Building native Android applications with Mirah and Pindah

So you want to build Android apps… without Java?
Nick Plante @zapnap
(A brief introduction to Mirah and Pindah)

Who?
Nick Plante
(not a Java developer)
Zerosum Labs
Rails Rumble
Rubydoc.info
Chinaccelerator
Contact me!
@zapnap on Twitter
http://github.com/zapnap

Why?
Because you’re a Ruby developer (familiarity).
Because Android is awesome.
Because simplicity is elegance.
“Think Different.”

Java vs Ruby
Dynamic vs Static
Simplicity vs Complexity & Verbosity
Less Ceremony
Java is a systems programming language, after all
But… The JVM is an awesome platform
Android’s use of the JVM (Dalvik) gives us options

Java Alternatives
Android Scripting Environment (SL4A)
Great for scripting; not great for applications
Limited access to Android API / GUI
Performance issues
Other JVM-based languages:
Scala
Clojure
JRuby
Mirah
Groovy?

JRuby & MrRuboto
Ruboto is your friend!
JRuby interface / framework for Android APIs
http://ruboto.org
But JRuby runtime overhead is a problem
Slow startup (~10 seconds)
Large APK size
HelloWorld: 3.4MB compressed, 10MB installed

Introducing Mirah
Mirah compiles straight to Java bytecode
Very fast, no extra overhead
Syntax is very Ruby-ish
Statically-typed with local type inference
“Ruby with type annotations”
No runtime library
Mix and match Java code

Warning!
Mirah is still a very young language (v0.0.7)
Tooling is very, very alpha
Advantage: Eclipse (Java)
Redcar looks promising
Compilation errors are very, very not-so-fun
NativeException: jmeta.SyntaxError: expected Ensure before ' { |a b| Inte' (at line: 16, char: 40)

One thing at a time
We’ll get to Android in just a second
First let’s see some basic Mirah syntax…

# fib.mirah
def fib(a:int):int
if a < 2
a
else
fib(a-1) + fib(a-2)
end
end
puts fib(20)
Ruby vsMirah
Parameter type declaration???
SRSLY? 
# fib.ruby
def fib(a)
if a < 2
a
else
fib(a-1) + fib(a-2)
end
end
puts fib(20)
Return type can often be inferred.

.class output
Produces a java .class
$ mirahcfib.mirah
public static intfib(int)
Can also produce .java code
$ mirahc -jfib.mirah
* I have no idea why you would want to do this.

.to_java => “ick”
// Generated from hello.mirah
public class Hello extends java.lang.Object {
public static void main(java.lang.String[] argv) {
java.io.PrintStream temp$1 = java.lang.System.out;
temp$1.println(Hello.fib(20));
}
public static intfib(int a) {
return (a < 2) ? (a) : ((Hello.fib((a - 1)) + Hello.fib((a - 2))));
}
}

Challenges / Major Differences
Java stdlib: both a blessing and a curse
List, HashMap, etc
arr.get(1) vs arr[0]
Blocks work, but syntactic sugar required
For example, List#eachcan be used (array)
But HashMap#eachdoes not exist
No optional arguments, no *splats, no ranges

Using Java’s Standard Library
import java.util.Collections
import java.util.HashMap
import java.util.List
class ListPrinter
def print(list:List)
puts "first item: #{list.get(0)}"
list.each do |item|
puts "item: #{item}"
end
end
end
class HashPrinter
def print(map:HashMap)
map.keySet.each do |key|
puts "#{key}: #{map.get(key)}"
end
end
end
map = { 'batman' => 'brucewayne', 'superman' => 'clarkkent' }
HashPrinter.new.print(map)
list = ['peter', 'stewie', 'brian']
ListPrinter.new.print(list)

Get Mirah
# Install JRuby 1.6 if you haven’t already
# (or rvm use jruby)
$ jruby –S gem install mirah
$ mirah-e "puts 'hello world'”
> hello world

Now What?

