ruby-qml Gem Version

ruby-qml is a QML / Qt Quick wrapper for Ruby. It provides bindings between QML and Ruby and enables you to use Qt Quick-based GUI from Ruby.

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What you can do with ruby-qml

  • Develop desktop GUI applications only with Ruby and QML / JavaScript
  • Easily combine codes written in C++ and Qt with your Ruby code





  • Ruby 2.1 or later
  • OS X or Linux
  • Qt 5.4 or later

OS X with Homebrew

To install ruby-qml on OS X with Homebrew, run the following commands:

$ brew install qt5
$ gem install qml -- --with-qmake=$(brew --prefix qt5)/bin/qmake

Both libffi and Qt5 are keg-only in Homebrew, so you must specify their paths explicitly (or force linking).

If you use official Qt installation, for example:

$ gem install qml -- --with-qmake=$HOME/Qt/5.4/clang_64/bin/qmake

The Qt installation path ($HOME/Qt/5.4/clang_64 in this example) depends on your Qt installation configuration and Qt version.

General (OSX and Linux)

$ gem install qml


$ sudo apt install ruby ruby-dev build-essentials qt5-default qtdeclarative5-dev qtbase5-private-dev qml-module-qtquick2 qml-module-qtquick-controls
$ sudo gem install qml


Using Ubuntu as the linux distro, proceed as above and use either WSL2 or an XServer (e.g. vcxsrv) to show the UI on Windows.


  • --with-qmake=[dir]
    • Qt qmake executable path (optional).

Use Gemfile

Add this line to your Gemfile:

gem 'qml'

And then execute:

$ bundle install

To pass build options, use bundle config. For example:

$ bundle config build.qml --with-qmake=$(brew --prefix qt5)/bin/qmake

The configuration will be saved in ~/.bundle/config.


Load QML file

The following code loads a QML file and shows an application window titled "Hello, world!".

require 'qml' do |app|
  app.load_path Pathname(__FILE__) + '../main.qml'
// main.qml
import QtQuick 2.2
import QtQuick.Controls 1.1

ApplicationWindow {
    visible: true
    width: 200
    height: 100
    title: "Hello, world!"

Use Ruby class in QML

To make your class available to QML, include QML::Access and call register_to_qml.

By including QML::Access, you can also define properties and signals in Ruby classes like in QML.

Properties are used to bind data between QML and Ruby. Signals are used to provide the observer pattern-like notification from Ruby to QML.


# Ruby
class FizzBuzz
  include QML::Access
  register_to_qml under: "Example", version: "1.0"

  property(:input) { '0' }
  property(:result) { '' }
  signal :inputWasFizzBuzz, []

  on_changed :input do
    i = input.to_i
    self.result = case
    when i % 15 == 0
    when i % 3 == 0
    when i % 5 == 0

  def quit
    puts "quitting..."
// QML - main.qml
import QtQuick 2.2
import QtQuick.Controls 1.1
import QtQuick.Layouts 1.1
import Example 1.0

ApplicationWindow {
    visible: true
    width: 200
    height: 200
    title: "FizzBuzz"

    ColumnLayout {
        anchors.fill: parent
        anchors.margins: 10
        TextField {
            placeholderText: "Input"
            text: "0"
            id: textField
        Text {
            id: text
            text: fizzBuzz.result
        Button {
            text: 'Quit'
            onClicked: fizzBuzz.quit()
        Text {
            id: lastFizzBuzz
    FizzBuzz {
        id: fizzBuzz
        input: textField.text
        onInputWasFizzBuzz: lastFizzBuzz.text = "Last FizzBuzz: " + textField.text

You can omit arguments of register_to_qml if they are obvious:

module Example
  VERSION = '1.0.0'

  class FizzBuzz
    include QML::Access


Pass data to QML ListModels

To bind list data between QML ListView and Ruby, you can use ListModels.

  • QML::ListModel - the base class for ruby-qml list models.

  • QML::ArrayModel - provides a simple list model implementation using Array.

  • QML::QueryModel - for databases (like ActiveRecord, Sequel or something)

This example uses ArrayModel to provide list data for a QML ListView. When the content of the ArrayModel is changed, the list view is also automatically updated.


