From KDE TechBase

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    The information below applies to older versions of Qt only. There are currently no Ruby bindings for Qt 5 and KDE Frameworks 5 available.

    Some important links are non-functional, specially the official Korundum page. Until we solve this problem you can find the source code at kdebindings project page

    Very complete bindings to both the KDE API and the Qt APIs. The Korundum package includes both a QtRuby Qt-only binding along with the full combined Qt/KDE one. The QtRuby package contains just Qt bindings with no dependencies on KDE.

    Korundum/QtRuby - Ruby-KDE/Qt bindings

    The book Rapid GUI Development with QtRuby (for Qt version 3.x) is available.

    Being Smoke-based bindings means that they offer full access to most KDE 4.x and Qt 4.x classes.


    Hello world example:

    #!/usr/bin/ruby -w
    require 'Qt4'
    a =
    hello ="Hello World!")
    hello.resize(100, 30)

    Hello Qt example in a more 'Rubyish' way:

    require 'Qt4' do do
            self.window_title = 'Hello QtRuby v1.0'
            resize(200, 100)
            button ='Quit') do
                connect(SIGNAL :clicked) { Qt::Application.instance.quit }
            label ='<big>Hello Qt in the Ruby way!</big>')
            self.layout = do
                add_widget(label, 0, Qt::AlignCenter)
                add_widget(button, 0, Qt::AlignRight)

    Current api coverage overview

    Available calls

    You can call all Qt public and protected methods, and all friend methods such as bitBlt() etc

    Virtual methods

    All virtual methods can be overridden, not just event handlers


    'foobar = 5' is a synonym for 'setFooBar(5)'

    Use either CamelCase or lowercase with underscore naming

    Any underscores in method names are removed, and the following character is capitalised. For example, you can use either of these two forms to call the same method:


    Operator overloading

    The full range of Qt operator methods is available, for example:

    p1 =,5)   => (5, 5)
    p2 =,20) => (20, 20)
    p1 + p2                   => (25, 25)

    Declare signals and slots

    Signals and slots are declared as list of strings like this:

    slots 'setColor(QColor)', 'slotLoad(const QString&)'..
    signals 'clicked()'..

    For slots and signals without arguments you can use Ruby symbols:

    slots :slotLoad
    signals :clicked

    Currently C++ type signatures must be used, a future version of QtRuby will allow ruby type signatures instead. (see the section on emitting Ruby Classes)

    Connect slots and signals like this:

    Qt::Object.connect( @colormenu, SIGNAL( "activated(int)" ),
                      self, SLOT( "slotColorMenu(int)" ) )

    There is also two another possibilities:

    connect(:mysig, mytarget, :mymethod))
    connect(SIGNAL('mysignal(int)'), mytarget, :mymethod))

    Or you can connect signal to a block:

    quit_button.connect(SIGNAL :clicked) { $qApp.quit }

    And emit signals like this:

    emit colorChanged( black )

    Emitting Ruby Classes

    Ruby classes can be emitted by embedding them inside a QVariant, and emitting the QVariant.

    The following code provides a method called to_variant that can be used to easily convert objects to Variants

    class Qt::RubyVariant < Qt::Variant
        def initialize(value)
            @value = value
        attr_accessor :value
    class Object
        def to_variant

    Note: as of KDE 4.5 you can simply use

    variant = Qt::Variant.fromValue(my_ruby_object)

    to create a QVariant that contains your ruby object. To get it back, you just call Qt::Variant#value as usual.

