Implementing custom widget

["Germán Diago" <germandiago gmail com>]

Hello. I'm trying to implement a custom widget following the gtkmm
book tutorial.

My widget is a made of a Gtk::VBox-derived widget and a
Gtk::Widget-derived widget, which shows a set of images one above the
other.
I need to move the images in my widget, so I create a Gdk::Window for
my widget, since it is needed to catch events, I think.
The VBox contains some Gtk::CheckBoxes and a Widget-derived widget (my
own custom widget).

The problem is that I pack_start(mycustomwidget) and then pack_start
the checkbuttons in my container, but the space allocated
for the custom widget is not considered when packing the checkboxes,
so when the application starts it hides the customwidget.
How can I make the space allocated by the widget to be considered by
the VBox-derived widget? Thanks in advance.