Get the Android SDK
Download and install it:
http://developer.android.com/sdk/index.html
Notes on building from the command line:
http://developer.android.com/guide/developing/projects/projects-cmdline.html
Set up your environment (see above):
Make sure to set JAVA_HOME, CLASSPATH, and put your platform-tools directory in your path

Android SDK / Virtual Devices

The anatomy of a typical Android application
Activities
Intents
Manifest File
XML Layouts (Views)
Services
Content Providers
(Lots to learn)

Hello Pindah
Garrett, Protoform, Mirahndroid => Pindah
Goals
Make it easy to get started with Android + Mirah
Make day to day development tasks easier
Provide project structure and conventions
Application skeleton generator
Rake tasks to hide Ant nastiness
Because XML is pain
Use Rake to compile / debug / install / etc

What Pindah Does NOT Do
No “pretty” wrappers for Android APIs
You must learn the APIs to work effectively
Does not provide alternatives to XML-based Manifest or view layouts
https://github.com/objo/droid-views

Get Pindah
# For more information, see
# http://github.com/mirah/pindah
$ jruby –S gem installpindah
# Generate an Android application skeleton
$pindahcreate org.example.hello [/path/to/hello_world] [HelloActivity]

Android App Skeleton
├── AndroidManifest.xml
├── Rakefile
├── libs
├── res
│ ├── drawable-hdpi
│ │ └── ic_launcher.png
│ ├── drawable-ldpi
│ ├── drawable-mdpi
│ ├── layout
│ │ └── main.xml
│ └── values
│ └── strings.xml
└── src
└── org
└── example
└── hello
└── HelloActivity.mirah
Managed for you by Pindah:
default.properties
build.properties
local.properties
build.xml

Pindah Rake Tasks
$ rake -T
Android SDK Tools Revision 8
Project Target: Android 2.1-update1
API level: 7
------------------
Resolving library dependencies:
No library dependencies.
------------------
Importing rules file: tools/ant/main_rules.xml
rake clean # Removes output files created by other targets.
rake compile # Compiles project's .mirah files into .class files
rake debug # Builds the application and signs it with a debug key.
rake install # Installs/reinstalls the debug package onto a running ...
rake javac # Compiles R.java and other gen/ files.
rake logcat # Tail logs from a device or a device or emulator
rake release # Builds the application.
rake spec # Print the project spec
rake uninstall # Uninstalls the application from a running emulator or dev...

Android Activity Boilerplate
# HelloActivity.mirah
package org.example.hello
import android.app.Activity
class HelloActivity < Activity
def onCreate(state)
super state
setContentViewR.layout.main
end
end
# HelloActivity.java
package org.example.hello;
import android.app.Activity;
public class HelloActivity
extends Activity
{
/** Called when the activity is first created. */
@Override
public void onCreate(
Bundle savedInstanceState)
{
super.onCreate(
savedInstanceState);
setContentView(
R.layout.main);
}
}

Running the Example App
$ cdhello_world
$ rake install
=> WIN.

Well, that was boring

Slightly More Interesting
More expressive code == visible improvement
Example application
“Up or Down?” website testing app
http://github.com/zapnap/upordown
Questions:
What do Android callbacks look like?
How do I leverage 3rd party (Java) libraries?
How do I handle exceptions?
How does Mirah deal with scope? (it’s weird)

Up or Down? Down or Up?

Android Listeners (Java)
// Sample button click listener in Java
// Create an anonymous implementation of OnClickListener
private OnClickListenermClickListener = new OnClickListener() {
public void onClick(Viewv) {
// handle click event
}
};
protected void onCreate(BundlesavedValues) {
...
// Capture our button from layout
Button mSubmit = (Button)findViewById(R.id.submit_btn);
// Register the onClick listener with theimpl above
mSubmit.setOnClickListener(mClickListener);
...
}

