We recommand the following documents. Most of them were written with C in mind, but should be easily adapted after you’ve read the rest of this document.
 “Gtk+/Gome Application Development” – Havoc Pennington This book, by one of the main authors of the the GNOME environment, describes in detail some of the inner mechanisms of gtk+, including signal handling, and a complete description of all the widgets and all the events found in Gdk.Event.
It is worth noting that this book has been published under the Open Publication License. You can get an electronic copy of it at http://www.opencontent.org/.