[Development] Android NDK Android.mk configure dynamic library (Android Studio configuration dynamic library | dynamic libraries to load the version restriction | chapter for reference only recommend using CMake configuration DLL)

Article Directory

I. Android Studio Android.mk used to configure dynamic library summary
II. Third-party sources of dynamic libraries
III. Configuring Android.mk build script path
IV. Precompiled third-party dynamic libraries (Android.mk)
V. Dynamic link library (DLL set dependent)
VI. Java native methods and custom code to load dynamic library
VII. C code to call the DLL function
VIII. Dynamic libraries to load the version limit (6.0 Android.mk can not be used to configure dynamic libraries)
IX. Complete code sample

1. Build.gradle Configuration Example
2. Android.mk Configuration Example
3. Java code sample
4. C code sample
5 operating results. (Android 4.3 phone | 6.0 system can not run)

X. Blog resources

I. Android Studio Android.mk used to configure dynamic library summary

Android Studio Android.mk used to configure third-party dynamic libraries:

① Android.mk script path settings: Configuration Module Android.mk in build script build.gradle level path to the script;

    externalNativeBuild {
        ndkBuild{
            path "src/main/ndkBuild_Shared/Android.mk"
        }
    }

② precompiled third-party dynamic libraries: in Android.mk precompiled dynamic library, pay attention to the dynamic library static library to use a different configuration, where a dynamic library, for example:

include $(CLEAR_VARS)
LOCAL_MODULE := add
LOCAL_SRC_FILES := libadd.so
include $(PREBUILT_SHARED_LIBRARY)

③ dynamic link library: pre Android.mk link in static library or dynamic link library, the dynamic attention database static configuration different libraries used, for example where a dynamic library:

LOCAL_SHARED_LIBRARIES := add

④ Java code implementation: declare native methods to load the compiled dynamic library;

⑤ C code implementation: function declaration in the library, call the function in a dynamic library;

II. Third-party sources of dynamic libraries

1. third-party dynamic libraries Source: add.c;

#include <stdio.h>

int add(int a, int b){
	return a + b;
}

. 2 Ubuntu cross-compilation process: Reference [Ubuntu] Android NDK development of cross-compiled libraries (Android library dynamic cross compiler | Android static library cross-compiler) , and finally compile libadd.so dynamic libraries, and libadd.a static library;

III. Configuring Android.mk build script path

1 source compiler / packaged configuration principle: [development] Android NDK Android Studio NDK's configuration (source compiler configuration | build script configuration | packaged configuration | CMake configuration | ndkBuild configuration):. I compiler source code configuration

2. build script path configuration principle: [development] Android NDK Android Studio NDK's configuration (source compiler configuration | build script configuration | packaged configuration | CMake configuration | ndkBuild configuration): II build script configuration.

3. Here Android.mk disposed directly build script path: to omit nothing configuration, leaving only the configuration NDK;

apply plugin: 'com.android.application'

android {
    ...
    defaultConfig {
     	...
        // 配置 AS 工程中的 C/C++ 源文件的编译
        //     defaultConfig 内部的 externalNativeBuild 配置的是配置 AS 工程的 C/C++ 源文件编译参数
        //     defaultConfig 外部的 externalNativeBuild 配置的是 CMakeList.txt 或 Android1.mk 构建脚本的路径
        externalNativeBuild {
            /*cmake {
                cppFlags ""

                //配置编译 C/C++ 源文件为哪几个 CPU 指令集的函数库 (arm , x86 等)
                abiFilters "armeabi-v7a"
            }*/
            ndkBuild{
                abiFilters "armeabi-v7a" /*, "arm64-v8a", "x86", "x86_64"*/
            }
        }

        //配置 APK 打包 哪些动态库
        //  示例 : 如在工程中集成了第三方库 , 其提供了 arm, x86, mips 等指令集的动态库
        //        那么为了控制打包后的应用大小, 可以选择性打包一些库 , 此处就是进行该配置
        ndk{
            // 打包生成的 APK 文件指挥包含 ARM 指令集的动态库
            abiFilters "armeabi-v7a" /*, "arm64-v8a", "x86", "x86_64"*/
        }

    }

    // 配置 NDK 的编译脚本路径
    // 编译脚本有两种 ① CMakeList.txt ② Android1.mk
    //     defaultConfig 内部的 externalNativeBuild 配置的是配置 AS 工程的 C/C++ 源文件编译参数
    //     defaultConfig 外部的 externalNativeBuild 配置的是 CMakeList.txt 或 Android1.mk 构建脚本的路径
    externalNativeBuild {

        // 配置 CMake 构建脚本 CMakeLists.txt 脚本路径
        /*cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }*/

        // 配置 Android1.mk 构建脚本路径
        ndkBuild{
            path "src/main/ndkBuild_Shared/Android.mk"
            //path "src/main/ndkBuild_Static/Android.mk"
        }
    }
 	...
}
...

