The core components of Ruby on Android
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Ruboto Core

Ruby on Android.


$ gem install ruboto-core

Getting Started

Before you use Ruboto, you should do the following things:

  • Install the JDK if it's not on your system already
  • Install jruby if you don't already have it. JRuby has a very easy install process, or you can use rvm
  • Install the Android SDK
  • Add the sdk's tools/ directory to your $PATH
  • Generate an Emulator image unless you want to develop using your phone.

General Information

The Rakefile assumes that you are in the root directory of your app, as do all commands of the ruboto command line utility, other than ruboto gen app.

The Rakefile requires you to run it through JRuby's rake.

Command-line Tools

Application generator

$ ruboto gen app --package com.yourdomain.whatever --path path/to/where/you/want/the/app --name NameOfApp --target android-version --min-sdk another-android-version --activity MainActivityName

Version values must be specified using'android-' and the sdk level number (e.g., android-8 is froyo).

Class generator

Generates a Java class (Activity, Service, or BroadcastReceiver) associated with a specific ruboto script. The generator also generates a corrsponding test script.

$ ruboto gen class ClassName --name YourObjectName

Ex: $ ruboto gen class BroadcastReceiver --name AwesomenessReceiver

Callback generator

Can subclass any part of the Android API to pass control over to a script when the specified methods are called. You can also create classes that implement a single Android interface to pass control over to ruboto.

For classes that need subclassing (e.g., PhoneStateListener, SQLiteOpenHelper, View)

$ ruboto gen subclass AndroidPackageAndClassName --name YourClassName --method_base all-on-or-none --method_include methods --method_exclude methods

Ex: $ ruboto gen subclass android.telephony.PhoneStateListener --name MyPhoneStateListener --method_base on

For interfaces that need implementing (e.g., OnClickListener or SensorListener)

$ ruboto gen interface AndroidPackageAndInterfaceName --name YourClassName

Ex: $ ruboto gen interface android.hardware.SensorListener --name MySensorListener

Inside your script use:

# note that this is different than java_import
ruboto_import "your.package.MySensorListener"


# Create the callback object
@sensor_listener =

# Specify the block to call 
@sensor_listener.handle_sensor_changed do |sensor, values|
  # Do stuff

# Register the listener

Packaging task

This will generate an apk file.

$ rake

To generate an apk and install it to a connected device (or emulator) all in one go, run

$ rake install

Deployment task

When you're ready to post your app to the Market, you need to do a few things.

First, you'll need to generate a key to sign the app with using keytool if you do not already have one. If you're ok with accepting some sane defaults, you can use $ ruboto gen key --alias alias_for_your_key with an optional flag --keystore /path/to/keystore.keystore, which defaults to ~/.android/production.keystore. It will ask for a password for the keystore and one for the key itself. Make sure that you remember those two passwords, as well as the alias for the key.

Also make sure to keep your key backed up (if you lose it, you won't be able to release updates to your app that can install right over the old versions), but secure.

Once you have your key, use the rake publish task to generate a market-ready .apk file. You will need the RUBOTO_KEYSTORE and RUBOTO_KEY_ALIAS environment variables set to the path to the keystore and the alias for the key, respectively. So either run $ RUBOTO_KEYSTORE=~/.android/production.keystore RUBOTO_KEY_ALIAS=foo rake publish or set those environment variables in your ~/.bashrc or similar file and just run $ rake publish Now get that .apk to the market!

Updating Your Scripts on a Device

With traditional Android development, you have to recompile your app and reinstall it on your test device/emulator every time you make a change. That's slow and annoying.

Luckily, with Ruboto, most of your changes are in the scripts, not in the compiles Java files. So if your changes are Ruby-only, you can just run

$ rake update_scripts

to have it copy the current version of your scripts to your device.

Sorry if this takes away your excuse to have sword fights:

XKCD Code's Compiling


This only works if your changes are all Ruby. If you have Java changes (which would generally just mean generating new classes) or changes to the xml, you will need to recompile your script.

Also, you need root access to your device for this to work, as it needs to write to directories that are read-only otherwise. The easiest solution is to test on an emulator, but you can also root your phone.

Updating Ruboto's Files

You can update various portions of your generated Ruboto app through the ruboto command:

  • JRuby:
  1. If a new version of JRuby is released, you should update your gem (e.g., sudo gem update jruby-jars).

  2. From the root directory of your app:

    $ ruboto update jruby

  • The ruboto.rb script:
  1. From the root directory of your app:

    $ ruboto update ruboto

  • The core classes (e.g., RubotoActivity):
  1. These classes are generated on your machine based on the SDKs (min and target) specified when you 'gen app' (stored in the AndroidManifest.xml)

  2. You many want to regenerate them if a new version of the SDK is released, if you change your targets, or if you want more control over the callbacks you receive.

  3. From the root directory of your app:

    $ ruboto gen core Activity --method_base all-on-or-none --method_include specific-methods-to-include --method_include specific-methods-to-exclude

  4. The generator will load up the SDK information and find the specified methods. The generator will abort around methods that were added or deprecated based on the SDK levels. You can either use method_exclude to remove methods individually or add '--force exclude' to remove the all. You can also us '--force include' to create them anyway (added methods are created without calling super to avoid crashin on legacy hardware).


