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Android Studio, gradle, ndk, aar and the inclusion of several native shared libraries

I pretty much read through almost every question in stackoverflow about the subject.
I browsed documentation and work-notes of other people who are using AS + NDK + gradle to build an aar that would be included by other app.
I was able to build the .so in a different multi-project setup where the structure was different from the one shown in one aspect: it didn't have the first jni/ layer.
I added that extra jni layer so that I'd have a sharedObjectLib#2/ hierarchy. In that jni/ dir, all i have is a single Android.mk whose sole purpose is to include $(call all-subdir-makefiles). After I did that, gradle build reports the NDK failure:
"Error:(89) Android NDK: WARNING: There are no modules to build in this project!"
What I can't seem to be able to do is build multiple shared objects '.so' as part of the aar.
I would really like to know if (a) it is doable; and (b) some pointers to links and/or examples of gradle.build files that actually do that.
Here is the structure I currently have - skipping the usual directories created by Android Studio (v. 1.2.2, btw).
--rootProject/
--build.gradle
--gradle.properties
--local.properties
--settings.gradle
--rootProject.iml
--app/
--moduleProjectThatBuildsAAR/
--build.gradle
--build/
--libs
--src/
--main/
--res/
--AndroidManifest.xml
--jni/
--Android.mk (does include $(call all-subdir-makefiles))
--Application.mk
--sharedObjectLib#1/
--build.gradle
--src/
-- androidTest/
-- main/
--java/
--jni/
-- Android.mk
-- Application.mk
-- *.c and *.h files
--libs/
--obj/
-- build.gradle
It's pretty convoluted and I am hoping the experts would help with simplification.
thanks!

I am using 1.2.2 and found it easy to build the simple NDK projects
from the many tutorials floating around, but frustratingly difficult
to build an NDK project of any complexity. I will summarize what I
found, but I highly suggest reading
this blog
and this StackOverflow.
I found that Android Studio would completely ignore the
Android.mk file I created, and instead auto-generate its own.
To correct this, I had to first hack the build.gradle
script for my project, located at project/app/build.gradle.
You could probably hack the top-level build.gradle, if desired.
This may be what is happening in your case. The auto-generated
Android.mk looks in jni/ for .c source files and finds nothing
there.
This is my build.gradle. I build on a Windows box, so I hacked it for
Windows only. Uncomment the lines if you are using OSX or Linux.
project/app/build.gradle:
//import org.apache.tools.ant.taskdefs.condition.Os
apply plugin: 'com.android.application'
android {
compileSdkVersion 22
buildToolsVersion "22.0.1"
defaultConfig {
applicationId "com.sample.app"
minSdkVersion 15
targetSdkVersion 22
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
//ENABLE CUSTOM ANDROID.MK >>
sourceSets.main.jni.srcDirs= [] //Disable automatic ndk-build.
sourceSets.main.jniLibs.srcDir 'src/main/libs'
//Call regular ndk-build script from app directory
task ndkBuild(type: Exec) {
workingDir file('src/main')
commandLine getNdkBuildCmd()
}
tasks.withType(JavaCompile) {
compileTask -> compileTask.dependsOn { ndkBuild }
}
task cleanNative(type: Exec) {
workingDir file('src/main')
commandLine getNdkBuildCmd(), 'clean'
}
clean.dependsOn cleanNative
}
//ENABLE CUSTOM ANDROID.MK <<
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:22.2.0'
compile 'com.google.android.gms:play-services:7.5.0'
}
//ENABLE CUSTOM ANDROID.MK >>
def getNdkDir() {
if (System.env.ANDROID_NDK_ROOT != null)
return System.env.ANDROID_NDK_ROOT
Properties properties = new Properties()
properties.load(project.rootProject.file('local.properties').newDataInputStream())
def ndkdir = properties.getProperty('ndk.dir', null)
if (ndkdir == null)
throw new GradleException("NDK location not found. Define location with ndk.dir in the local.properties file")
return (ndkdir)
}
def getNdkBuildCmd() {
def ndkbuild = getNdkDir() + "/ndk-build.cmd"
// def ndkbuild = getNdkDir() + "/ndk-build"
// if (Os.isFamily(Os.FAMILY_WINDOWS))
// ndkbuild += ".cmd"
return ndkbuild
}
//ENABLE CUSTOM ANDROID.MK <<

