GTK+ Forums

TriKri · Familiar Face Joined: 19 Mar 2008 Posts: 19

What's the different between delete_event and destroy for a windows? Also, what is the difference between g_signal_connect and g_signal_connect_swap? Thanks in advance.

dreblen · Posted: Sat Mar 22, 2008 8:22 pm Post subject:

I can't seem to find the delete-event anywhere, so I can't help with that,
but for the difference between g_signal_connect and g_signal_connect_swapped, you can look at these pages:
http://library.gnome.org/devel/gobject/stable/gobject-Signals.html#g-signal-connect
http://library.gnome.org/devel/gobject/stable/gobject-Signals.html#g-signal-connect-swapped
Hope that these help

TriKri · Familiar Face Joined: 19 Mar 2008 Posts: 19

Thanks! But I didn't understand what they ment with their explanaition of g_signal_connect_swapped(). By the way, I found the delete event in their tutorial: http://library.gnome.org/devel/gtk-tutorial/stable/c39.html. It seems that the delete_event is something that is triggered by the user, while the destroy_event is triggered by something the program itself has done, like trying to destroy the window from within the program, or allowing the program to shut down from within the handel of delete_event.

dreblen · Posted: Sun Mar 23, 2008 8:16 pm Post subject:

my understanding of of g_signal_connect_swapped() is that the object that is calling it is passed as the argument to the callback function instead of the data argument.

as far as finding the delete_event, what I meant was something like this:
http://library.gnome.org/devel/gtk/stable/GtkWidget.html#GtkWidget-destroy-event

Micah Carrick · Posted: Mon Mar 24, 2008 1:26 pm Post subject:

The swapped function allows you to swap the order of the arguments that are passed to the callback function. For example, if you have a GtkButton which will destroy the GtkWindow you would attach a callback function to the "clicked" signal. The callback for the "clicked" callback function is defined in the manual as:

Code: (C)
1 2	void user_function (GtkButton *button, gpointer user_data)

This tells us that when the GtkButton is clicked, the callback function we connect will recieve the GtkButton object first, and our user_data second. This is what would happen if we used g_signal_connect ().

However, if we want to attach a callback function in which the FIRST argument is the user_data, then we use g_signal_connect_swapped (). This allows us to use some already written functions as callbacks such as gtk_widget_destroy ().

Example 1: Without using swapped

Code: (C)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21	void my_destroy_callback (GtkButton button, gpointer user_data) { / destroy the window / gtk_widget_destroy (GTK_WIDGET (user_data)); } int main() { GtkWidget button; GtkWidget window; / create and pack widgets here ... */ g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (my_destroy_callback), (gpointer)window); gtk_main(); return 0; }

Example 2: Swapping Arguments

Code: (C)
1 2 3 4 5 6 7 8 9 10 11 12 13 14	int main() { GtkWidget button; GtkWidget window; /* create and pack widgets here ... */ g_signal_connect_swapped (G_OBJECT (button), "clicked", G_CALLBACK (gtk_widget_destroy), (gpointer)window); gtk_main(); return 0; }

As for the delete-event and destroy events, they have different uses. The delete event occurs when the GtkObject is destroyed. You might use this to cleanup other objects. The delete-event occurs when the GtkWindow is requested to be deleted (user clicks the 'x' for example) and you can stop the delete event from propagating based on your return value. This is often used to prompt people to save their work or confirm they really want to quit. Check out this example: Confirm Quit Dialog on "delete-event" signal

cadcrazy · Joined: 12 Jun 2008 Posts: 2

Thanks Micah Carrick for such a nice explanation.
I have one confusion. What benefit we will get if we pass user data first to library functions like gtk_widget_destroy() through g_signal_connect_swapped() over usual g_signal_connect() call to same function( as i guess we can also call gtk_widget_destroy() throgh g_signal_connect() )

Sorry for noobish question :D

dreblen · Posted: Fri Jun 13, 2008 2:57 pm Post subject:

if you use g_signal_connect to connect to something like gtk_widget_destroy,
it will pass the signal object to the function, whereas _swapped will pass your data to the function
ex:

Code: (C)
1 2 3 4	/* this will delete 'button' on its clicked signal, even though we're passing 'other_widget' as user_data / g_signal_connect(G_OBJECT(button), "clicked", G_CALLBACK(gtk_widget_destroy), (gpointer)other_widget); / this will delete 'other_widget' on button's clicked signal */ g_signal_connect_swapped(G_OBJECT(button), "clicked", G_CALLBACK(gtk_widget_destroy), (gpointer)other_widget);