gistfile1.rb

#!/usr/bin/env ruby
require 'ffi-gtk3'

class Aplicacao
  def initialize
    @app = Gtk::Application.new 'ruby.jedi', 0
    @janela = []

    GObject.signal_connect(@app, "activate", nil) do
      @janela.each{ |e| e.present }
    end
    GObject.signal_connect(@app, "startup", nil) do
      constroi_ui
    end
  end

  def constroi_ui
    cria_menu
    @janela.push Gtk::ApplicationWindow.new @app
    @janela.each { |e| e.show }
  end

  def cria_menu
    quit_action = Gio::SimpleAction.new "quit", nil
    GObject.signal_connect(quit_action, "activate", nil) { @app.quit }
    @app.add_action quit_action

    new_window_action = Gio::SimpleAction.new "nova", nil
    GObject.signal_connect(new_window_action, "activate", nil) do
      @janela.push Gtk::ApplicationWindow.new @app
      @janela.last.show
    end
    @app.add_action new_window_action

    menu = Gio::Menu.new

    edit = Gio::Menu.new
    secao = Gio::MenuItem.new_section "Editar", edit
    edit.append "Nova janela", "app.nova"
    menu.append_submenu "Editar", edit
    sair = Gio::MenuItem.new "Sair daqui", "app.quit"
    menu.append_item sair

    @app.set_app_menu(menu)
  end

  def run
    @app.run nil
  end

end

aplicacao = Aplicacao.new
aplicacao.run