Android Studio NDK Build trouble Error:Execution failed for task ':app:buildNative'

Hi. I'm in Android Studio NDK Build trouble. I've not used native library. just java classes for library use and JNI c or header files.
So I've confused how to write gradle file for my project(saskin library ; I'm studying it).
Please help me~!
Error message
Error:Execution failed for task ':app:buildNative'.
A problem occurred starting process 'command 'C:\NDK/ndk-build''
build.gradle
apply plugin: 'com.android.application'
android {
compileSdkVersion 8
buildToolsVersion "21.1.1"
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
}
}
sourceSets {
main {
jni.srcDirs = []
//jniLibs.srcDir 'src/main/libs'
}
}
defaultConfig {
applicationId "com.sasken.player"
minSdkVersion 8
targetSdkVersion 8
ndk {
moduleName "equalizer"
}
}
// call regular ndk-build(.cmd) script from app directory
task ndkBuild(type: Exec) {
commandLine 'ndk-build', '-C', file('src/main/jni').absolutePath
}
tasks.withType(JavaCompile) {
compileTask -> compileTask.dependsOn ndkBuild
}
}
dependencies {
}

since you're using Windows, you should call ndk-build.cmd instead of ndk-build, from your ndkBuild task.
To make your gradle file work on windows and unix-compatible systems you can modify your task this way:
import org.apache.tools.ant.taskdefs.condition.Os
// call regular ndk-build(.cmd) script from app directory
task ndkBuild(type: Exec) {
if (Os.isFamily(Os.FAMILY_WINDOWS)) {
commandLine 'ndk-build.cmd', '-C', file('src/main').absolutePath
} else {
commandLine 'ndk-build', '-C', file('src/main').absolutePath
}
}
Also, as you're using ndk-build directly, the ndk will generate your libraries inside the libs folder, so you should uncomment jniLibs.srcDir 'src/main/libs' inside your gradle file, in order for your generated libs to be taken in account.

Android Studio Gradle Error - preDexDebug

I recently added a new activity to my android studio project and now I am getting an error when I try and run it. It builds fine but I get the error below when I run it:
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':app:preDexDebug'.
> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
/Applications/Android Studio.app/sdk/build-tools/android-4.4W/dx --dex --output /Users/davidcavanagh/joshcpdandroid/app/build/intermediates/pre-dexed/debug/classes-22ecb8c50fefe43948d87c9fee8e36a6b7d1bb5a.jar /Users/davidcavanagh/joshcpdandroid/app/build/intermediates/exploded-aar/com.android.support/support-v4/20.0.0/classes.jar
Error Code:
1
Here is my build.gradle file
apply plugin: 'com.android.application'
android {
compileSdkVersion 20
buildToolsVersion '20.0.0'
defaultConfig {
applicationId "com.joshcpd.android"
minSdkVersion 15
targetSdkVersion 20
versionCode 1
versionName "1.0"
}
buildTypes {
release {
runProguard false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.google.android.gms:play-services:5.2.08'
compile 'com.android.support:appcompat-v7:20.0.0'
compile project(':libraries:zbar')
}
I have tried removing the supportLappcompat dependency but then I get even more errors. Any help greatly appreciated.

I finally solved this issue by downloading the latest version of gradle.
I still get this error every so often and I just fix it by going to File ----> Invalidate caches/restart
I find Android Studio to be very buggy

Based on where it's trying to find the dx command:
/Applications/Android Studio.app/sdk/build-tools/android-4.4W/dx
it looks like you've crossed a build tools version with something else. The build file you posted in your question looks okay, but look in the other build files in your project (there's at least going to be something in libraries/zbar) and make sure their buildToolsVersion statements are okay. I suspect somewhere you have:
buildToolsVersion 'android-4.4W'
where you should have:
buildToolsVersion '20.0.0'

Now i know the reason of the problem. It was causes by wrong code in \sdk\android-sdk\tools\lib\find_java.bat
Wrong code:
find /i "x86" > NUL && set arch_ext=32 || set arch_ext=64
Correct code:
find /i "x86" > NUL && set arch_ext=32||set arch_ext=64
The wrong code leads to the path of java_exe be
E:\Android\sdk\ANDROI~1\tools\lib\\find_java32 .exe
So, when dx.bat runs
call "%java_exe%" %javaOpts% -Djava.ext.dirs="%frameworkdir%" -jar "%jarpath%" %params%
it will report the wrong status:
Error Code:
1
My platform: win8-32 bit android studio 1.0 - 4GB RAM

