Android NDK Setting

1. app/src/main 하위에 jni 폴더 생성

 

 

2. "javah" External Tools 설정

javah는 java 10 버전부터 없어졌다고 하니, jdk 8 버전을 설치합니다.

Program: /Library/Java/JavaVirtualMachines/jdk1.8.0_202.jdk/Contents/Home/bin/javah

Arguments: -classpath "$ContentRoot$/src/main/java" -v -jni "$FileClass$"

Working directory: "$ContentRoot$/src/main/jni"

 

 

3. Module Main에 loadLibrary 코드 작성

 

 

4. 헤더파일 생성

2단계에서 설정한 javah 명령어를 이용하여 헤더파일 생성 --> jni 디렉터리 하위에 메인모듈에 작성한 jni 코드를 바탕으로 헤더파일이 생성됩니다.

 

 

5. cpp 코드 작성

 

 

6. CMakeLists.txt 파일 작성

기본 틀은 다음과 같습니다.

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.10.2)

set( CPP_FILES
        myfirstNDK.cpp)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.
add_library( # Sets the name of the library.
             myfirstndk

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             ${CPP_FILES} )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.
target_link_libraries( # Specifies the target library.
                       myfirstndk

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

                       android)

 

 

7. build.gradle(:app) 설정

ndkVersion 명시합니다.(ndk 버전은 SDKManager --> SDK Tools 탭에서 확인 가능)

android{ defaultConfig { externalNativeBuild { ... }}} 에서 cmake의 version 등을 명시합니다.

android{ externalNativeBuild { ... }} 에서 "CMakeLists.txt" 파일의 위치를 명시합니다.

plugins {
    id 'com.android.application'
}

android {
    compileSdk 30
    // ndk version 명시
    ndkVersion "23.0.7599858"

    defaultConfig {
        ...
        // externalNativeBuild 블록 안에서 cmake version, cppFlags, arguments 등 설정 가능
        externalNativeBuild {
            cmake {
                version "3.18.1"
//                cppFlags "-std=c++11", "-Wall"
//                arguments "-DANDROID_STL=c++_static", "-DANDROID_ABI=arm64-v8a"
            }
        }
    }

    buildTypes {
        ...
    }
    compileOptions {
        ...
    }
    // Use this block to link gradle to your CMakeLists.txt file. only 'path' variable is valid here
    externalNativeBuild {
        cmake {
            path "src/main/jni/CMakeLists.txt"
        }
    }
}

...

 

※ 특정 ABI(Application Binary Interface)를 위한 코드 생성

출처: https://developer.android.com/ndk/guides/abis#gc

android {
    defaultConfig {
        ndk {
            abiFilters 'arm64-v8a'
        }
    }
}

 

 

8. 빌드 및 검사

(빌드)Build --> Make Project

(검사)Build --> Analyze APK. apk파일안에 빌드한 .so파일이 들어가있는지 확인합니다

 

 

※ 출처

https://question0.tistory.com/39 (기존 프로젝트에 NDK 설정)

https://math-coding.tistory.com/177 (NDK 프로젝트 예제)

https://web-inf.tistory.com/98 (NDK 프로젝트 상세한 예제)

https://github.com/android/ndk-samples (안드로이드 NDK 샘플 예제)

https://medium.com/@jrejaud/modern-android-ndk-tutorial-630bc11829a2 (Modern Android NDK Tutorial)

https://github.com/hankyojeong/Android-NDK_Study(안드로이드 NDK 스터디)