Android Studio的native jni so编译配置

柔情只为你懂 2022-05-22 01:45 237阅读 0赞

在Android Studio中编译jni和so库，可以使用app/CMakeList.txt,也可以使用Android.mk

# AndroidStudio 进行 JNI / NDK 开发：初步配置及使用 #

2017年09月08日 12:03:44

阅读数：5118

**说干就干！**

**JNI**：Java Native Interface（Java 本地编程接口），**一套编程规范**，它提供了若干的 API 实现了 Java 和其他语言的通信（主要是 C/C++）。Java 可以通过 JNI 调用本地的 C/C++ 代码，本地的 C/C++ 代码也可以调用 java 代码。Java 通过 C/C++ 使用本地的代码的一个关键性原因在于 C/C++ 代码的高效性。

**NDK**：Native Development Kit（本地开发工具），**一系列工具的集合**，提供了一系列的工具，帮助开发者快速开发 C/C++，极大地减轻了开发人员的打包工作。

### 一、安装所需工具 ###

![SouthEast][]

*  NDK：这套工具集允许为 Android 使用 C 和 C++ 代码。
 *  CMake：一款外部构建工具，可与 Gradle 搭配使用来构建原生库。如果只计划使用 ndk-build，则不需要此组件。
 *  LLDB：一种调试程序，Android Studio 使用它来调试原生代码。

> Ps：CMake 是 AS 2.2 之后加入的一个跨平台的安装（编译）工具，可以用简单的语句来描述所有平台的安装(编译过程)，简单来说就是简化 JNI 开发的编译步骤，不用像以前那样要各种手动生成（[http://www.jianshu.com/p/e7c2c63fa70e][http_www.jianshu.com_p_e7c2c63fa70e]）

### 二、创建支持 C/C++ 的新项目 ###

**1、新建支持 C/C++ 的新项目**

只要在新建项目时勾上这里就行：

![SouthEast 1][]

在向导的 Customize C++ Support 部分，有下列自定义项目可供选择：

>  *  C++ Standard：使用下拉列表选择使用哪种 C++ 标准。选择 Toolchain Default 会使用默认的 CMake 设置。
>  *  Exceptions Support：如果希望启用对 C++ 异常处理的支持，请选中此复选框。如果启用此复选框，Android Studio 会将 -fexceptions 标志添加到模块级 build.gradle文件的 cppFlags中，Gradle 会将其传递到 CMake。
>  *  Runtime Type Information Support：如果希望支持 RTTI，请选中此复选框。如果启用此复选框，Android Studio 会将 -frtti 标志添加到模块级 build.gradle文件的 cppFlags中，Gradle 会将其传递到 CMake。

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**2、主要项目结构**

对于开发者来说，主要关注这两个地方：

![SouthEast 3][]

*  **cpp 文件夹：用于编写 C/C++代码**
 *  **CMakeLists.txt：CMake 脚本配置文件**

**3、编写代码安装运行**

新建支持 C/C++ 的新项目时有默认的实例代码：

public class MainActivity extends AppCompatActivity {
    
        // Used to load the 'native-lib' library on application startup.
        // 加载本地库
        static {
            System.loadLibrary("native-lib");
        }
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            // Example of a call to a native method
            TextView tv = (TextView) findViewById(R.id.sample_text);
            tv.setText(stringFromJNI());
        }
    
        /**
         * A native method that is implemented by the 'native-lib' native library,
         * which is packaged with this application.
         */
        // 本地方法
        public native String stringFromJNI();
    }

#include <jni.h>
    #include <string>
    
    extern "C"
    JNIEXPORT jstring
    
    JNICALL
    Java_com_xq_jnidemo01_MainActivity_stringFromJNI(JNIEnv *env,jobject /* this */) {
        std::string hello = "Hello from C++";
        return env->NewStringUTF(hello.c_str());
    }

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### 三、在原有旧项目中引入 ###

**1、新建 C/C++ 源码文件夹和文件**

![SouthEast 5][]

**2、编写 CMakeLists.txt 文件**

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> **Ps：**如果嫌编写 CMakeLists.txt 文件麻烦，就直接新建一个支持 C/C++ 的新项目，拷贝修改即可（拷贝之后可以删去文件中的注释，便于阅读）

![SouthEast 7][]