I had a similar issue, so I uninstalled the java jdk and reinstalled the latest version from oracle and everything went OK. The link for installing the latest version of jdk is here
Note: you need to update the jdk directory in android studio after doing the above

Can't build project with android-ndk and Android Studio

I have an android project with FFmpeg and other external libraries. I downloaded the latest version of the ndk (ndk-r10) and am running Android Studio 0.8.0. I am also running Windows 8 64bit with the latest version of cygwin.
My project builds without issue and I added the ndk.dir to local.properties. When I try to run I get this error message:
The System cannot find the path specified
Error:Execution failed for task ':app:compileDebugNdk'.
com.android.ide.common.internal.LoggedErrorException: Failed to run command:
C:\Users\John1\AppData\Local\Android\android-ndk-r10\ndk-build.cmd
NDK_PROJECT_PATH=null
APP_BUILD_SCRIPT=C:\Users\John1\AndroidstudioProjects\android-project\app\build\intermediates\ndk\debug\Android.mk
APP_PLATFORM=android-18
NDK_OUT=C:\Users\John1\AndroidstudioProjects\android-project\app\build\intermediates\ndk\debug\obj
NDK_LIBS_OUT=C:\Users\John1\AndroidstudioProjects\android-project\app\build\intermediates\ndk\debug\lib
APP_ABI=all
Error Code:
1
Output:
The system cannot find the path specified.
Looking for advice. Thank you.

with Android Studio, NDK support is preliminary and your *.mk files are ignored.
You can make Android Studio/gradle reuse them by deactivating the default NDK integration, make it call ndk-build(.cmd) by itself, and use standard libs/ location for integrating .so files:
import org.apache.tools.ant.taskdefs.condition.Os
apply plugin: 'android'
android {
compileSdkVersion 19
buildToolsVersion "19.0.3"
defaultConfig{
minSdkVersion 15
targetSdkVersion 19
versionCode 101
versionName "1.0.1"
}
sourceSets.main {
jniLibs.srcDir 'src/main/libs'
jni.srcDirs = [] //disable automatic ndk-build call
}
// call regular ndk-build(.cmd) script from app directory
task ndkBuild(type: Exec) {
if (Os.isFamily(Os.FAMILY_WINDOWS)) {
commandLine 'ndk-build.cmd', '-C', file('src/main').absolutePath
} else {
commandLine 'ndk-build', '-C', file('src/main').absolutePath
}
}
tasks.withType(JavaCompile) {
compileTask -> compileTask.dependsOn ndkBuild
}
}
If you need more information, here is my blog post on this topic: http://ph0b.com/android-studio-gradle-and-ndk-integration/

JNI and Gradle in Android Studio

I'm trying to add native code to my app. I have everything in ../main/jni as it was in my Eclipse project. I have added ndk.dir=... to my local.properties. I haven't done anything else yet (I'm not sure what else is actually required, so if I've missed something let me know). When I try and build I get this error:
Execution failed for task ':app:compileDebugNdk'.
> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
/Users/me/android-ndk-r8e/ndk-build NDK_PROJECT_PATH=null
APP_BUILD_SCRIPT=/Users/me/Project/app/build/ndk/debug/Android.mk APP_PLATFORM=android-19
NDK_OUT=/Users/me/Project/app/build/ndk/debug/obj
NDK_LIBS_OUT=/Users/me/Project/app/build/ndk/debug/lib APP_ABI=all
Error Code:
2
Output:
make: *** No rule to make target `/Users/me/Project/webapp/build/ndk/debug//Users/me/Project/app/src/main/jni/jni_part.cpp',
needed by `/Users/me/Project/app/build/ndk/debug/obj/local/armeabi-v7a/objs/webapp//Users/me/Project/app/src/main/jni/jni_part.o'.
Stop.
What do I need to do?
Android.mk:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
# OpenCV
OPENCV_CAMERA_MODULES:=on
OPENCV_INSTALL_MODULES:=on
include .../OpenCV-2.4.5-android-sdk/sdk/native/jni/OpenCV.mk
LOCAL_MODULE := native_part
LOCAL_SRC_FILES := jni_part.cpp
LOCAL_LDLIBS += -llog -ldl
include $(BUILD_SHARED_LIBRARY)
Application.mk:
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_ABI := armeabi armeabi-v7a
APP_PLATFORM := android-8