IV. Precompiled third-party dynamic libraries (Android.mk)

1. Clear variables: (begin the Add module configuration)

① Role: To configure the new module must first remove LOCAL_XXX variable;

② exceptions: One exception is not cleared LOCAL_PATH variable;

③ identification module begins: the include $ (CLEAR_VARS), mark the beginning of a general configuration of a module;

④ end module: the include $ (XXX_STATIC_LIBRARY) / the include $ (XXX_SHARED_LIBRARY) typically arranged as a module end flag;

include $(CLEAR_VARS)

2. Configure dynamic library name:

① automatic generation of library Name premise: no LOCAL_MODULE_FILENAME configuration, it will automatically generate a library name;

② dynamic library naming conventions: the LOCAL_MODULE name basis, add lib prefix (if no longer add the prefix in front of lib) and .so suffix;

③ a dynamic library name: libadd.so;

LOCAL_MODULE := add

3 Set precompiled dynamic library path:

LOCAL_SRC_FILES := libadd.so

4. Set precompiled dynamic library: (end of the Add Module Configuration)

include $(PREBUILT_SHARED_LIBRARY)

5. Complete third-party dynamic libraries pre-compiled module configuration:

Here Insert Picture Description

# II . 预编译第三方动态库


# 1 . 清除变量 ( add 模块配置开始 )
#	① 作用 : 配置新的模块之前都要先清除 LOCAL_XXX 变量
#	② 例外情况 : 但是不会清除 LOCAL_PATH 变量
#	③ 模块开始 : include $(CLEAR_VARS)
#  	④ 模块结尾 : include $(XXX_STATIC_LIBRARY) / include $(XXX_SHARED_LIBRARY)
include $(CLEAR_VARS)

# 2 . 配置动态库名称
#	① 自动生成函数库名称前提 : 没有 LOCAL_MODULE_FILENAME 配置 , 就会自动生成函数库名称
# 	② 动态库命名规则 : 在 LOCAL_MODULE 名称基础上 , 添加 lib 前缀和 .so 后缀
# 	③ 生成动态库名称 : libadd.so
LOCAL_MODULE := add

# 3 . 预编译的动态库路径
LOCAL_SRC_FILES := libadd.so

# 4 . 设置预编译动态库 ( add 模块配置结束 )
include $(PREBUILT_SHARED_LIBRARY)

V. Dynamic link library (DLL set dependent)

Set the dynamic library dependencies:

① dependencies: compile native-lib module, you need to add a static link library;

② add dynamic libraries: the Add module is a pre-compiled libraries, precompiled third-party content is dynamic libraries introduced;

LOCAL_SHARED_LIBRARIES := add

Here Insert Picture Description

# IV . 配置动态库模块


# 1 . 清除变量 ( native-lib 模块配置开始 )
#	① 作用 : 配置新的模块之前都要先清除 LOCAL_XXX 变量
#	② 例外情况 : 但是不会清除 LOCAL_PATH 变量
include $(CLEAR_VARS)


# 2 . 配置动态库名称
#	① 自动生成函数库名称前提 : 没有 LOCAL_MODULE_FILENAME 配置 , 就会自动生成函数库名称
# 	② 动态库命名规则 : 在 LOCAL_MODULE 名称基础上 , 添加 lib 前缀 和 .so 后缀
# 	③ 生成动态库名称 : libnative-lib.so
LOCAL_MODULE := native-lib


# 3 . 编译的源文件
LOCAL_SRC_FILES := native-lib.c

# 4 . 设置动态依赖库
#	① 依赖库 : 编译 native-lib 模块 , 需要链接 add 动态库
#	② add 动态库 : add 模块是一个预编译库 , 预编译内容是引入的第三方动态库
LOCAL_SHARED_LIBRARIES := add

# 5 . 链接日志库
LOCAL_LDLIBS := -llog

# 6 . 设置预编译动态库 ( native-lib 模块配置结束 )
include $(BUILD_SHARED_LIBRARY)

VI. Java native methods and custom code to load dynamic library

1. Declare and use native methods:

public native String stringFromJNI();

2. load dynamic library: here the two dynamic libraries to load;

        System.loadLibrary("add");
        System.loadLibrary("native-lib");

Here Insert Picture Description

VII. C code to call the DLL function

1. Declare external dynamic library method:

//声明 libadd.so 动态库中的方法
extern int add(int a, int b);