# TODO 设置构建本机库文件所需的 CMake的最小版本
    cmake_minimum_required(VERSION 3.4.1)
    
    # TODO 添加自己写的 C/C++源文件
    add_library( demo-lib
                 SHARED
                 src/main/cpp/demo-lib.cpp )
    
    # TODO 依赖 NDK中的库
    find_library( log-lib
                  log )
    
    # TODO 将目标库与 NDK中的库进行连接
    target_link_libraries( demo-lib
                           ${log-lib} )

**3、配置 build.gradle 文件**

![这里写图片描述][SouthEast 8]

android {
        ...
        defaultConfig {
            ...
            externalNativeBuild {
                cmake {
                    // 默认是 “ cppFlags "" ”
                    // 如果要修改 Customize C++ Support 部分，可在这里加入
                    cppFlags "-frtti -fexceptions"
                }
            }
        }
        buildTypes {
            ...
        }
        externalNativeBuild {
            cmake {
                path "CMakeLists.txt"
            }
        }
    }
    
    dependencies {
        ...
    }

**最后是编写代码安装运行 …**

### 四、几个要注意的点 ###

**1、要在哪个类运用 JNI ，就得加载相应的动态库**

// 加载动态库
        static {
            System.loadLibrary("demo-lib");
        }

*  1
 *  2
 *  3
 *  4

**2、快速生成代码：Alt + Enter**

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**3、新建 C/C++ 源代码文件，要添加到 CMakeLists.txt 文件中**

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![SouthEast 11][]

**4、引入第三方 .so文件，要添加到 CMakeLists.txt 文件中**

（1）新建资源文件夹 jniLibs（貌似在 libs中也行，只要在 CMakeLists.txt中添加路径指示）

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（2）在 CMakeLists.txt中添加路径指示

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> Ps：这里要注意两个地方
> 
> **① 在定义库的名字时，不要加前缀 lib 和后缀 .so，不然会报错：java.lang.UnsatisfiedLinkError: Couldn’t load xxx : findLibrary**【findLibrary returned null错误： [http://blog.csdn.net/treasure3334/article/details/17170927][http_blog.csdn.net_treasure3334_article_details_17170927]】  
> **② ABI 文件夹上面不要再分层，直接用“jniLibs/$\{ANDROID\_ABI\}/”的格式，不然也会报错**

# TODO 添加第三方库
    # TODO add_library(libavcodec-57
    # TODO 原先生成的.so文件在编译后会自动添加上前缀lib和后缀.so，
    # TODO       在定义库的名字时，不要加前缀lib和后缀 .so，
    # TODO       不然会报错:java.lang.UnsatisfiedLinkError: Couldn't load xxx : findLibrary returned null
    add_library(avcodec-57
                # TODO STATIC表示静态的.a的库，SHARED表示.so的库
                SHARED
                IMPORTED)
    set_target_properties(avcodec-57
                          PROPERTIES IMPORTED_LOCATION
                          # TODO ${CMAKE_SOURCE_DIR}：表示 CMakeLists.txt的当前文件夹路径
                          # TODO ${ANDROID_ABI}：编译时会自动根据 CPU架构去选择相应的库
                          # TODO ABI文件夹上面不要再分层，直接就 jniLibs/${ANDROID_ABI}/
                          # TODO ${CMAKE_SOURCE_DIR}/src/main/jniLibs/ffmpeg/${ANDROID_ABI}/libavcodec-57.so
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libavcodec-57.so)
    add_library(avdevice-57
                SHARED
                IMPORTED)
    set_target_properties(avdevice-57
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libavdevice-57.so)

（3）将自己编写的 C/C++源文件与第三方库进行连接

![SouthEast 14][]

**5、引入第三方 .h 文件夹，要添加到 CMakeLists.txt 文件中**

![SouthEast 15][]

> **Ps：**本来想在 jniLibs 中引入，但编译会出错，所以只能在 CPP 资源文件夹中引入

# TODO include_directories( src/main/jniLibs/${ANDROID_ABI}/include )
    # TODO 路径指向上面会编译出错，指向下面的路径就没问题
    include_directories( src/main/cpp/ffmpeg/include )

*  1
 *  2
 *  3

![SouthEast 16][]

**6、CPP 资源文件夹中的同名问题**

CPP 资源文件夹下面的文件和文件夹不能重名，不然 System.loadLibrary() 时找不到，会报错：java.lang.UnsatisfiedLinkError: Native method not found

![SouthEast 17][]

**7、undefined reference to ‘xxx’**

// 使C与C++能够正常混编
    // 指示编译器按照C语言进行编译
    extern "C"
    {
        ...
    }

![SouthEast 18][]

**8、error: ‘xxx.so’，needed by ‘xxxx.so’，missing and no known rule to make it**

不同厂商的 Android 手机支持的 CPU 架构不同【Android-ABIFilter：[http://blog.csdn.net/qq\_32452623/article/details/71076023][http_blog.csdn.net_qq_32452623_article_details_71076023]】，一般引入的第三方 .so 文件有多个 ABI 的类型，Cmake会默认对下面 7 个ABI分别调试，但如果只引入一部分，那么要在 build.gradle 中设置 ndk 的 abiFilters 属性：

externalNativeBuild {
                cmake {
                    // 默认是 “ cppFlags "" ”
                    // 如果要修改 Customize C++ Support 部分，可在这里加入
                    cppFlags "-frtti -fexceptions"
                }
            }
            ndk {
                // abiFiliter： ABI 过滤器（application binary interface，应用二进制接口）
                // Android 支持的 CPU 架构
                abiFilters 'armeabi'//,'armeabi-v7a','arm64-v8a','x86','x86_64','mips','mips64'
            }

