在Android Studio中创建本机库

Question

I have created android studio project with c++ support and installed native development kit and other required tools. How to import another prebuilt native library to include in c++ code. I want to do something like this

I have edited cmakelist.txt as given below and now it show shared library under cpp folder.

cmake_minimum_required(VERSION 3.4.1)
set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../distribution)
add_library(lib_gmath STATIC IMPORTED)
set_target_properties(lib_gmath PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/gmath/lib/${ANDROID_ABI}/libgmath.a)
add_library(lib_gperf SHARED IMPORTED)
set_target_properties(lib_gperf PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/gperf/lib/${ANDROID_ABI}/libgperf.so)
add_library(lib_ocr SHARED IMPORTED)
set_target_properties(lib_ocr PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/ocr/lib/${ANDROID_ABI}/libLPROCR.so)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
add_library(hello-libs SHARED
        hello-libs.cpp)
target_include_directories(hello-libs PRIVATE
                       ${distribution_DIR}/gmath/include
                       ${distribution_DIR}/gperf/include)
target_link_libraries(hello-libs
                  android
                  lib_gmath
                  lib_gperf
                  lib_ocr
                  log)

But i am not able to include classes from that prebuilt library in my c++ code.

Answer 1

There are few things that I should mention here.

1. I suggest to switch to gradle+clang for building your code. Android.mk is somehow getting old and it is better to use newer build systems if you are starting new project.
2. Make sure that your prebuilt library can be used in android. If it is not, you need to build it first. For example I built openssl myself because I could not find a suitable prebuilt library.

In case your are using gradle+cmake , here is a simple CMakeLists.txt file for your prebuilt libraries:

cmake_minimum_required(VERSION 3.4.1)

add_library( core-api
             SHARED
             src/main/cpp/mysource.c )

# prebuilt libraries

add_library( crypto-lib
             STATIC
             IMPORTED )

set_target_properties( crypto-lib
                       PROPERTIES IMPORTED_LOCATION
                       ${CMAKE_CURRENT_SOURCE_DIR}/../prebuilt/crypto/${ANDROID_ABI}/lib/libcrypto.a )


include_directories( src/main/cpp/
                     ../prebuilt/crypto/common/include/
                     ../prebuilt/crypto/${ANDROID_ABI}/include/ )

# other libraries

find_library( log-lib
              log )

target_link_libraries( core-api
                       crypto-lib
                       ${log-lib} )

And this is a gradle file that uses this CMakeLists.txt :

apply plugin: 'com.android.library'

android {
    compileSdkVersion rootProject.ext.sdkVersion

    defaultConfig {
        minSdkVersion 14
        targetSdkVersion 27

        externalNativeBuild {
            cmake {
                arguments "-DANDROID_TOOLCHAIN=clang", "-DANDROID_STL=c++_static"
                cFlags "-D__STDC_FORMAT_MACROS", "-fno-integrated-as"
            }
        }

        ndk {
            abiFilters "armeabi-v7a", "arm64-v8a", "x86", "x86_64"
        }
    }

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

        debug {
            externalNativeBuild {
                cmake {
                    cFlags "-Wall","-DDEBUG"
                }
            }

            debuggable true
        }
    }

    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

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