Setting up for better Scala development on Android

2013-09-04

I did a tutorial how to set up everything using IntelliJ a while ago. I still think IntelliJ IDEA is awesome and you should use it(it has a free and open version) but I’ve found a better way. No more clicking around in wizards…it’s config file time. Relax - it’s quite simple. I recommend installing the Typesafe-stack. It gives you the two tools listed below in nice packaged form with updates. And that’s about it. I’m quite fond of package managers => one place to update everything.

SBT

Simple Build Tool. Exactly what the name says. Simple. But boy it’s powerful. And it has a pluginfor doing android development. Batteries included(managing emulator & packaging all from one place). And it prefers convention over configuration. Great. All this leads to quick results.

Giter8

Maven has archetypes and that’s a great feature since it enables you to just start developing your application without messing with build settings to get the damn thing to compile. SBT doesn’t have that. But there’s a third-party tool that does something possibly even better. Yes, giter8 or g8 for short(that’s the command line too). A tool that fetches templates from github(or any other git repo in recent versions) asks you for few parameters and creates a project for you. Super simple to use and not that hard to create your own templates.

Let’s get cracking

Use g8 to create an app and configure it

g8 jberkel/android-app

Template for Android apps in Scala

package [my.android.project]: com.edofic.demoapp
name [My Android Project]: DemoApp
main_activity [MainActivity]:
scala_version [2.9.2]: 2.9.1
api_level [10]:
useProguard [true]: false
scalatest_version [1.8]:

Applied jberkel/android-app.g8 in demoapp

This is from interactive session. Stuff after colons is my input…eh I won’t try to explain. Just try it. Explanation on parameters is in place though. Template is from the author of the plugin; I used default activity name because I don’t care. Scala version is 2.9.1 because that’s what’s preinstalled on my phone(more on that later) and ProGuard is off to exclude scala standard library from the dexing step. See SBT is know that scala standard library doesn’t fit through dexing and excludes it. But it does some magic too. Whole packaging process is 2-3x than ant/maven/eclipse/idea. And again twice faster if you use 2.10(RC5) instead of 2.9.x. It gets under 10s on a good machine. Sadly my laptop is not that fast so I use predexed scala library to get under that magical 10s. Essentially I’m telling the compiler not to bother with the library and take care of it myself. There are two ways of doing that. Note that you only need to do this once per device.

Patching the device/emulator

Modify boot classpath and add libraries. Some nasty bootimage manipulation for real devices. Simple script for emulator. What I use for most development. Seehere how to do it.

Shared libraries

This is how Google provides libraries for their maps API on android. There’s even anapp on Play store that does that for you(requires root). More info on their github page. The downside is you need to include a few lines into your manifest(just development, you take it out for the release). I need to do more research on this - maybe gonna post a guide when I figure out how to install custom versions of scala like that.

Compiling and running

Here comes a quirk. Plugin doesn’t play nice with latest version of sbt. Fortunately sbt is capable of running different versions without any hassle. You can provide “-sbt-version 0.12.0” every time or create a project/build.properties with “sbt.version=0.12.0” in it(or use my template - g8 edofic/android-app). This starts up sbt and does compile-deploy-start operation.

sbt
....
android:start-debug

Checkout the plugin page for list of available commands.

Why SBT?

I’ve only been converted recently but I’ve already found a bunch of nice stuff I can do now. Firstly..dependency management. Now it’s a breeze. Typed resources via source generation - no more casting and exceptions on findViewByID(see plugin github page for more). You can easily plug in your own generation stuff too. And there’s nifty feature I really like: continuous compilation. In sbt console you write “~ compile” and sbt will run incremental compilation triggered by file changes.

Integrating with IDEA

Some people prefer programming in a text editor. I don’t. So I like IDE integration. Luckily there’s anSBT plugin that generates IDEA project for seamless interaction. You can even run SBT console inside idea for minimal window switching. Usage(from plugin github page): Add the following line to ~/.sbt/plugins/build.sbt or PROJECT_DIR/project/plugins.sbt

addSbtPlugin("com.github.mpeltonen" % "sbt-idea" % "1.2.0")

And then you can use “gen-idea” command in sbt console to generate idea project files.

Integrating with Eclipse

Same story goes for eclipse. Plugin can be found here. To use it: Add sbteclipse to your plugin definition file. You can use either the global one at ~/.sbt/plugins/plugins.sbt or the project-specific one at PROJECT_DIR/project/plugins.sbt:

addSbtPlugin("com.typesafe.sbteclipse" % "sbteclipse-plugin" % "2.1.1")

and to generate project file you use “eclipse” command in sbt console.

Andraž Bajt's blog