How should I use R queries in an Android Studio application project to be able to easily convert the project into library project later?

Question

The question have basically two parts, because answers can "deactivate" other questions: Can I use android application projects (written in Android Studio) in a Unity game engine project somehow? If yes, the questions below are not important, but I think the answer is no.

There are Android java developers, and there are Unity game engine c# developers in here. Some of us need to create an Android Studio application project, and they should have some kind of visual surface for that during the debugging. After this, it would be better if they would be able to give the code to us as a library project, because a jar file should be created for the Unity, because the final surface of the app will be in Unity.

I know there are topics about "how to convert an application project into library project", and they works perfectly in a simple example project. But this can't be made easily, if the R method and R variable calls (or I don't know the name of that, R.id.something and R.something, etc.) are in a lot of java files. It's a lot of work cutting them out. I simply can't build the library app, if it has these R things in them. It was the case in a big Android application project, but I don't know if there would be a good workflow idea for a new project.

Since I'm not an android developer, I don't know how should this workflow in a new project to be made easily. Any idea?

Answer 1

The "R" in android development refers to the R class used to access the res folder in an android project, wich contains all other resources needed (images, layouts, strings)

Unity allows you to access native and custom plugins that you can import to your editor, I recomend giving a good read to the official documentation to Plugins for android in the unity website
https://docs.unity3d.com/Manual/PluginsForAndroid.html

The Android plugin mechanism also allows Java to be used to enable interaction with the Android OS.
There are several ways to create a Java plugin but the result in each case is that you end up with a .jar file containing the .class files for your plugin. One approach is to download the JDK, then compile your .java files from the command line with javac. This will create .class files which you can then package into a .jar with the jar command line tool.