# Ruby
class TodoController
  include QML::Access
  register_to_qml under: "Example", version: "1.0"

  property(:model) {, :description, :due_date) }

  def add(title, description, due_date)
    # Items of list models must be "Hash-like" (have #[] method to get columns)
    item = {
      title: title,
      description: description,
      due_date: due_date
    model << item
// QML
ListView {
    model: todo.model
    delegate: Text {
        text: "Title: " + title + ",  Description: " + description + ", Due date: " + due_date
TodoController {
  id: todo

Combile asynchronous operations

In QML, all UI-related operations are done synchronously in the event loop. To set result of asynchronous operations to the UI, use QML.next_tick.


# Ruby
class HeavyTaskController
  include QML::Access
  register_to_qml under: "Example", version: "1.0"

  property(:result) { '' }

  def set_result(result)
    self.result = result

  def start_heavy_task do
      QML.next_tick do
        set_result do_heavy_task()
// QML
Text {
  text: controller.result
Button {
  text: "Start!!"
  onClicked: controller.start_heavy_task()
HeavyTaskController {
  id: controller

Value conversions between Ruby and QML JavaScript

Ruby to QML

Ruby QML/JavaScript
nil null
true/false boolean
Numeric number
String/Symbol string
Array Array
Hash plain Object
Proc Function
Time Date
QML::Access Object(QObject derived)
QML::ListModel Object(QAbstractListModel)

You can customize this by implementing #to_qml method.

QML to Ruby

QML/JavaScript Ruby
null/undefined nil
boolean true/false
number Float
string String
Array QML::JSArray
Function QML::JSFunction
Object QML::JSObject
Object wrapping QML::Access QML::JSWrapper

You can convert Objects further through QML::JSObject methods.

QML::JSObject usage

QML::JSObject is the wrapper class for JavaScript objects.

obj = QML.engine.evaluate <<-JS
    value: 1,
    add: function(d) {
      this.value += d;

# Getter
obj.value #=> 1

# Setter
obj.value = 2
obj.vaue #=> 2

# Call method if the property is a function
obj.value #=> 11

# Subscription
obj[:value] #=> 11
obj[:add] #=> #<QML::JSFunction:...>

Load and use Qt C++ plugins

PluginLoader loads Qt C++ plugins. It enables you to use your Qt C++ codes from Ruby easily.

// C++ - plugin example
class MyPlugin : public QObject
    Q_PLUGIN_METADATA(IID "org.myplugin.MyPlugin")
    void added(int value);

public slots:
    int add(int x, int y) {
        int result = x + y;
        emit added(result);
        return result;
# Ruby

# The instance will be a `QML::JSObject` which represents the plugin Qt object
plugin =, "myplugin").instance

# Connect to signal (see
plugin[:added].connect do |value|
  puts "added value: #{value}"

plugin.add(1, 2) #=> 3

Use with EventMachine

You can use EventMachine with ruby-qml. It is more powerful than the default ruby-qml event loop.

Instead of using, start an EventMachine event loop by and process QML events periodically by QML::Application#process_events.

require 'qml'
require 'eventmachine' do
  EM.add_periodic_timer(0.01) { QML.application.process_events }
  QML.application.load_path(Pathname.pwd + 'main.qml')

You can also use em-synchrony to write callback-free asynchronous operation for ruby-qml.

require 'qml'
require 'eventmachine'
require 'em-synchrony'
require 'em-http-request'

class Controller
  include QML::Access
  property(:result) { '' }

  def get
    EM.synchrony do
      content = EM::Synchrony.sync'').get
      self.result = content.response

  def quit

  register_to_qml under: 'Example', version: '0.1'
end do
  EM.add_periodic_timer(0.01) { QML.application.process_events }
  QML.application.load_path(Pathname.pwd + 'main.qml')


Init submodules

$ git submodule init
$ git submodule update

Install dependencies

$ bundle install

Build native extension

Before running ruby-qml in development, the native extension of ruby-qml needs to have been built. To build it, run the following commands:

$ cd ext/qml
$ bundle exec ruby extconf.rb --with-qmake=/path/to/qmake
$ make -j4

Run tests

Tests for ruby-qml is written in RSpec. To run tests, do:

$ bundle exec rspec

Run examples

$ bundle exec ruby examples/fizzbuzz/fizzbuzz.rb

Send pull requests

  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Write some tests
  5. Push to the branch (git push origin my-new-feature)
  6. Create new Pull Request