2 DLL calls the method:

//调用动态库中的函数
int sum = add(1, 2);

Here Insert Picture Description

VIII. Dynamic libraries to load the version limit (6.0 Android.mk can not be used to configure dynamic libraries)

1. Problem Description:

6.0 release, the use of third-party Android.mk build scripts precompiled dynamic library, if used in the program System.loadLibrary load the precompiled libraries will error;

6.0 The following mobile versions (not including the 6.0 version), System.loadLibrary need to manually load-dependent dynamic library;

Mobile version 6.0 and above, System.loadLibrary will automatically load-dependent dynamic libraries can not be loaded at this time dependent dynamic library, or an error occurs;

2 error message: more than 6.0 Android.mk phone can not be used to load dynamic library, once loaded collapse; reported the following error;

2020-02-13 01:58:38.044 23033-23033/kim.hsl.mk E/AndroidRuntime: FATAL EXCEPTION: main
    Process: kim.hsl.mk, PID: 23033
    java.lang.UnsatisfiedLinkError: dlopen failed: library "Y:/002_WorkSpace/001_AS/006_NDK_Android_mk/app/build/intermediates/ndkBuild/debug/obj/local/armeabi-v7a/libadd.so" not found
        at java.lang.Runtime.loadLibrary0(Runtime.java:977)
        at java.lang.System.loadLibrary(System.java:1567)
        at kim.hsl.mk.MainActivity.<clinit>(MainActivity.java:19)
        ...

3 solutions: more than 6.0 phones can only be used to configure CMake dynamic library, or use the static library;

. 4 CMake configuration scheme reference: [] NDK Android NDK development of cross-compiler (Ubuntu in cross-compile a dynamic library | Android Studio is configured to use a third-party DLL)

IX. Complete code sample

1. Build.gradle Configuration Example

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.0"
    defaultConfig {
        applicationId "kim.hsl.mk"
        minSdkVersion 15
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

        // 配置 AS 工程中的 C/C++ 源文件的编译
        //     defaultConfig 内部的 externalNativeBuild 配置的是配置 AS 工程的 C/C++ 源文件编译参数
        //     defaultConfig 外部的 externalNativeBuild 配置的是 CMakeList.txt 或 Android1.mk 构建脚本的路径
        externalNativeBuild {
            /*cmake {
                cppFlags ""

                //配置编译 C/C++ 源文件为哪几个 CPU 指令集的函数库 (arm , x86 等)
                abiFilters "armeabi-v7a"
            }*/
            ndkBuild{
                abiFilters "armeabi-v7a" /*, "arm64-v8a", "x86", "x86_64"*/
            }
        }

        //配置 APK 打包 哪些动态库
        //  示例 : 如在工程中集成了第三方库 , 其提供了 arm, x86, mips 等指令集的动态库
        //        那么为了控制打包后的应用大小, 可以选择性打包一些库 , 此处就是进行该配置
        ndk{
            // 打包生成的 APK 文件指挥包含 ARM 指令集的动态库
            abiFilters "armeabi-v7a" /*, "arm64-v8a", "x86", "x86_64"*/
        }

    }

    // 配置 NDK 的编译脚本路径
    // 编译脚本有两种 ① CMakeList.txt ② Android1.mk
    //     defaultConfig 内部的 externalNativeBuild 配置的是配置 AS 工程的 C/C++ 源文件编译参数
    //     defaultConfig 外部的 externalNativeBuild 配置的是 CMakeList.txt 或 Android1.mk 构建脚本的路径
    externalNativeBuild {

        // 配置 CMake 构建脚本 CMakeLists.txt 脚本路径
        /*cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }*/

        // 配置 Android1.mk 构建脚本路径
        ndkBuild{
            path "src/main/ndkBuild_Shared/Android.mk"
            //path "src/main/ndkBuild_Static/Android.mk"
        }
    }

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

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'
}

2. Android.mk Configuration Example

# I . 保存构建脚本的路径 , 并赋值给 LOCAL_PATH 变量


#   ① 内置函数 : my-dir 是 NDK 内置的函数 , 获取当前的目录路径
#	在该案例中就是 Android.mk 文件所在的目录的绝对路径 , 工程根目录/app/src/main/cpp
#	将该目录赋值给 LOCAL_PATH 变量
#	所有的 Android1.mk 的第一行配置都是该语句

LOCAL_PATH := $(call my-dir)



