Up North

I ran into a slight problem when I tried to create a type registered subclass in Ruby/GTK+. This is done by adding type_register in your class definition. This worked fine until I tried to pass arguments to the super class constructor through the super() call.

In my previous example, I passed the arguments like usual to the super call. It turns out that when you have registered your class with the GObject type system (which I didn’t do in that example) it overloads the super() call and you need to pass the arguments as a hash instead.

Here is an example subclassing Gtk::Button that sets the button up defaulting to underline mnemonics.

require 'gtk2'

class MyButton < Gtk::Button
  type_register

  def initialize(label)
    super({:label => label, :use_underline => true})
  end

  def signal_do_clicked(*args)
    puts “Clicked”
  end
end

w = Gtk::Window.new

b = MyButton.new(”My _Button”)
w.add(b)

w.signal_connect(:delete_event) do
  Gtk.main_quit
end

w.show_all
Gtk.main

Kudos to Kou for showing how to do it.

Davyd is spot on when bringing up the use of subclassing in GTK+. This is a step that comes natural for most people used to OO programming but (probably due to having to write a lot of boiler plate code) often is neglected by GTK+ application developers.

While many feel it’s daunting to subclass GTK+ widgets in C, it can be really nice when writing applications in other languages. Just like Davyd showed, Python is such a language, so is Ruby which I will show a similar brief example of here for those that are trying to get into Ruby/GTK+.

require 'gtk2'

# Defining OpenFileDialog
class OpenFileDialog < Gtk::FileChooserDialog
  @@CWD = nil

  def initialize(parent_window)
    super("Open file", parent_window,
          Gtk::FileChooser::ACTION_OPEN, nil,
          [Gtk::Stock::CANCEL, Gtk::Dialog::RESPONSE_CANCEL],
          [Gtk::Stock::OPEN, Gtk::Dialog::RESPONSE_OK])

    self.default_response = Gtk::Dialog::RESPONSE_OK

    self.current_folder = @@CWD unless @@CWD.nil?

    signal_connect :response do |dialog, response|
      @@CWD = self.current_folder if response == Gtk::Dialog::RESPONSE_OK
    end
  end
end

# Using OpenFileDialog
2.times do
  d = OpenFileDialog.new(nil)

  d.run do |response|
    puts "filename = #{d.filename}" if response == Gtk::Dialog::RESPONSE_OK
  end

  d.destroy
end

The second half simply to try it out. For a nicer paste, see http://pastie.caboo.se/148847.

But it’s so hard in C!
Writing all the boilerplate by hand is a lot of work and error prone. However, here are two tips for making life easier.

The first way is to implement a dummy object that you later copy and query/replace. A nice tool for using this method is Regexxer) that lets you easily change the dummy name into your object name. I suggest you hook up your dummy object in the Makefile in order to make sure it always builds.

The other solution is to use a generator script such as Spuug to generate all the boilerplate for you. It makes it very easy to create new subclasses when you need them.

Update: As Johannes pointed out in a comment, Anjuta also comes with a generator for subclassing.

I’ve had this problem since I got the X61 that the screen is almost black after coming back from suspended mode in Ubuntu. The problem can be solved by switching to terminal and then back to X but today I found a solution in the Ubuntu Forums which solves the problem.

Much kudos to lbharti for sharing this very simple solution.

Edit your /etc/default/acpi-support and set DOUBLE_CONSOLE_SWITCH=true