How to specify external C++ source folders for Android NDK with Gradle

Issue

I want to add some C++ source files to my Android Studio project that are not in the project tree. I'm new to Gradle, and tried to research this as much as possible. From what I read, the following build.gradle file should work, but it doesn't. The bit about jni.sourceDirs came from this post: http://www.shaneenishry.com/blog/2014/08/17/ndk-with-android-studio/

Is this the right approach?

apply plugin: 'com.android.application'

android {
    compileSdkVersion 22
    buildToolsVersion "22.0.1"
    defaultConfig {
        applicationId "com.mycompany.myapp"
        minSdkVersion 22
        targetSdkVersion 22

        ndk {
            moduleName "mymodule"
            ldLibs "log"
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
        }
    }

    sourceSets.main {
        jni.srcDirs '../external/source/dir'
    }
}

Solution

Have a look at my article about this: http://www.sureshjoshi.com/mobile/android-ndk-in-android-studio-with-swig/

There are two things you need to know here. By default, if you have external libs that you want loaded into the Android application, they are looked for in the (module)/src/main/jniLibs. You can change this by using setting sourceSets.main.jniLibs.srcDirs in your module’s build.gradle. You’ll need a subdirectory with libraries for each architecture you’re targeting (e.g. x86, arm, mips, arm64-v8a, etc…)

The code you want to be compiled by default by the NDK toolchain will be located in (module)/src/main/jni and similarly to above, you can change it by setting sourceSets.main.jni.srcDirs in your module’s build.gradle

And a sample Gradle file from that page:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "21.1.2"

    defaultConfig {
        applicationId "com.sureshjoshi.android.ndkexample"
        minSdkVersion 15
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"

        ndk {
            moduleName "SeePlusPlus" // Name of C++ module (i.e. libSeePlusPlus)
            cFlags "-std=c++11 -fexceptions" // Add provisions to allow C++11 functionality
            stl "gnustl_shared" // Which STL library to use: gnustl or stlport
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

Also, when specifying external to the /jni directory, try using the full build path (using one of the macros, eg):

'${project.buildDir}/../../thirdParty/blah/blah/'

Answered By - SJoshi