Loading shared library in Android using RubyMotion

Problem

Using a vendor library may require to load a shared library (a.k.a .so) along with it to make it work.

I faced this problem when I was trying to use Android PDFView which relies on VuDroid to display PDFs in an Android app.

At the beginning I just added the android-pdfview-1.0.2.jar file in the vendor directory then used it in my Rakefile:

app.vendor_project jar: 'vendor/android-pdfview-1.0.2.jar'

It was compiling and all seems to be ok until I got to the screen where I used an Android PDFView. Trying to display a PDF was throwing an exception:

Caused by: java.lang.UnsatisfiedLinkError: Couldn't load vudroid from loader dalvik.system.PathClassLoader[DexPathList[[zip file "/data/app/com.company.awesome_app.apk"],nativeLibraryDirectories=[/data/app-lib/com.company.awesome_app-1, /vendor/lib, /system/lib]]]: findLibrary returned null

Clearly vudroid shared library can’t be found.

Android PDFView doesn’t bundle vudroid shared library. It’s up to you to get it and load it in your app. That’s why it’s available in Android PDFView repo.

This is the armeabi version which is of interest to us. For now this is the only architecture supported by RubyMotion.

Solution

If you were using the classical Java toolbelt you would just put this file in your lib directory and you would be good to go.

In RubyMotion you can’t do that. You have to specify the dependency on the shared library in your Rakefile.

Sadly this option isn’t mentioned anywhere in the RubyMotion documentation for Android, that’s why I’m writing this post and you’ll see it’s really easy to load a shared library.

Back to your Rakefile, you’ll have to do this:

app.vendor_project jar: 'vendor/android-pdfview-1.0.2.jar', native: ["vendor/armeabi/libvudroid.so"]

As you can see, I dropped the .so file in vendor/armeabi directory. The armeabi bit is required by RubyMotion. It considers the shared library useable only if it’s the armeabi version and relies on its name to check it.

You’re now good to go, you can rake device and the shared library will be loaded along with the jar. The runtime exception will be gone.

Good PDF viewing ;-)