gtk.rb

require 'gtk3'

button = Gtk::Button.new("Hello World")
button.signal_connect("clicked") {
  puts "Hello World"
}

window = Gtk::Window.new
window.signal_connect("delete_event") {
  puts "delete event occurred"
  #true
  false
}

window.signal_connect("destroy") {
  puts "destroy event occurred"
  Gtk.main_quit
}

window.border_width = 10
window.add(button)
window.show_all

Gtk.main