Building shared with static library dependency

Question

I'm trying to build a shared library using NDK. My folder structure has two folders, one written in C++ (the core) and one written in Java, called project, which is an Android Studio project. The C++ library is compiled fine and the .a file is generated, but then it's not linking with the shared library. Here's my build.gradle:

buildscript {

    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.3.0'
        classpath 'net.sf.proguard:proguard-gradle:5.2.1'
    }
}

apply plugin: 'android-library'

android {

    compileSdkVersion 16
    buildToolsVersion "23.0.1"

    defaultConfig {
        minSdkVersion 16
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"

        ndk {
            moduleName "core"
            cFlags "-std=c++11 -fexceptions -I../core/includes"
            stl "stlport_shared"
        }
    }

    sourceSets {
        main {
            manifest.srcFile 'AndroidManifest.xml'
            jniLibs.srcDir 'libs'
            jni.srcDirs = ['src/main/jni', 'src/main/jni/', 'jni/']
        }
    }

    task buildNative(type: Exec, description: 'Compile JNI source via NDK') {
        def ndkDir = plugins.getPlugin('com.android.library').sdkHandler.getNdkFolder()
        commandLine "$ndkDir/ndk-build",
                '-C', file('jni').absolutePath,
                '-j', Runtime.runtime.availableProcessors(),
                'all',
                'NDK_DEBUG=1'
    }

    task cleanNative(type: Exec, description: 'Clean JNI object files') {
        def ndkDir = plugins.getPlugin('com.android.library').sdkHandler.getNdkFolder()
        commandLine "$ndkDir/ndk-build",
                '-C', file('jni').absolutePath,
                'clean'
    }

    task cleanBinaryFolders(type: Delete, description: 'Clean binary folders') {
        delete 'libs', 'obj'
    }

    clean.dependsOn 'cleanNative'
    clean.dependsOn 'cleanBinaryFolders'

    tasks.withType(JavaCompile) {
        compileTask -> compileTask.dependsOn buildNative
    }
}

dependencies {
    compile 'com.android.support:support-v4:20.0.0'
}

Here's my Android.mk:

SHELL = /bin/bash

MY_HOMEDIR = $(realpath $(shell pwd)/../..)
MY_COREDIR = $(MY_HOMEDIR)/core
MY_ANDROIDDIR = $(MY_HOMEDIR)/project

MY_CORESOURCES = $(shell find $(MY_COREDIR)/src -type f -name "*.cpp")
MY_BRIDGESOURCES = $(shell find $(MY_ANDROIDDIR)/jni -type f -name "*.cpp")

LOCAL_PATH = $(MY_HOMEDIR)

# Generate a static library from the core implementation
include $(CLEAR_VARS)
LOCAL_MODULE = core
LOCAL_SRC_FILES = $(MY_CORESOURCES)
TARGET_PLATFORM = android-16
TARGET_ARCH_ABI = all
LOCAL_C_INCLUDES = $(MY_COREDIR)/includes
#LOCAL_LDLIBS = -llog
LOCAL_CFLAGS = -llog -I$(MY_COREDIR)/includes
include $(BUILD_STATIC_LIBRARY)

include $(CLEAR_VARS)
LOCAL_MODULE = project
LOCAL_SRC_FILES = $(MY_BRIDGESOURCES)
TARGET_PLATFORM = android-16
TARGET_ARCH_ABI = all
LOCAL_STATIC_LIBRARIES = core
LOCAL_C_INCLUDES = $(MY_COREDIR)/includes
LOCAL_LDLIBS = -lcore # I’m not sure about this
LOCAL_CFLAGS = -llog -I$(MY_COREDIR)/includes
include $(BUILD_SHARED_LIBRARY)

When compiling like this I get a bunch of undefined reference errors, even though the methods are implemented by the core module. What am I missing?

Answer 1

https://stackoverflow.com/a/22401410/755804 reads:

Only use LOCAL_LDLIBS for system library dependencies. If you want to point to another library, it's much better to list them in either LOCAL_STATIC_LIBRARIES and LOCAL_SHARED_LIBRARIES (even if this means defining a PREBUILT_XXX module for them), because this lets the build system work out dependencies and ordering automatically for you.