Simple Ruby Plasmoid

on Kde, Ruby

Hello Planet KDE, hello RubyCorner

After some blog posts on my old blog about KDE programming with Ruby I decided to bring the content a little bit more to the people. Here I am.

Two days before yesterday I got a mail concerning a problem related to creating plasmoids with Ruby. I never had the wish to create my own plasmoid. I thought it would be difficult, but while getting a closer look, I’ve noticed how easy it is - in the case of using Ruby.

Simple Ruby Plasmoid

Simple Plasmoid made with Ruby This example is a modified version from the one in the KDE techbase wiki.

The plasmoid sends the content of a QLineEdit to the clipboard when pressing the QPushButton or pressing the enter key and clears the QLineEdit afterwards.

Test It

If you want to try it yourself, you just have to extract simple_ruby_plasmoid_clipboard.tar.gz, change the directory to ruby-test-applet and start the plasmoid in a special viewer with plasmoidviewer.

You have to install the Ruby KDE bindings package (on opensuse it is called ruby-kde4), but on a lot of KDE4 systems this should be installed already.

Understand It

First you need the right directory tree for your plasmoid. It should be look like this:

ruby-test-applet/
|-- contents
|   `-- code
|       `-- main.rb
`-- metadata.desktop

You need at least two files. The first one is main.rb, that contains your program code.

When accessing KDE libs from Ruby you write nearly the same code as you would write in C++.

A short example in C++:

setMinimumSize( 150, 150 )
Plasma::LineEdit line_edit( parent )

The same using Ruby:

set_minimum_size 150, 150
# or
setMinimumSize 150, 150
# or
self.minimum_size = 150, 150
line_edit Plasma::LineEdit.new self

Member variables begins with an @ sign. There are different aliases for KDE and Qt methods. You can omit brackets in a lot of cases. You don’t need any header files. You don’t need to compile.

require 'plasma_applet'

module RubyTestApplet
  class Main < PlasmaScripting::Applet

    slots :addText

    def init
      set_minimum_size 150, 150

      @layout = Qt::GraphicsLinearLayout.new Qt::Vertical, self
      self.layout = @layout

      @label = Plasma::Label.new self
      @label.text = 'This plasmoid will copy the text you enter below to the clipboard.'
      @layout.add_item @label

      @line_edit = Plasma::LineEdit.new self

      begin
        @line_edit.clear_button_shown = true # not supported in early plasma versions
      rescue
        nil # but that doesn't matter
      end

      @layout.add_item @line_edit

      @button = Plasma::PushButton.new self
      @button.text = 'Copy to clipboard'
      @layout.add_item @button

      Qt::Object.connect( @button, SIGNAL(:clicked), self, SLOT(:addText) )
      Qt::Object.connect( @line_edit, SIGNAL(:returnPressed), self, SLOT(:addText) )
    end

    def addText
      Qt::Application.clipboard.text = @line_edit.text
      @line_edit.text = ""
    end

  end
end

# kate: remove_trailing_space on; replace-trailing-space-save on; indent-width 2; indent-mode ruby;

The second file you need is the metadata.desktop containing all the meta data. :wink:

[Desktop Entry]
Name=Simple Ruby applet
Comment=This is a simple applet written in Ruby
Icon=chronometer
Type=Service
ServiceTypes=Plasma/Applet

X-Plasma-API=ruby-script
X-Plasma-MainScript=code/main.rb

X-KDE-PluginInfo-Author=Me
X-KDE-PluginInfo-Email=me@example.com
X-KDE-PluginInfo-Name=ruby-test
X-KDE-PluginInfo-Version=0.1
X-KDE-PluginInfo-Website=http://plasma.kde.org/
X-KDE-PluginInfo-Category=Examples
X-KDE-PluginInfo-Depends=
X-KDE-PluginInfo-License=GPL
X-KDE-PluginInfo-EnabledByDefault=true

metadata.desktop

What do you think? So easy, isn’t it? If you have ever played a little bit with Ruby and Qt or KDE you should know enough to create your own plasmoid within a quarter of an hour!