CMake: Android Studio native activity project cannot find thirdparty lib outside the project root

Question

For incorporating other opensource libs via CMake, I've checked similar questions such as this one:

Android Studio: Adding a library outside of the project root

but those are about incorporating Android-Studio lib projects instead of external libs.

In my case, I have a folder structure like this:

• thirdparty
  • category
    • MyLib
• src
  • MyAndroidStudioProject
    • build.gradle
    • settings.gradle
    • ...
    • app
      • build
      • libs
      • src
      • build.gradle
      • ...

In the project CMakeLists.txt, I then added this

target_link_libraries( # Specifies the target library.
        native-lib

        # Links the target library to the log library
        # included in the NDK.
        ${log-lib} MyLib)

set (MyLib_DIR ../../../thirdparty/category/MyLib)

# output lib binary
add_subdirectory (${MyLib_DIR} ./MyLib) 

include_directories (${OBOE_DIR}/include)

I learned from sample code and assume that the CMake source root is at src/MyAndroidStudioProject/app, so MyLib is located using relative path accordingly.

However, building the project gives me

CMake Error at /path/to/src/MyAndroidStudioProject/app/src/main/cpp/CMakeLists.txt:53 (add_subdirectory):
add_subdirectory given source "../../../thirdparty/category/MyLib"
which is not an existing directory.

How should I fix this? Should I configure other settings in the project?

Answer 1

OK, solved it myself.

The relative path should be relative to the CMakeLists.txt file, located at

/path/to/src/MyAndroidStudioProject/app/src/main/cpp/CMakeLists.txt

So the correct relative path in my case should be

set (MyLib_DIR ../../../../../../thirdparty/category/MyLib)

i.e., CMakeLists.txt is 3 levels down the app folder.