![SouthEast 19][]

本人示例：

![70][]

![70 1][]

CMakeList.txt:

# 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 3.4.1)
    
    # 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.
                 native-lib
    
                 # Sets the library as a shared library.
                 SHARED
    
                 # Provides a relative path to your source file(s).
                 src/main/cpp/native-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.
                           native-lib
    
                           # Links the target library to the log library
                           # included in the NDK.
                           ${log-lib} )
    
    
    add_library(
                 sffdecoder
                 SHARED
                 src/main/cpp/simplest_ffmpeg_decoder.c )
    
    
    add_library(
                 avcodec-56
                 SHARED
                 IMPORTED )
    set_target_properties(avcodec-56
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libavcodec-56.so)
    
    
    add_library(
                 avdevice-56
                 SHARED
                 IMPORTED )
    set_target_properties(avdevice-56
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libavdevice-56.so)
    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 )
    #target_link_libraries(
    #                       avdevice-56
    #                       ${log-lib} )
    
    add_library(
                 avfilter-5
                 SHARED
                 IMPORTED )
    set_target_properties(avfilter-5
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libavfilter-5.so)
    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 )
    #target_link_libraries(
     #                      avfilter-5
     #                      ${log-lib} )
    
    add_library(
                 avformat-56
                 SHARED
                 IMPORTED )
    set_target_properties(avformat-56
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libavformat-56.so)
    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 )
    #target_link_libraries(
    #                       avformat-56
     #                      ${log-lib} )
    
    add_library(
                 avutil-54
                 SHARED
                 IMPORTED )
    set_target_properties(avutil-54
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libavutil-54.so)
    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 )
    #target_link_libraries(
    #                       avutil-54
     #                      ${log-lib} )
    
    add_library(
                 postproc-53
                 SHARED
                 IMPORTED )
    set_target_properties(postproc-53
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libpostproc-53.so)
    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 )
    #target_link_libraries(
    #                       postproc-53
    #                       ${log-lib} )
    
    
    
    
    
    
    
    add_library(
                 swresample-1
                 SHARED
                 IMPORTED )
    set_target_properties(swresample-1
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libswresample-1.so)
    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 )
    #target_link_libraries(
    #                       swresample-1
    #                       ${log-lib} )
    
    
    
    add_library(
                 swscale-3
                 SHARED
                 IMPORTED )
    set_target_properties(swscale-3
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libswscale-3.so)
    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 )
    #target_link_libraries(
     #                      swscale-3
     #                      ${log-lib} )
    
    target_link_libraries(sffdecoder
    avcodec-56
    avdevice-56
    avfilter-5
    avformat-56
    avutil-54
    postproc-53
    swresample-1
    swscale-3
    ${log-lib} )
    
    include_directories( src/main/cpp/include )

app/build.gradle

apply plugin: 'com.android.application'
    
    android {
        compileSdkVersion 26
        defaultConfig {
            applicationId "com.example.champion.ffmpeghelloworld"
            minSdkVersion 24
            targetSdkVersion 26
            versionCode 1
            versionName "1.0"
            testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
            externalNativeBuild {
                cmake {
                    cppFlags ""
                }
            }
            ndk {
                // abiFiliter： ABI 过滤器（application binary interface，应用二进制接口）
                // Android 支持的 CPU 架构
                abiFilters 'armeabi'//,'armeabi-v7a','arm64-v8a','x86','x86_64','mips','mips64'
            }
        }
        buildTypes {
            release {
                minifyEnabled false
                proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            }
        }
        externalNativeBuild {
            cmake {
                path "CMakeLists.txt"
            }
        }
    
        sourceSets { main { jni.srcDirs = ['src/main/jni', 'src/main/jni/'] } }
    }
    
    dependencies {
        implementation fileTree(dir: 'libs', include: ['*.jar'])
        implementation 'com.android.support.constraint:constraint-layout:1.1.0'
        testImplementation 'junit:junit:4.12'
        androidTestImplementation 'com.android.support.test:runner:1.0.2'
        androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    }

[SouthEast]: /images/20220522/ff3b30d43ec64518a59d1a88e35c466b.png
[http_www.jianshu.com_p_e7c2c63fa70e]: http://www.jianshu.com/p/e7c2c63fa70e
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[http_blog.csdn.net_treasure3334_article_details_17170927]: http://blog.csdn.net/treasure3334/article/details/17170927
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[http_blog.csdn.net_qq_32452623_article_details_71076023]: http://blog.csdn.net/qq_32452623/article/details/71076023
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