C语言JNI的动态注册详解

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.jhzl.a7_jni_2way"
        minSdkVersion 21
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

        externalNativeBuild {
            cmake {
                cppFlags ""
            }
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView addTv = findViewById(R.id.add_tv);
        TextView subTv = findViewById(R.id.sub_tv);
        addTv.setText("加法计算:"+add(10,20));
        subTv.setText("减法计算:"+sub(10,20));
    }
    static {
        //加载静态库
        System.loadLibrary("native-lib");
    }

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

}

# 指定cmke版本
cmake_minimum_required(VERSION 3.4.1)
add_library(native-lib
        SHARED
        src/main/cpp/Hello.cpp) #添加.c源文件
include_directories(src/main/cpp/include) #添加头文件的位置
target_link_libraries(native-lib
        log) #选择要使用的库

#ifndef PRACTICLE_HELLO_H
#define PRACTICLE_HELLO_H
extern "C"
#endif //PRACTICLE_HELLO_H

#include <jni.h>
#include "Hello.h"
#include<android/log.h>
#define TAG "helloworld-jni" // 这个是自定义的LOG的标识
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,TAG ,__VA_ARGS__) // 定义LOGD类型
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,TAG ,__VA_ARGS__) // 定义LOGI类型
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN,TAG ,__VA_ARGS__) // 定义LOGW类型
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,TAG ,__VA_ARGS__) // 定义LOGE类型
#define LOGF(...) __android_log_print(ANDROID_LOG_FATAL,TAG ,__VA_ARGS__) // 定义LOGF类型
#ifdef __cplusplus
extern "C" {
#endif

//对应MainActivity的add
jint add(JNIEnv *env, jobject clazz, jint a, jint b) {
    return a + b;
}

//对应MainActivity的sub
jint sub(JNIEnv *env, jobject clazz, jint a, jint b) {
    return a - b;
}

//回调函数 在这里面注册函数
jint  JNI_OnLoad(JavaVM* vm, void* reserved){
    JNIEnv* env = NULL;
    //env赋值
    LOGD("GetEnv");
    //获取JniEnv
    if(vm->GetEnv((void**)&env,JNI_VERSION_1_6)!= JNI_OK){
        LOGD("GetEnv Failed");
        return -1;
    }
    //获取一个class对象,对应java类MainActivity
    jclass  mainActivity = env->FindClass("com/jhzl/a7_jni_2way/MainActivity");

    
    JNINativeMethod methods_MainActivity[] = {
            {"add", "(II)I", (jint *) add},
            {"sub", "(II)I", (jint *) sub}

    };
    env->RegisterNatives(mainActivity,methods_MainActivity,sizeof(methods_MainActivity)/ sizeof(methods_MainActivity[0]));
    env->RegisterNatives(mainActivity,methods_MainActivity,sizeof(methods_MainActivity)/ sizeof(methods_MainActivity[1]));
    //返回jni 的版本
    return JNI_VERSION_1_6;
}


#ifdef __cplusplus
}
#endif