    This can be used as follows

    class MyObject < Qt::Object
        signals "mySignal(QVariant)"
        def doEmit
            # since KDE 4.5:
            # emit mySignal(Qt::Variant.fromValue(ruby_object))
            emit mySignal(ruby_object.to_variant)
        slots "mySlot(QVariant)"
        def mySlot(variant)
            ruby_object = variant.value

    Alternate way to emit Ruby Classes

    You can also try to emit a ruby class by emitting it's object_id (either as an Integer or a QVariant), and use ObjectSpace._id2ref to get the object back.

    class Object
        def to_variant
    class Qt::Variant
        def to_object
            ObjectSpace._id2ref to_int


    You can call constructors in the conventional style:

    quit ="Quit", self, "quit")

    Or you can pass a block if you prefer:

    w = { setCaption("foobar") }

    The block will be called in the context of the newly created instance.

    Ordinary arguments can be provided as well as a block at the end:

    w = { setCaption("foobar") }

    They are run in the context of the new instance.

    And there's more! You can also pass an arg to the block, and it will be run in the context of the arg:

    w = { |theWidget| theWidget.setCaption "foobar" }

    Garbage Collection

    When a ruby instance is garbage collected, the underlying C++ instance will only be deleted if it isn't 'owned' by a parent object. Normally this will 'just work', but there are occasions when you need to delete the C++ ahead of garbage collection, and whether or not it has a parent. Use the dispose(), isDisposed() and disposed? methods like this:

    if item2.disposed?
    puts "item2 is disposed"

    C++ 'int*' and 'int&' argument types

    Ruby passes numeric values by value, and so they can't be changed when passed to a method. The Qt::Integer class provides a mutable numeric type which does get updated when passed as an argument. For example, this C++ method 'findByFileContent()':

    # static Ptr findByFileContent( const QString &fileName, 
    #                               int *accuracy=0 );
    acc =
    fc = KDE::MimeType.findByFileContent("mimetype.rb", acc)

    It supports the arithmetic operators, and so expressions such as 'acc + 3' will work.

    C++ 'bool*' and 'bool&' argument types

    There is a similar problem for bool arg types, and the mutable Qt::Boolean class can be used like this:

    # QFont getFont(bool * ok, const QFont&initial, 
    #               QWidget* parent = 0, const char *name = 0);		
    ok =
    font = Qt::FontDialog.getFont(ok, 
              "Helvetica [Cronyx]", 10), 
    if !ok.nil? 
    # font is set to the font the user selected
    # the user canceled the dialog

    Use 'nil?' to test the value returned in the Boolean

    C++ (const )(unsigned )char* argument types

    In some cases Qt/KDE object "takes ownership" over Ruby String passed as char* argument type. Programmer needs to make sure that Ruby String is not being garbage collected or changed for the time it's being used by Qt/KDE object. It is also quite possible that Qt/KDE object will change and eventually free it(memory used internally by Ruby String to store its data). Be very careful when you call this kind of methods and make sure that there is no overloaded version witch accepts QString or QByteArray first!

    C++ unsigned char* functions

    Very few functions (as QImage::bits()) return a uchar* to directly manipulate data. These functions are not supported in Ruby and will throw an ArgumentError. More information on the mail list.


    If a method call can't be matched in the Smoke library giving a 'method_missing' error, first check that you are passing correct class instance that is properly initialized (with super method called in constructors of custom Qt classes descendants). You can also turn on debugging to trace the matching process:

    a =
    Qt.debug_level = Qt::DebugLevel::High
    a.loadLibrary("foo")  # Non existent method

    Will give the following output:

          classname    == QApplication
          :: method == loadLibrary$
          -> methodIds == []
          candidate list:
          Possible prototypes:
              static QWidget* QApplication::widgetAt(int, int, bool)

    Here, the list of candidate methods 'methodIds' is empty

    Another debugging mechanism allows various trace 'channels' to be switched on.

    You can trace virtual method callbacks:


    Or trace QtRuby garbage collection:


    String i18n

    QtRuby supports $KCODE values of 'u', 'e' and 's' or the corresponding '-K' options from the command line. Qt Designer .ui files have UTF-8 strings so if you use any 8 bit UTF-8 characters, you will need to set $KCODE='u' or use the -Ku command line option.

