Android Studio在gradle:3.1.1版本下使用JNI

版权声明：本文为博主原创文章，可以随意转载，但是必须在开头标明出处。 https://blog.csdn.net/qq_29951983/article/details/82431674

一 创建JNI方法

public class JniUtils {
    static {
        //生成的SO文件名
        System.loadLibrary("JNISample");
    }
    public  native String getJniString();
}

二 创建JNI目录

在main下面创建jni目录

三 生成.h头文件

在Terminal窗口中，使用cd命令进入到该
/Users/apple/Downloads/TestJNI/app/build/intermediates/classes/debug
目录下；
使用javah com.example.apple.testjni.JniUtils即可生成.h文件；

四 拷贝生成的.h文件到jni目录下

五 编写.cpp文件

创建一个.cpp文件，名字和.h文件同名即可

#include "com_example_apple_testjni_JniUtils.h"

JNIEXPORT jstring JNICALL Java_com_example_apple_testjni_JniUtils_getJniString
        (JNIEnv *env, jobject jclass) {
    // new 一个字符串，返回Hello World
    return env -> NewStringUTF("yaoyan");
}

六 配置build.gradle

android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "com.example.apple.testjni"
        minSdkVersion 15
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        //添加externalNativeBuild字段
        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
            }
        }

    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    sourceSets { main { jni.srcDirs = ['src/main/jni', 'src/main/jni/'] } }

    externalNativeBuild {
        cmake {
            //在gradle同级别目录下创建该文件
            path "CMakeLists.txt"
        }
    }
}

七 创建cmake文件

八 编写cmake文件

注意

# 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.
#CMakeLists.txt
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.
      # 设置so文件名称.
       JNISample

       # Sets the library as a shared library.
       SHARED
       # 设置这个so文件为共享.

       # Provides a relative path to your source file(s).
       # 设置这个so文件为共享.
       src/main/jni/com_example_apple_testjni_JniUtils.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.
            # 制定目标库.
            JNISample

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

参考链接
Android Studio jni开发入门——看我就够了！
但是这位作者大佬，好像不是gradle3.0以上，按照他操作报错了。