Android JNI项目创建,方法梳理以及生成So库

简介

项目需要涉及到JNI调用C++ 代码所以所以学习了一了一下Android Studio 工具下 Cmake方式的 Jni 调用的一些知识特此记录一下

环境版本

• Android Studio 4.1.3
• Gradle 4.1.3
• Cmake 3.10.2
• ndk 21.1.6352462
• buildToolsVersion 30.0.3

1.项目配置

plugins {
    id 'com.android.application'
    id 'kotlin-android'
}

android {
    compileSdkVersion 31
// 31.0.0 版本有异常不能用
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.wkq.cdemo"
        minSdkVersion 21
        targetSdkVersion 31
        versionCode 1
        versionName "1.0"
        //设置NDK版本(生成动态so库的时候要用)
        ndkVersion "21.1.6352462"
        // gradle 执行的任务名字
        externalNativeBuild {
            cmake {
                cppFlags ""
                // 过滤生成的库类型
//                abiFilters 'armeabi-v7a'
                //  库格式'armeabi-v7a', 'arm64-v8a', 'x86', 'x86_64'
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
//生成指定版本的 CMakeLists.txt 文件
    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

dependencies {

    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    implementation 'androidx.core:core-ktx:1.7.0'
    implementation 'androidx.appcompat:appcompat:1.4.0'
    implementation 'com.google.android.material:material:1.4.0'
}

文件.png

2.CMakeLists 文件介绍

# 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.
#设置CMake的最低版本
cmake_minimum_required(VERSION 3.10.2)

# Declares and names the project.
project("cdemo")


#这些 native-lib.cpp资源打包设置成一个名为hellow 的共享库（SHARED 替换为STATIC则设置为静态库）
#  native-lib.cpp  
add_library( # Sets the name of the library.
        hellow
        # Sets the library as a shared library.
        SHARED
        # Provides a relative path to your source file(s).
        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.

#（设置要链接的库文件的名称 hellow）
target_link_libraries( # Specifies the target library.
        hellow

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

3.cpp 文件简介

// include 是导包
#include <jni.h>
#include <string>
// extern "C" :C++兼容C代码的
// JNIEXPORT  类似于public修饰符
// JNICALL   用来表示函数的调用规范
// jstring  返回数据类型 这里是String
// Java_<包名>_<类名>_<方法名>
extern "C"
JNIEXPORT jstring JNICALL Java_com_wkq_cdemo_MyJniUtil_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "1122211";
    return env->NewStringUTF(hello.c_str());
}

4. JNI 工具类

package com.wkq.cdemo;

/**
 * @author wkq
 * @date 2022年06月28日 16:46
 * @des
 */

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

    //  jni 调用
    public  static native String stringFromJNI();

}

5.调用

 String content=MyJniUtil.stringFromJNI();

6.生成动态So库

生成动态So库有两种方式

• make project

• Gradle任务中执行 externalNativeBuildRelease/externalNativeBuildRelease或者externalNativeBuildDebug 任务

  
  生成方式.png
  结果.png

总结

简单的梳理了C++类型项目中一些配置,然后生成了动态的So库.
那些打不死我的终将使我强大,继续死磕JNI

资源

1.Demo地址