How to create a custom signal in Ruby-GTK2 I'm playing with the GTK2 bindings for Ruby. When coding GUI things, I usually like to build my own higher level widgets by subclassing containers and populating them with other widgets. For example, I'm creating an image browser and I like to make an ImageList class that subclasses a Gtk::ScrolledWindow and builds the TreeView inside it:

class ImageList < Gtk::ScrolledWindow
      def initialize
              super
              @files = Gtk::ListStore.new(String, String, Gdk::Pixbuf)
              @fileList = Gtk::TreeView.new(@files)
              renderer = Gtk::CellRendererPixbuf.new
              col = Gtk::TreeViewColumn.new("Thumb", renderer, :pixbuf => 2)
              @fileList.append_column(col)
              renderer = Gtk::CellRendererText.new
              col = Gtk::TreeViewColumn.new("File name", renderer, :text => 1)
              @fileList.append_column(col)
              self.add @fileList
      end
      
      def readDir (root)
              Dir.foreach root do  dir 
                      file = root+'/'+dir
                      if !FileTest.directory?(file) && dir =~ /\.jpe?g$/ && FileTest.readable?(file)
                              thumb = getThumbnail(file)
                              iter = @files.append
                              iter[0] = file
                              iter[1] = dir
                              iter[2] = Gdk::Pixbuf.new thumb
                              File.delete(thumb)
                      end
              end
      end
end

When working like this, I find myself very soon in need of creating custom signals: in this case I want to make a signal that ImageList emits when the user select an image from the TreeView, like this:

fileList.signal_connect("selected") do  filename 
      imageDetails.load(filename)
end

Now, how do I implement that extra 'selected' signal in my ImageList? Ruby documentation is usually very good and easy to find, but this time Google had little to say to me. When the going gets tough, the tough gets to IRC:

enrico> Hi.  http://ruby-gnome2.sourceforge.jp/?News_20031116_1 says that it is
        possible to create custom signals, however I could not find any
        documentation on how to do it.  Anyone has a link or a short explanation?
pterjan> glib/sample in the source IIRC
pterjan>   # define new signal "hoge"
pterjan>   signal_new("hoge",                  # name
pterjan>              GLib::Signal::RUN_FIRST, # flags
pterjan>              nil,                     # accumulator (XXX: not supported yet)
pterjan>              nil,                     # return type (void == nil)
pterjan>              Integer, Integer         # parameter types
pterjan>              )
pterjan> in glib/sample/type-register.rb
enrico> ooh!
enrico> pterjan: thanks!
enrico> I'll blog about it, it might make it easier for others to google this answer

Thanks pterjan, and oh, coolness! So there are nice examples that I was silly enough to miss. Are they included in the Debian packages? Oh, yes! Right in /usr/share/doc/libglib2-ruby/examples/type-register.rb. Here's the ImageList class with the new signal:

class ImageList < Gtk::ScrolledWindow
      type_register
      signal_new("selected",              # name
                 GLib::Signal::RUN_FIRST, # flags
                 nil,                     # accumulator (XXX: not supported yet)
                 nil,                     # return type (void == nil)
                 String                   # parameter types
                 )
      def initialize
              super
              @files = Gtk::ListStore.new(String, String, Gdk::Pixbuf)
              @fileList = Gtk::TreeView.new(@files)
              renderer = Gtk::CellRendererPixbuf.new
              col = Gtk::TreeViewColumn.new("Thumb", renderer, :pixbuf => 2)
              @fileList.append_column(col)
              renderer = Gtk::CellRendererText.new
              col = Gtk::TreeViewColumn.new("File name", renderer, :text => 1)
              @fileList.append_column(col)
              self.add @fileList
              sel = @fileList.selection
              sel.signal_connect("changed") do  sel 
                      if iter = sel.selected
                              puts "Double-clicked row contains name # iter[0] !"
                              self.signal_emit("selected", iter[0])
                      end
              end
      end
      def signal_do_selected(file)
            puts "Selected " + file
            #p caller
      end
      
      def readDir (root)
              Dir.foreach root do  dir 
                      file = root+'/'+dir
                      if !FileTest.directory?(file) && dir =~ /\.jpe?g$/ && FileTest.readable?(file)
                              thumb = getThumbnail(file)
                              iter = @files.append
                              iter[0] = file
                              iter[1] = dir
                              iter[2] = Gdk::Pixbuf.new thumb
                              File.delete(thumb)
                      end
              end
      end
end

And here's the controller code that binds the signal to some effect:

imageList.signal_connect("selected") do  imagelist, filename 
      puts "File # filename  was clicked!"
      image.load(filename)
end

It's quite easy, and (finally!) it does what I want without needing to write thousands of lines of code. YAY! And I finally fulfull my dream of connecting closures instead of callbacks to GTK signals. Yes, I could have done it in Perl. Yes I could have done it in Python. But Ruby is soo cute!