Code sharing in Android Studio

Question

I have started working on a project where I will need to share a bunch of Java classes across a bunch of apps. In Eclipse it was possible to create one project with all such classes and use it as a library in a workspace with all your dependent projects, but in Android Studio it doesn't seem possible to do so (At least not easily).

I have been reading a bunch of posts and a lot of them suggest setting up a library project, generating an aar file and then using that in my projects. But, as I understand it, this will make my library open-source (Am I right?), which I don't want. I am doing this for a client and I want the code base to be private.

Also, I know that a module can be imported into a new project. But this creates a COPY of the original module. This is not what I want at all. I don't wanna maintain multiple copies of the same classes, which completely defeats the purpose of 'code sharing'.

Is there any good way of achieving what I am looking for? Any help is appreciated.

Answer 1

You have a couple different options.

One option is to maintain your libraries as separate projects and compile them to an archive format, such as JAR or AAR; JAR files are for pure Java libraries, and AAR is for Android libraries (which contain code that accesses Android APIs and/or has Android resources). As was pointed out in the comments, AAR doesn't force you to publish your code to the world any more than JAR files would; it's just an archive file format whose files can be local to your machine or your organization.

With that archive file in hand, you can include it in other projects. If you're part of a multi-developer organization, you may find it convenient to use a repository manager to publish and maintain those libraries within your organization, and you can use Maven coordinate-style specs to include libraries in your projects, which you don't have to manually copy over to your development machine.

The disadvantage of this approach is that it makes it a little harder to make changes to those libraries: you need to load up the project, make changes, build an archive, and distribute the archive.

The other approach is to keep the library as a source module like you did in Eclipse. You observed that Android Studio will make a copy of the module if you import it via UI, but if you bypass the UI and modify the build scripts directly, you can do what you want, which is to use the module in-place and share a single copy among multiple projects. To do this, work in your settings.gradle file and add this:

include ':module_name'
project(':module_name').projectDir = new File(settingsDir, '../relative/path/to/module')

I would strongly encourage you to not use a pure relative path here; in this example, the path is anchored to the settingsDir variable supplied by Gradle, which is defined to be the directory where settings.gradle is found. If you use a pure relative path (i.e isn't anchored to anything), you're dependent on the working directory being the same in all environments where the build file is run (command line vs. Android Studio vs. CI server), which isn't a good thing to assume.