一、JNI规范so库调用

在 Android Studio生成自己的so库中已经创建了自己的so库，这是一个JNI规范的so库，可以直接将so库放到libs中，并按照上面文章中MainActivity中的调用方法使用。

1、build.gradle（app）配置

android {

    defaultConfig {
        // 加载so类型
        ndk {
            abiFilters 'armeabi-v7a', 'arm64-v8a', 'x86', 'x86_64'
        }
    }
    // so库路径
    sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
    }
}

2、加载so库中方法

public class NativeImpl {
    // 加载so库
    static {
        System.loadLibrary("native_xiaoxu");
    }

    /**
     * 添加 native 方法
     */
    public static native String getUserName();
}

在Sudio中方法名虽然显示红色，但不影响使用。

3、Activity中调用方法

NativeImpl.getUserName();

二、非JNI规范的so库调用

在 Android Studio生成自己的so库中如果我们没有使用 native-lib.cpp 对命名进行规范化，我们如何直接调用 cpp 中的方法？这时，这时我们需要创建一个自己的so库，在自己的so库中调用三方so库，再在自己的程序中调用自己的so库。

我们还是在之前项目的基础上进行修改，并使用之前生成的so库。

1、放入so库

gradle 4.0开始就对jni的预编译依赖引用方式做出了修改，原来的直接放在“src/main/jniLibs”中的方法已经作废了，所以要把jniLibs里的预编译库换个位置，比如把jniLibs改为mylibs，当然，CMakeLists.txt中的IMPORTED路径也要做出相应修改。

2、CMakeLists.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 3.10.2)

# Declares and names the project.

project("nativetestdemo")

# 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.
        new_xiaoxu

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s).
        native-lib.cpp)

# 添加so库存放位置
set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../mylibs)

# 添加一个库，它链接我们的so文件
add_library(sotest
        SHARED
        IMPORTED )

# 给sotest这个库设置so文件链接的位置
set_target_properties( sotest
        PROPERTIES IMPORTED_LOCATION
        ../../../../mylibs/${ANDROID_ABI}/libnative_xiaoxu.so )

# 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.
        new_xiaoxu
        sotest
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

主要代码就在注释部分。

3、添加.h文件

将上篇文章中的NativeImpl.h放到cpp文件夹下。

4、native-lib.cpp

#include <jni.h>
#include <string>
#include "NativeImpl.h"

/* 获取NativeImpl */
NativeImpl nativeImpl;
NativeImpl* getNativeImpl(){
    return &nativeImpl;
}

extern "C" JNIEXPORT jstring JNICALL
Java_com_wm_auto_nativetestdemo_NativeImpl_getUserName(
        JNIEnv* env,
        jclass clazz) {
    char* c = getNativeImpl()->getUserName();
    return env->NewStringUTF(c);
}

这里的代码基本没有变化，但之前getUserName()是cpp下NativeImpl.cpp中的方法，而这里是so库中里NativeImpl.cpp中的方法。

5、Java代码NativeImpl

public class NativeImpl {
    // 加载so库
    static {
        System.loadLibrary("new_xiaoxu");
    }

    /**
     * 添加 native 方法
     */
    public static native String getUserName();
}

只修改了加载库