The main thing Ruboto offers you is the ability to write Ruby scripts to define the behavior of Activites, BroadcastReceievers, and Services. (Eventually it'll be every class. It's setup such that adding in more classes should be trivial.)

Here's how it works:

First of all, your scripts are found in src/ and the script name is the same as the name of your class, only under_scored instead of CamelCased. Android classes have all of these methods that get called in certain situations. Activity.onDestroy() gets called when the activity gets killed, for example. Save weird cases (like the "launching" methods that need to setup JRuby), to script the method onFooBar, you call the Ruby method handle_foo_bar on the Android object. In your scripts, they are defined as $class_name. That was really abstract, so here's an example.

You generate an app with the option --activity FooActivity, which means that ruboto will generate a FooActivity for you. So you open src/foo_activity.rb in your favorite text editor. If you want an activity that does nothing but Log when it gets launched and when it gets destroyed (in the onCreate and onPause methods). You want your script to look like this:

require 'ruboto.rb' #scripts will not work without doing this
$activity.handle_create do |bundle|
  Log.v 'MYAPPNAME', 'onCreate got called!'
  handle_pause do
    Log.v 'MYAPPNAME', 'onPause got called!'

If you prefer, you can also do this. It's equivalent:

require 'ruboto.rb' #scripts will not work without doing this
$activity.handle_create do |bundle|
  Log.v 'MYAPPNAME', 'onCreate got called!'
$activity.handle_pause do
  Log.v 'MYAPPNAME', 'onPause got called!'

Each class has only one method that you can nest other calls inside of (ie. what is happening in that first example that removes the need for the second $activity.). For Activities and Services, it is handle_create, and for BroadcastReceivers, it is handle_receive. The general rule is that it corresponds to the first method in the class's lifecycle. But you should never really have to think about it because generating a class generates a sample script that calls that method.

The arguments passed to the block you give handle_ methods are the same as the arguments that the java methods take. Consult the Android documentation.

Activities also have some special methods defined to make things easier. The easiest way to get an idea of what they are is looking over the demo scripts. You can also read the ruboto.rb file where everything is defined.


For each generated class, a ruby test script is created in the test/assets/scripts directory. For example if you generate a RubotoSampleAppActivity a file test/assets/scripts/ruboto_sample_app_activity_test.rb file is created containing a sample test script:

activity Java::org.ruboto.sample_app.RubotoSampleAppActivity

setup do |activity|
  start =
  loop do
    @text_view = activity.findViewById(42)
    break if @text_view || ( - start > 60)
    sleep 1
  assert @text_view

test('initial setup') do |activity|
  assert_equal "What hath Matz wrought?", @text_view.text

test('button changes text') do |activity|
  button = activity.findViewById(43)
  assert_equal "What hath Matz wrought!", @text_view.text

You run the tests for your app using ant or rake

$ jruby -S rake test

$ cd test ; ant run-tests


Want to contribute? Great! Meet us in #ruboto on, fork the project and start coding!

"But I don't understand it well enough to contribute by forking the project!" That's fine. Equally helpful:

  • Use Ruboto and tell us how it could be better.
  • As you gain wisdom, contribute it to the wiki
  • When you gain enough wisdom, reconsider whether you could fork the project.

If contributing code to the project, please run the exising tests and add tests for your changes. You run the tests using rake

$ jruby -S rake test

Getting Help

  • You'll need to be pretty familiar with the Android API. The Developer Guide and Reference are very useful.
  • There is further documentation at the wiki
  • If you have bugs or feature requests, open an issue on GitHub
  • You can ask questions in #ruboto on and on the mailing list
  • There are some sample scripts (just Activities) here

Tips & Tricks


If you're doing a lot of Android development, you'll probably find yourself typing emulator -avd name_of_emulator a lot to open emulators. It can be convenient to alias these to shorter commands.

For example, in your ~/.bashrc, ~/.zshrc, or similar file, you might put alias eclair="emulator -avd eclair" alias froyo="emulator -avd froyo" If you have an "eclair" emulator that runs Android 2.1 and a "froyo" one that runs Android 2.2.


If Ruboto's performance is a problem for you, or you want something that gives you total access to the android API (as Ruboto does not yet do), check out Mirah and Garrett.

Mirah, formerly known as Duby, is a language with Ruby-like syntax that compiles to java files. This means that it adds no big runtime dependencies and has essentially the same performance as writing Java code because it essentially generates the same Java code that you would write. This makes it extremely well-suited for mobile devices where performance is a much bigger consideration.

Garrett is a "playground for Mirah exploration on Android."

Domo Arigato

Thanks go to:

  • Charles Nutter, a member of the JRuby core team, for mentoring this RSoC project and starting the Ruboto project in the first place with an irb
  • All of Ruby Summer of Code's sponsors
  • Engine Yard in particular for sponsoring RSoC and heavily sponsoring JRuby, which is obviously critical to the project.
  • All contributors and contributors to the ruboto-irb project, as much of this code was taken from ruboto-irb.