# II . 预编译第三方动态库


# 1 . 清除变量 ( add 模块配置开始 )
#	① 作用 : 配置新的模块之前都要先清除 LOCAL_XXX 变量
#	② 例外情况 : 但是不会清除 LOCAL_PATH 变量
#	③ 模块开始 : include $(CLEAR_VARS)
#  	④ 模块结尾 : include $(XXX_STATIC_LIBRARY) / include $(XXX_SHARED_LIBRARY)
include $(CLEAR_VARS)

# 2 . 配置动态库名称
#	① 自动生成函数库名称前提 : 没有 LOCAL_MODULE_FILENAME 配置 , 就会自动生成函数库名称
# 	② 动态库命名规则 : 在 LOCAL_MODULE 名称基础上 , 添加 lib 前缀 和 .so 后缀
# 	③ 生成动态库名称 : libadd.so
LOCAL_MODULE := add

# 3 . 预编译的动态库路径
LOCAL_SRC_FILES := libadd.so

# 4 . 设置预编译动态库 ( add 模块配置结束 )
include $(PREBUILT_SHARED_LIBRARY)



# III . 打印变量值


# 打印 LOCAL_PATH 值
# Build 打印内容 : LOCAL_PATH : Y:/002_WorkSpace/001_AS/005_NDK_Compile/app/src/main/cpp
# 编译 APK 时会在 Build 中打印
$(info LOCAL_PATH : $(LOCAL_PATH))



# IV . 配置动态库模块


# 1 . 清除变量 ( native-lib 模块配置开始 )
#	① 作用 : 配置新的模块之前都要先清除 LOCAL_XXX 变量
#	② 例外情况 : 但是不会清除 LOCAL_PATH 变量
include $(CLEAR_VARS)


# 2 . 配置动态库名称
#	① 自动生成函数库名称前提 : 没有 LOCAL_MODULE_FILENAME 配置 , 就会自动生成函数库名称
# 	② 动态库命名规则 : 在 LOCAL_MODULE 名称基础上 , 添加 lib 前缀 和 .so 后缀
# 	③ 生成动态库名称 : libnative-lib.so
LOCAL_MODULE := native-lib


# 3 . 编译的源文件
LOCAL_SRC_FILES := native-lib.c

# 4 . 设置静态依赖库
#	① 依赖库 : 编译 native-lib 模块 , 需要链接 add 静态库
#	② add 静态库 : add 模块是一个预编译库 , 预编译内容是引入的第三方动态库
LOCAL_SHARED_LIBRARIES := add

# 5 . 链接日志库
LOCAL_LDLIBS := -llog

# 6 . 设置预编译动态库 ( native-lib 模块配置结束 )
include $(BUILD_SHARED_LIBRARY)



# V . 配置动态库与静态库区别


#	1 . 预编译时的路径不一致 :
#		① 动态库路径 : libadd.so
#		② 静态库路径 : libadd.a

#	2 . 预编译时结束配置不一致 :
#		① 动态库配置 : include $(PREBUILT_SHARED_LIBRARY)
#		② 静态库配置 : include $(PREBUILT_STATIC_LIBRARY)

#	3 . 链接依赖库时配置不一致 :
#		① 动态库依赖配置 : LOCAL_SHARED_LIBRARIES
#		② 静态库依赖配置 : LOCAL_STATIC_LIBRARIES

3. Java code sample

package kim.hsl.mk;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    static {

        // 1 . 加载动态库的情况 : ( 必须不能注释下面的代码 )
        //      ① 6.0 以下的版本 : 需要手动加载依赖库 libadd.so
        //      ② 6.0 以上的版本 : 无法使用 Android.mk 构建脚本加载第三方动态库
        //                         此情况下, 无论是否手动加载 libadd.so 都会报错
        //
        // 2 . 加载静态库的情况 : ( 必须注释掉下面的这行代码 )
        System.loadLibrary("add");

        System.loadLibrary("native-lib");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tv = findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());
    }

    public native String stringFromJNI();
}

4. C code sample

#include <jni.h>

#include <stdio.h>
#include <stdlib.h>

#include <android/log.h>


//调用 libadd.so 动态库中的方法
extern int add(int a, int b);

JNIEXPORT jstring JNICALL
Java_kim_hsl_mk_MainActivity_stringFromJNI(
        JNIEnv *env,
        jobject obj) {

    //调用动态库中的函数
    int sum = add(1, 2);

    // Logcat 打印计算结果
    __android_log_print(ANDROID_LOG_INFO, "JNI_TAG", "Native Caculate : %d + %d = %d", 1, 2, sum);

    //将加法运算转为字符串
    char str[50] = "0";
    //字符串格式化
    sprintf(str, "Native Caculate : Static Library : %d + %d = %d", 1, 2, sum);

    return (*env)->NewStringUTF(env, str);
}