Gradle Build Tools 2.2.0+ - The closest the NDK has ever come to being called 'magic'
In trying to avoid experimental and frankly fed up with the NDK and all its hackery I am happy that 2.2.x of the Gradle Build Tools came out and now it just works. The key is the externalNativeBuild and pointing ndkBuild path argument at an Android.mk or change ndkBuild to cmake and point the path argument at a CMakeLists.txt build script.
android {
compileSdkVersion 19
buildToolsVersion "25.0.2"
defaultConfig {
minSdkVersion 19
targetSdkVersion 19
ndk {
abiFilters 'armeabi', 'armeabi-v7a', 'x86'
}
externalNativeBuild {
cmake {
cppFlags '-std=c++11'
arguments '-DANDROID_TOOLCHAIN=clang',
'-DANDROID_PLATFORM=android-19',
'-DANDROID_STL=gnustl_static',
'-DANDROID_ARM_NEON=TRUE',
'-DANDROID_CPP_FEATURES=exceptions rtti'
}
}
}
externalNativeBuild {
cmake {
path 'src/main/jni/CMakeLists.txt'
}
//ndkBuild {
// path 'src/main/jni/Android.mk'
//}
}
}
For much more detail check Google's page on adding native code.
After this is setup correctly you can ./gradlew installDebug and off you go. You will also need to be aware that the NDK is moving to clang since gcc is now deprecated in the Android NDK.
Android Studio Clean and Build Integration - DEPRECATED
The other answers do point out the correct way to prevent the automatic creation of Android.mk files, but they fail to go the extra step of integrating better with Android Studio. I have added the ability to actually clean and build from source without needing to go to the command-line. Your local.properties file will need to have ndk.dir=/path/to/ndk
apply plugin: 'com.android.application'
android {
compileSdkVersion 14
buildToolsVersion "20.0.0"
defaultConfig {
applicationId "com.example.application"
minSdkVersion 14
targetSdkVersion 14
ndk {
moduleName "YourModuleName"
}
}
sourceSets.main {
jni.srcDirs = [] // This prevents the auto generation of Android.mk
jniLibs.srcDir 'src/main/libs' // This is not necessary unless you have precompiled libraries in your project.
}
task buildNative(type: Exec, description: 'Compile JNI source via NDK') {
def ndkDir = android.ndkDirectory
commandLine "$ndkDir/ndk-build",
'-C', file('src/main/jni').absolutePath, // Change src/main/jni the relative path to your jni source
'-j', Runtime.runtime.availableProcessors(),
'all',
'NDK_DEBUG=1'
}
task cleanNative(type: Exec, description: 'Clean JNI object files') {
def ndkDir = android.ndkDirectory
commandLine "$ndkDir/ndk-build",
'-C', file('src/main/jni').absolutePath, // Change src/main/jni the relative path to your jni source
'clean'
}
clean.dependsOn 'cleanNative'
tasks.withType(JavaCompile) {
compileTask -> compileTask.dependsOn buildNative
}
}
dependencies {
compile 'com.android.support:support-v4:20.0.0'
}
The src/main/jni directory assumes a standard layout of the project. It should be the relative from this build.gradle file location to the jni directory.
Gradle - for those having issues
Also check this Stack Overflow answer.
It is really important that your gradle version and general setup are correct. If you have an older project I highly recommend creating a new one with the latest Android Studio and see what Google considers the standard project. Also, use gradlew. This protects the developer from a gradle version mismatch. Finally, the gradle plugin must be configured correctly.
And you ask what is the latest version of the gradle plugin? Check the tools page and edit the version accordingly.
Final product - /build.gradle
// Top-level build file where you can add configuration options common to all sub-projects/modules.
// Running 'gradle wrapper' will generate gradlew - Getting gradle wrapper working and using it will save you a lot of pain.
task wrapper(type: Wrapper) {
gradleVersion = '2.2'
}
// Look Google doesn't use Maven Central, they use jcenter now.
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:1.2.0'
// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
}
allprojects {
repositories {
jcenter()
}
}
Make sure gradle wrapper generates the gradlew file and gradle/wrapper subdirectory. This is a big gotcha.
ndkDirectory
This has come up a number of times, but android.ndkDirectory is the correct way to get the folder after 1.1. Migrating Gradle Projects to version 1.0.0. If you're using an experimental or ancient version of the plugin your mileage may vary.

