Monday, November 14, 2011

Installing dependencies on the device

This last two weeks I have been giving it a try to Scala on Android. While learning how to do it, I found something interesting I would like to share.

Developing Android apps using scala

The big problem of developing in Scala is that Android doesn't provide a way to install dependencies on the device. So, if you want to use Scala you need to place the scala's jar in your apk.

Placing the scala jar inside the apk bring another problem, apk size. To fix this, scala developers use proguard to remove all unused classes from the scala jar.

Using proguard to remove unused classes works like charm but it brings a third problem. Compilation time. For me, it takes a whole minute to compile an application with a single Activity coded in scala.

Coding scala in Android is as frustrating as testing android apps :)

While looking for a solution for this, I asked a question in stackoverflow and it was answered by @jberkel. He pointed me to a project called scala-android-libs created by Johannes Rudolph.

What this project does is very interesting. It installs the scala's jars in a rooted device and allows the application to use it through the AndroidManifest tag uses-library.

How does it work?

It creates a serie of XMLs in /system/etc/permissions that look like this:

file="/data/data/" />

This means that if inside the AndroidManifest the app says:

It will be able to use the scala_actors.jar file inside the /data/data/ folder as a dependency.

Since now we have the jar installed in our device, we can avoid the proguard step and the build times are very similar to build an ordinary java app.

Taking it further
Every time I develop an android application I start creating a maven project because I know that I will use certain dependencies. After learning about this approach I thought about leaving my dependencies inside the device.

Why don't extending scala-android-libs approach to provide a way to manage dependencies inside the device to make the build times faster?
Perhaps having an android app that allows to install/remove jar files and automatically generate this XMLs with the proper permissions.

What do you think?
Would you use it?

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