Control Closing of Gtk::Dialog

[Jon Black <juan black gmail com>]

I have a simple Gtk::Dialog with 3 text entry fields, a cancel button, and an ok button. I'd like the dialog to close whenever the user presses cancel, and when the user presses ok only if all the text entry fields contain text. It seems that by default, the dialog closes when either button is pressed. If I connect the buttons to a handler, there seems to be no way to prevent the closing from happening. So, how can I control whether the dialog closes when the ok button is pressed?