    Other capabilities and offerings

    Qt Designer

    A 'rbuic4' tool is included in qtruby/tools/rbuic to compile .ui files into ruby code. As described above, Qt Designer uses UTF-8. In addition to the options in the original uic C++ utility an '-x' flag has been added. This will generate a top level stub in the code:

    $ rbuic mainform.ui -x -o mainform.rb

    Will add this to the end of the generated code:

    if $0 == __FILE__
        a =
        w =

    Then you can test the example code straight away:

          $ ruby mainform.rb

    Use the '-kde' option to require the 'korundum4' extension rather than the 'Qt4' one. If the '-x' option is used in conjunction, it generates a KDE top level. For example:

    $ rbuic4 -x -kde knotifywidgetbase.ui -o knotifywidgetbase.rb

    Will generate this top level code:

    if $0 == __FILE__
        about ="knotifywidgetbase", 
     		                       "KNotifyWidgetBase", "0.1")
        KDE::CmdLineArgs.init(ARGV, about)
        a =
        w =

    Loading .ui files at runtime with Qt::UiLoader

    Let's say you created a file in your project directory called 'gui.ui' using Qt Designer ('/usr/bin/designer', comes with Qt. At least on Arch). You can load it like so:

    require 'Qt4'
    require 'qtuitools'
    class MyApp < Qt::Application
        def initialize
            super ARGV
            # 'gui.ui' was created with qt designer ('designer' on arch linux)
            file = 'gui.ui' do
                open Qt::File::ReadOnly
            window = file
            if window.nil?
                print "Error. Window is nil.\n"
    a =

    API reference

    Use the bin/rbqtapi tool to discover which methods are available in the QtRuby api. This command:

    $ rbqtapi Qt::TextEdit

    Will list all the methods in the Qt::TextEdit class

    $ rbqtapi -rsetCaption

    Lists all methods whose names contain the string 'setCaption'

    Example programs

    The best way to start programming QtRuby is to look at some existing code and start messing with it.. The are various samples under qtrubyexamples and korundum/examples.

    Writing Unit Tests

    Using Ruby allows you the power to leverage testing frameworks such as RSpec in order to unit and integration test your classes.

    Most classes such as Models can be easily tested via the APIs they expose. Below is a small extract with some interesting tests from the mingle_mover project ( The class being tested is a TableModel

    Note how we create a stub to pass to QAbstractTableModel::data, which accepts a QModelIndex as an argument.

    describe CardModel do
        it "Should Implement QAbstractTableModel" do
            CardModel.ancestors.should include Qt::AbstractTableModel
        it "Should Not Be Editable" do
  ,2), Qt::EditRole).should_not be_valid
            @model.headerData(nil, nil, Qt::EditRole).should_not be_valid
            flags = @model.flags(nil)
            flags.should have_flag Qt::ItemIsEnabled
            flags.should have_flag Qt::ItemIsSelectable
            flags.should_not have_flag Qt::ItemIsEditable
        it "Should not return any vertical headers" do
            @model.headerData(1, Qt::Vertical).should_not be_valid
        it "Should color a row according to the status" do
  ,2), Qt::ForegroundRole).value.color.should ==
  ,2), Qt::ForegroundRole).value.color.should ==
  ,0), Qt::ForegroundRole).should_not be_valid
        def mock_index(row, col)
            stub(:row => row, :column => col)
        def have_flag(flag)
            return simple_matcher("A flag that matches " + flag.to_s) { |given| (given & flag) != 0 }