StatusActivity + Listeners
class StatusActivity < Activity
def onCreate(state)
super state
setContentViewR.layout.main
@url = EditTextfindViewById(R.id.url_txt)
@submit = Button findViewById(R.id.submit_btn)
setListeners
end
def setListeners
this = self
# SHORTCUT: click listener must implement onClick
@submit.setOnClickListener do |v|
status = this.checkSiteStatus(this.getUrl)
this.showResult status
end
end
Scoping for ivars and self is incomplete. Assign a local var within scope.
Easy to add anonymous listeners with this syntax (implements a single method interface)

Using External Java Libraries
Put jars in libs folder and import to use. Simple! (must import Android libs too)
import java.net.URL
import java.net.SocketTimeoutException
import org.jsoup.Jsoup
import org.jsoup.nodes.Document
def checkSiteStatus(address:String):String
return "Please specify a URL to test" if address.equals('')
begin
doc = Jsoup.connect(
"http://downforeveryoneorjustme.com/" + address
).get
res = doc.select("#container").first.text
Log.d 'StatusActivity',
'Full response from server is: ' + res
res.substring(0, res.indexOf('Check another'))
rescue SocketTimeoutException => ex
"Unable to contact the server. How ironic!”
end
end
Exception handling works like it does in Ruby. Must import specific exceptions.

Wrapping Up: Dialog Example
def getUrl
@url.getText.toString
end
def showResult(message:String)
alert = AlertDialog.Builder.new(self)
alert.setTitle 'Site Test Results’
alert.setMessage message
alert.setPositiveButton('OK') do |dialog, w|
dialog.dismiss
end
alert.show
end

Android XML Layouts (main.xml)
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout
android:orientation="vertical"
android:layout_height="wrap_content">
<TextView
android:layout_height="wrap_content"
android:gravity="center_horizontal"
android:textSize="20sp"
android:textStyle="bold"
android:text="@string/app_title" />
<TextView
android:textSize="18sp"
android:textStyle="bold"
android:layout_marginBottom="10dip"
android:text="@string/app_subtitle" />
<EditTextandroid:id="@+id/url_txt"
android:singleLine = "true"
android:inputType="textUri"
android:hint="@string/url_example" />
<Button android:id="@+id/submit_btn"
android:layout_width="140dip"
android:layout_marginTop="6dip"
android:layout_gravity="center"
android:gravity="center"
android:text="@string/submit_btn" />
</LinearLayout>
<TextView
android:layout_alignParentBottom="true"
android:autoLink="web"
android:text="@string/powered_by" />
</RelativeLayout>
<EditTextandroid:id="@+id/url_txt"
android:singleLine = "true"
android:inputType="textUri"
android:hint="@string/url_example" />
more info
app title
[ url input ]
[ button]

One More Thing
Android Manifest lists top-level activities and required permissions
Our app requires Internet access
Add the permission to AndroidManifest.xml:
<uses-permission android:name="android.permission.INTERNET" />

It Works!

Ideas for Next Steps
Implement a ProgressDialog
And perform the site check in an AsyncTask
Record a log of website test history to a ListView
Allow users to browse test history through a separate Activity
Store test history to a local Sqlite database (and ListAdapter)
Fork me at
http://github.com/zapnap/upordown

Conclusions (or lack thereof)
Mirah is a nice midpoint between Ruby and Java
Well-suited for Dalvik JVM work
But still very immature / not yet practical for daily use
Opportunity to help push mobile dev forward
Lack of good IDE support
Makes working with the (massive) Android API difficult
Debugging is a pain in the butt
ADB (Rake logcat) is incredibly useful; learn to use it
I personally still prefer mobile web development ;-) but sometimes native is the way to go!

And so it goes
Mirah Language Resources
http://mirah.org
http://github.com/mirah/mirah
Pindah and Mirah and Android Oh My!
http://github.com/mirah/pindah
http://github.com/technomancy/garrett (experiments)
http://threebrothers.org/brendan (urbanspoon)
General Android Development
http://developer.android.com/sdk/index.html
http://developer.android.com/guide/developing/projects/projects-cmdline.html

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Building native Android applications with Mirah and Pindah

by Nick Plante

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