前言：

本人一直在做图像识别、人脸识别、人脸疾病检测等相关算法工作。一般Windows下封装成dll动态库，Linux下封装成SO共享库。Android就使用 NDK技术封装成支持ARM平台的SO库。

我使用的版本是Android Studio 3.4.1、OpenCV-4.2.0、Dlib-19.18。

一. 前期准备

1.1. OpenCV及Dlib库下载

1）从OpenCV官网https://opencv.org/releases/ 下载Android版本并解压。

2）从Dlib 官网http://dlib.net/ 下载dlib-19.18版本并解压。

1.2. 创建项目

打开Android Studio创建支持Native C++的项目，选择支持java，然后选择支持c++ 14新特性，，点击Finish创建项目。

1.3. 拷贝依赖库

1）在"src/main/cpp"目录下创建四个包”common"、"include"、"libs"、"source"。（"common"用来存放公共工具类，"include"用于存放依赖库的包含目录，即opencv和dlib库的头文件。"libs"用来存放静态库文件，“source"主要放C++源代码）将"CMakeLists.txt"文件移动到app目录下，移动后需要修改“build.gradle"中的"CMakeLists.txt"文件路径。这里也可以不移动，只是自己试的不移动的话会遇到一些问题。更改前为：

    externalNativeBuild {        cmake {            path "src/main/cpp/CMakeLists.txt"            version "3.10.2"        }    }

更改后为：

    externalNativeBuild {        cmake {            path "CMakeLists.txt"            version "3.10.2"        }    }

2) 将解压后的"../OpenCV-android-sdk/sdk/native"目录下的libs文件夹拷贝到"src/main/cpp/libs"目录下，并重命名为"opencv2"；

3) 将解压后的"../OpenCV-android-sdk/sdk/native/jni/include"目录下的opencv2文件夹拷贝到"src/main/cpp/include"目录下。

4) 将解压后的Dlib目录下的"../dlib"文件夹拷贝到"src/main/cpp/include"目录下。

common目录放的是JNI公共工具类，主要处理Andord 位图Bitmap到OpenCV Mat数据的转换，这个内容这里就先不介绍，后续博客会介绍这些。添加前后的代码结构对比如下图：

二. 环境配置

2.1. 导入OpenCV库

打开项目，然后依次"File---> New ---> Import Module"，然后打开OpenCV-android-sdk解压目录下的"../sdk/java"文件

Module Name更改为"OpenCVLibrary420"，然后依次点击"Next"、"Finish"。在项目中会添加"OpenCVLibrary420"的包名。

2.2. 修改"OpenCVLibrary420"的"build.grade"

需要将"OpenCVLibrary420"改成以库的方式存在，然后修改版本号和app的build.grade文件版本号一样。附上我的"build.grade"内容。注意这块内容的修改很关键。

//apply plugin: 'com.android.application'(原始内容)apply plugin: 'com.android.library'      //添加内容android {    //compileSdkVersion 28    //buildToolsVersion "28.0.3"    //更改编译版本和app的build.grade一样    compileSdkVersion 29       buildToolsVersion "29.0.2"    defaultConfig {        //applicationId "org.opencv"    // 原有内容        // 添加内容,是从app的build.grade中拷贝过来，要保持一致        minSdkVersion 15        targetSdkVersion 29    }    buildTypes {        release {            minifyEnabled false            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'        }    }}

2.3. app添加依赖"OpenCVLibrary420"包

打开"File --> Project Structure-->Dependencies",然后点击"app, "+" 号，选择第3项”Module Dependency"，然后勾选"OpenCVLibrary420"，点击"OK"即可。

2.4. 修改app的"build.grade"文件

修改的内容主要是CMake的一些编译参数、C++的风格和要编译生成的ARM平台的SO库。修改后的内容可参考如下：

apply plugin: 'com.android.application'android {    compileSdkVersion 29    buildToolsVersion "29.0.2"    defaultConfig {        applicationId "com.example.facedetection"        minSdkVersion 15        targetSdkVersion 29        versionCode 1        versionName "1.0"        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"        externalNativeBuild {            cmake {                arguments "-DANDROID_ARM_NEON=TRUE","-DCMAKE_BUILD_TYPE=Release","-DANDROID_TOOLCHAIN=clang"                cppFlags "-std=c++14 -frtti -fexceptions -ljnigraphics"            }            // ndk编译生成so库            ndk{                abiFilters 'x86','x86_64','armeabi-v7a','arm64-v8a'            }        }    }    buildTypes {        release {            minifyEnabled false            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'        }    }    externalNativeBuild {        cmake {            path "CMakeLists.txt"            version "3.10.2"        }    }    //包含头文件    sourceSets {        main{            jniLibs.srcDirs = ['src/main/cpp/libs/opencv2']        }    }}dependencies {    implementation fileTree(dir: 'libs', include: ['*.jar'])    implementation 'androidx.appcompat:appcompat:1.1.0'    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'    testImplementation 'junit:junit:4.12'    androidTestImplementation 'androidx.test:runner:1.2.0'    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'    implementation project(path: ':OpenCVLibrary420')}

2.5. 修改"CMakeLists.txt"

这里修改的参数较多，直接附上我的"CMakeLists.txt"内容。

# 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.# 指定cmake的最小版本，确保能使用某些新特性构建项目cmake_minimum_required(VERSION 3.4.1)# 输出详细信息set(CMAKE_VERBOSE_MAKEFILE on)# 支持-std=gnu++14set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++14")# 包含头文件目录include_directories(src/main/cpp/include)# 设置库目录set(LIBRARY_DIRS "${CMAKE_SOURCE_DIR}/src/main/cpp/libs/opencv2")# 添加opencv动态库add_library(libopencv_java4 SHARED IMPORTED)   #动态加载方式# 指定库路径set_target_properties( # Specifies the target library.        libopencv_java4        # Specifies the parameter you want to define.        PROPERTIES IMPORTED_LOCATION        # Provides the path to the library you want to import.        "${LIBRARY_DIRS}/${ANDROID_ABI}/libopencv_java4.so" )# 设置dlib目录# 如果使用下面的就是用的dlib的cmake文件，编译会比较慢，如果要使用可取消下行注释# include(src/main/cpp/include/dlib/cmake)# 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.        face-lib        # Sets the library as a shared library.        SHARED        # Provides a relative path to your source file(s).        # 这里可能需要加载多个文件，将文件依次填写在下面即可        ${SRC_LIST}        src/main/cpp/source/face-lib.cpp        )# 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.        face-lib        #dlib        jnigraphics        libopencv_java4        # Links the target library to the log library        # included in the NDK.        ${log-lib})# 指定release编译选项# 下面方法有时可能会有些问题，就是不能指定编译Release版本，后面有时间再解决这个问题# set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -s -O3 -Wall")# set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -s -O3 -Wall")

至此，Androd + C/CPP + OpenCV/Dlib的整个开发环境已经搭建完成，并能使用Cmake 生成支持ARM平台的C++ SO库。如果有什么问题，可以添加QQ:396793304，或加QQ群:210250364一起交流讨论。

Android+OpenCV4开发(一)——Android(安卓)NDK开发环境配置（生成C++ SO库）

目录

前言：