    Testing Out Signals and Slots

    Below is a simple class which can be used to test out a class via the signals it emits:

    class RubySignalSpy < Qt::Object
        def self.create(*args, &block)
  *args, &block)
        def count(name)
        def params(name, invocation = 0)
        def method_missing(name, *args, &block)
            @calls[name.to_sym] << args
            exec_action_for(name, args)
        def responds_to?(name)
        def initialize
            @calls = {}
            def @calls.[](index)
                super || self[index] = []
            @actions = {}
        def mocked_slots(*names, &block)
            slots *names
            names.each { |name| @actions[name] = block }
        def exec_action_for(name, args)
            @actions[name].call(self, args) if @actions[name]
        def slots(*args)
          it "Should be able to emit a signal when called" do
            reciever = RubySignalSpy.create do
                slots "recieved(int, int)"                      # Explicitly name slots with parameters
                mocked_slot :some_other_slot do |spy, params|   # Pass a block to be executed when called
                end                                             # You must call mocked_slot with a symbol
            class ClassWeAreTesting < Qt::Object
                signals "sending(int, int)"
                def broadcast
                    emit sending(4, 2)
            sender =
            Qt::Object.connect(sender, SIGNAL("sending(int, int)"), reciever, SLOT("recieved(int, int)"))
            reciever.count(:recieved).should == 1               # Get count of calls
            reciever.params(:recieved, 0).should == [4, 2]      # Get the parameters of nth invocation

    Testing UI Classes

    It is much more difficult to test UI classes. In most cases, you will need to instantiate a QApplication so that you can create your widgets.

    Some rudimentary tests can be written by simulating clicks are various locations. Watch this space as more tests get written

    describe SomeTableView do
        before(:all) do
            @app =
            @view =
        it "Should accept a mouse click on second row"        
            @row2 = @view.rowViewportPosition 1
            @view.mousePressEvent(,,@row2), Qt::LeftButton, Qt::LeftButton, Qt::NoModifier))
            # Assert something here, such as that a signal has been emitted
        after(:all) do

    KDE Specific Infomation

    Instead of

    require 'Qt4'

    , use

    require 'korundum4'

    for KDE programs.

    The KDE K* classes such as KApplication are renamed as KDE::Application. The other KDE classes are in the KParts::, KIO:: or DOM:: namespaces, with the same names as their C++ counterparts.

    Use the 'rbkdeapi' script to introspect the Korundum api from the command line. For example:

    $ rbkdeapi KDE::Action

    Will list all the methods in the KDE::Action class. There are currently (as at KDE 3.3 beta 2) 977 classes/30841 methods in the Smoke library runtime, so the coverage of the Qt/KDE api is pretty complete.

    Build dependencies

    • ruby 1.8 or greater (svn trunk works with 1.9.1)
    • cmake 2.6 or greater
    • Qt 4.0 or greater
    • KDE 4.1 or greater (for korundum)


    There is a ruby translation of Qt Tutorial #1, and the corresponding ruby code is in qtruby/rubylib/tutorial/t1 to t14.

    And a Qt4 version of the same tutorial translated to Ruby by Darshan Ishaya Qt4 Ruby Tutorial

    Qt Tutorial #2, a Charting Application with ruby code in qtruby/rubylib/examples/qt-examples/chart.

    The Qt Designer Color Tool Tutorial, with ruby code in qtruby/rubylib/designer/examples/colortool.

    Paul Lutus has written a tutorial on how to get started with Ruby GUI programming with Qt

    For KDE, there is a ruby translation of this KDE 3.0 tutorial originally written for C++ by Antonio Larrosa Jiménez. The sources are in korundum/rubylib/tutorials/p1 to p9.

    The book Rapid GUI Development with QtRuby is now available.

    There is also an approach to create an Ruby-Qt/KDE Book under a free license. The content will be created in this wiki. The book made with latex will be derived from the content in the wiki. Any Questions? Contact me!


    You can obtain recent SVN snapshots on the Rubyforge QtRuby/Korundum site.

    More help

    There are two IRC channels (#qtruby and #kde-ruby) in FreeNode. If you prefer e-mail, you can use the kde-bindings mailing-list (low traffic) or ask in the ruby-talk mailing list (you may use the Ruby Forum gateway to post in ruby-talk from web).

    More information

    A series of articles on ruby QT (inspired by the work done for the dradis project):