JNI开发基础系列--链接第三方动态库

链接第三方动态库

下面模拟链接第三方动态库的过程
一、编译一个动态库
1.1 在CMakeLists.txt中配置(其实也是androidStudio新建一个包含c++的默认配置)

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/add.c )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( # Specifies the target library.                       native-lib                       # Links the target library to the log library                       # included in the NDK.                       ${log-lib} )

1.2 在add.c中添加一个测试方法

#define TAG "399"#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,TAG,__VA_ARGS__)int add(int a, int b){    LOGE("c开始计算");    return a+b;}

1.3 点击Rebuild Project,等待编译结束，切到到project项目下的app/intermediates/cmake/debug/obj，如下图：

把所有平台的so库复制下来添加到测试工程的lib目录下，再在app的bulid.gradle的android节点下添加：

    sourceSets.main {        jniLibs.srcDirs = ['libs']        jni.srcDirs = []    }

到这里需要模拟依赖的第三方库就做好了，如果有这直接copy到lib中，可以跳过此步骤，直接看第二步

二、配置CMakeLists.txt，链接到这个第三方库
在CMakeLists.txt中添加和修改

#需添加#设置so库路径,设置my_lib_path为相对CMakeLists.txt路径下的libs目录set(my_lib_path ${CMAKE_SOURCE_DIR}/libs)#将第三方库作为动态库引用，native-lib其实就是刚刚编译的so库，全名为libnative-lib.soadd_library( native-lib             SHARED             IMPORTED )#需添加#指名第三方库的绝对路径ANDROID_ABI为build.gradle中配置要编译的平台set_target_properties( native-lib                       PROPERTIES IMPORTED_LOCATION                       ${my_lib_path}/${ANDROID_ABI}/libnative-lib.so )#需修改                   #链接动态库                      target_link_libraries( # Specifies the target library.                       filelib//自己开发用的                       native-lib//第三方动态库                       # Links the target library to the log library                       # included in the NDK.                       ${log-lib} )#filelib为自己需要编译的.so库名字add_library( # Sets the name of the library.             filelib             # Sets the library as a shared library.             SHARED             # Provides a relative path to your source file(s).             src/main/cpp/hello.c )#不修改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 )

三、开始写自己的代码测试
3.1 新建头文件add.h 如下：声明add方法：

#ifndef NDKTEST2_ADD_H#define NDKTEST2_ADD_Hextern int add(int a,int b);#endif //NDKTEST2_ADD_H

3.2
java中编写native 方法

 public native int add(int a,int b);

c中调用第三方库

JNIEXPORT jint JNICALL Java_com_cool_ndktest2_MainActivity_add        (JNIEnv * env, jobject jobj,jint jint1,jint jint2){        int result = add(jint1,jint2);    return result;}

3.3 java中使用
3.3.1 加载动态库

    static {        System.loadLibrary("native-lib");        System.loadLibrary("filelib");    }

3.3.2 java调用及运行结果

java调用：int sum = add(100,100);Log.e("399","sum: " + sum);运行结果：E/399: c中开始计算E/399: sum: 200