Using AndroidStudio + gradle + NDK to build Library for Android and Linux

Question

I want to build a shared library with different variants / versions that I can use on Android and in Linux applications.

Therefor, I set up an Android Project consisting of an app module and a (native C/C++) library module as outlined in the official Android Studio documentation ^* , so that my complete build tool chain for the library consists of ^** :

• Android Studio
• gradle / build.gradle
• cmake / CMakeLists.txt
• ninja
• clang

My code is actually portable, eg I used #ifdef __ANDROID__ around Android specific code paths, and I can compile a working Linux shared object by hand , that is, by invoking the compiler from the command line.

Is there a nice way to use the above tool chain to create both the .so files for Android and Linux, without maintaining two redundant sets of build configuration files?

_{* I followed the documentation from May 2017, which is almost identical to this archive.org snapshot from February 2017.}

_{** I do not use Android.mk and ndk-build, so that this related question does not apply for me, even though the purpose is the same.}

Answer 1

As it turns out, it's easier than I thought. In this case, Gradle is not needed for the Linux version, and the Cmake configuration is mostly portable across Android and Linux. So theoretically, you can just:

cd $AndroidProject/librarymodule/build
cmake -G "Unix Makefiles" .. && make

As said before, this circumvents gradle, meaning that the configurations in the build.gradle are nerver applied.

The easiest fix is to add those settings to CMakeLists.txt like this:

# (...) Common defintions for both platforms here (...)

if (ANDROID)
    find_library( log-lib log )
    target_link_libraries( librarymodule ${log-lib} )
else ( )
    find_package( OpenCV REQUIRED )
    target_compile_definitions ( librarymodule PUBLIC ENABLE_DEBUG_LOGGING linux HAVE_LIBUDEV)
    target_include_directories ( librarymodule PRIVATE  src/main/cpp ../otherlib/src/main/cpp )
    target_compile_options ( librarymodule PRIVATE -Wall -Wno-unknown-pragmas -O0 -g -std=c++11 -fexceptions )
    target_link_libraries( librarymodule pthread ${OpenCV_LIBS} )
)

Theres a disadvantage in having identical / similar settings scattered across build.grade for Android and CMakeLists.txt for Linux. Possible solutions:

• Move all those settings into CMakeLists.txt . Should be trivial.
• Try to use Gradle as a wrapper for both Android and Linux and move all settings to build.gradle . Could be complex.

Answer 2

I searched for a similar solution, but I think there is currently no way to do it. There is no Android-Studio plugin to do native c/c++ compilation. Java is possible, but not an option for me.