full (G_OBJECT (spin),
                          "spin-data-array",
                          int_array,
                          (GDestroyNotify) free);

you can retrieve the data pointer from the instance using g_object_get_data().

[chakka.lokesh (Lokesh Venkata Kumar Chakka)]

i have modified the code as follows:

#include <gtk/gtk.h>
#include <math.h>

gboolean destroy_callback( GtkWidget *widget, void *array )
{
printf( “%s %d freeing: %p\n”, __func__, __LINE__, array );
free( array );
return TRUE;
}

int main()
{
gtk_init( NULL, NULL );
GtkWidget *const window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
gtk_window_set_default_size( GTK_WINDOW(window), 100, 100 );
g_signal_connect( window, “destroy”, G_CALLBACK(gtk_main_quit), NULL );
GtkWidget *box = gtk_box_new( GTK_ORIENTATION_VERTICAL, 5 );

gtk_container_add( (GtkContainer*)window, box );
int *array = calloc( 10, sizeof(int) );
GtkWidget spin = gtk_spin_button_new_with_range( 0, 255, 1 );
gtk_box_pack_start( (GtkBox)box, spin, FALSE, FALSE, 5 );
if( g_signal_connect( G_OBJECT( box ), “destory”, G_CALLBACK(destroy_callback), array ) == 0 )
{
fprintf( stderr, “%s %d Unable to connect\n”, __func__, __LINE__ );
return 0;
}
gtk_widget_show_all( window );
gtk_main();
return 0;
}

I am seeing error output :

$ gcc destroy.c `pkg-config --cflags --libs gtk±3.0 glib-2.0` && ./a.out

(a.out:13235): GLib-GObject-WARNING **: 10:04:52.312: …/…/…/gobject/gsignal.c:2617: signal ‘destory’ is invalid for instance ‘0x55fa2a7341a0’ of type ‘GtkBox’
main 25 Unable to connect

[ebassi (Emmanuele Bassi)]

The signal is called “destroy”, not “destory “.