CMAKE not obeying flags from gradle for NDK building on Android

Question

I have an Android NDK project which I am trying to build through Gradle+CMake.

build.gradle:

apply plugin: 'com.android.library'

allprojects {
    repositories {
        jcenter()
        google()
    }
}

android {
    compileSdkVersion 27
    defaultConfig {
        minSdkVersion 16
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11"
                arguments "-DANDROID_ABI=armeabi-v7a",
                          "-DANDROID_PLATFORM=android-16",
                          "-DANDROID_STL=gnustl_static",
                          "-DANDROID_CPP_FEATURES=rtti exceptions",
                          "-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=libs"
            }
        }
    }

    buildTypes {
        release {
            ndk {
                abiFilters "armeabi-v7a"
            }
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
        debug {
            ndk {
                abiFilters "armeabi-v7a"
            }
        }
    }
    externalNativeBuild {
        cmake {
            path 'CMakeLists.txt'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
}

CMAKE Command Output:

Executable : /Users/ssk/Library/Android/sdk/cmake/3.6.3155560/bin/cmake
arguments : 
-H/Users/ssk/MyProject
-B/Users/ssk/MyProject/.externalNativeBuild/cmake/debug/armeabi-v7a
-DANDROID_ABI=armeabi-v7a
-DANDROID_PLATFORM=android-16
------> -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=/Users/ssk/MyProject/build/intermediates/cmake/debug/obj/armeabi-v7a
-DCMAKE_BUILD_TYPE=Debug
-DANDROID_NDK=/Users/ssk/Library/Android/sdk/ndk-bundle
-DCMAKE_CXX_FLAGS=-std=c++11
-DCMAKE_TOOLCHAIN_FILE=/Users/ssk/Library/Android/sdk/ndk-bundle/build/cmake/android.toolchain.cmake
-DCMAKE_MAKE_PROGRAM=/Users/ssk/Library/Android/sdk/cmake/3.6.3155560/bin/ninja
-GAndroid Gradle - Ninja
-DANDROID_STL=gnustl_static
-DANDROID_ABI=armeabi-v7a
-DANDROID_PLATFORM=android-16
-DANDROID_CPP_FEATURES=rtti exceptions
------> -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=libs
jvmArgs : 

I am trying to configure the output directory using DCMAKE_LIBRARY_OUTPUT_DIRECTORY, but it's not obeying.

Gradle prefixes a default one before my option as highlighted (------> in cmake command output).

Question:

How should I configure the output directory?

Answer 1

Below snippet will configure your output directory:

For static lib output directory, try below:

# copy out the static lib binary 
set_target_properties(${STATIC_LIBRARY_NAME}
                      PROPERTIES
                      ARCHIVE_OUTPUT_DIRECTORY "libs/${ANDROID_ABI}")

For shared lib output directory, try below:

# copy out the shared lib binary 
set_target_properties(${SHARED_LIBRARY_NAME}
                      PROPERTIES
                      LIBRARY_OUTPUT_DIRECTORY "libs/${ANDROID_ABI}")

Explanation:

ANDROID_ABI is a variable defining the Android ABI, e.g. armeabi-v7a

Reference about the CMake variables definition:

Android NDK path variable for "strip" command in CMake build tool chain

Answer 2

Probably you need to set the buildStagingDirectory option. In the next link you will find how to manage paths for CMake in gradle:

CMakeOptions

And as a side note unrelated to the question. In your gradle script seems you are still using gnustl_static which is no longer supported and will be removed in the next NDK versions. You should switch to either c++_static or c++_shared. Take into account that gcc has been deprecated and you should use clang. Next an example:

externalNativeBuild {
            cmake {
                arguments "-DANDROID_PLATFORM=android-16", "-DANDROID_STL=c++_static", "-DANDROID_TOOLCHAIN=clang"
                abiFilters "armeabi-v7a", "arm64-v8a", "x86"
            }
        }