gradle supports ndk compilation by generating another Android.mk file with absolute paths to your sources.
NDK supports absolute paths since r9 on OSX, r9c on Windows, so you need to upgrade your NDK to r9+.
You may run into other troubles as NDK support by gradle is preliminary. If so you can deactivate the ndk compilation from gradle by setting:
sourceSets.main {
jni.srcDirs = []
jniLibs.srcDir 'src/main/libs'
}
to be able to call ndk-build yourself and integrate libs from libs/.
btw, you have any issue compiling for x86 ? I see you haven't included it in your APP_ABI.

In my case, I'm on Windows and following the answer by Cameron above only works if you use the full name of the ndk-build which is ndk-build.cmd. I have to clean and rebuild the project, then restart the emulator before getting the app to work (Actually I imported the sample HelloJni from NDK, into Android Studio). However, make sure the path to NDK does not contain space.
Finally, my build.gradle is full listed as below:
apply plugin: 'com.android.application'
android {
compileSdkVersion 21
buildToolsVersion "21.1.2"
defaultConfig {
applicationId "com.example.hellojni"
minSdkVersion 4
targetSdkVersion 4
ndk {
moduleName "hello-jni"
}
testApplicationId "com.example.hellojni.tests"
testInstrumentationRunner "android.test.InstrumentationTestRunner"
}
sourceSets.main {
jni.srcDirs = [] // This prevents the auto generation of Android.mk
// sourceSets.main.jni.srcDirs = []
jniLibs.srcDir 'src/main/libs' // This is not necessary unless you have precompiled libraries in your project.
}
task buildNative(type: Exec, description: 'Compile JNI source via NDK') {
def ndkDir = android.plugin.ndkFolder
commandLine "$ndkDir/ndk-build.cmd",
'-C', file('src/main/jni').absolutePath, // Change src/main/jni the relative path to your jni source
'-j', Runtime.runtime.availableProcessors(),
'all',
'NDK_DEBUG=1'
}
task cleanNative(type: Exec, description: 'Clean JNI object files') {
def ndkDir = android.plugin.ndkFolder
commandLine "$ndkDir/ndk-build.cmd",
'-C', file('src/main/jni').absolutePath, // Change src/main/jni the relative path to your jni source
'clean'
}
clean.dependsOn 'cleanNative'
tasks.withType(JavaCompile) {
compileTask -> compileTask.dependsOn buildNative
}
}
dependencies {
compile 'com.android.support:support-v4:21.0.3'
}

Android Studio 2.2 came out with the ability to use ndk-build and cMake. Though, we had to wait til 2.2.3 for the Application.mk support. I've tried it, it works...though, my variables aren't showing up in the debugger. I can still query them via command line though.
You need to do something like this:
externalNativeBuild{
ndkBuild{
path "Android.mk"
}
}
defaultConfig {
externalNativeBuild{
ndkBuild {
arguments "NDK_APPLICATION_MK:=Application.mk"
cFlags "-DTEST_C_FLAG1" "-DTEST_C_FLAG2"
cppFlags "-DTEST_CPP_FLAG2" "-DTEST_CPP_FLAG2"
abiFilters "armeabi-v7a", "armeabi"
}
}
}
See http://tools.android.com/tech-docs/external-c-builds
NB: The extra nesting of externalNativeBuild inside defaultConfig was a breaking change introduced with Android Studio 2.2 Preview 5 (July 8, 2016). See the release notes at the above link.

My issue on OSX it was gradle version. Gradle was ignoring my Android.mk.
So, in order to override this option, and use my make instead, I have entered this line:
sourceSets.main.jni.srcDirs = []
inside of the android tag in build.gradle.
I have wasted lot of time on this!

In the module build.gradle, in the task field, I get an error unless I use:
def ndkDir = plugins.getPlugin('com.android.application').sdkHandler.getNdkFolder()
I see people using
def ndkDir = android.plugin.ndkFolder
and
def ndkDir = plugins.getPlugin('com.android.library').sdkHandler.getNdkFolder()
but neither of those worked until I changed it to the plugin I was actually importing.