JNI入门笔记-编译和使用so文件

1. 声明native方法

public class CruiseApi {
    public static native void init();
    public static native void start();
    public static native void stop();
    public static native void resume();
    ...
}

2. 命令行进入xxx\YourProject\app\src\main\java目录

3. 执行javah -jni [class],class为完整路径

如果文件内有中文注释，会出现以下错误，去掉即可

4. 然后xxx\YourProject\app\src\main\java目录下会生成一个xxx.h文件

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_woosiyuan_cruiserobot_algorithm_CruiseApi */

#ifndef _Included_com_woosiyuan_cruiserobot_algorithm_CruiseApi
#define _Included_com_woosiyuan_cruiserobot_algorithm_CruiseApi
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    init
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_init
  (JNIEnv *, jclass);

/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    start
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_start
  (JNIEnv *, jclass);

/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    stop
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_stop
  (JNIEnv *, jclass);

/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    resume
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_resume
  (JNIEnv *, jclass);

...省略其它方法

#ifdef __cplusplus
}
#endif
#endif

5. 在xxx\YourProject\app\src\main目录下新建jni文件夹

5.1. 把上一步生成的xxx.h文件放进来

5.2. 创建*.c文件,文件名可根据你的业务逻辑进行命名即可。然后把生成的.h文件里面的方法在这里进行实现，这里只是打印一下日志

#include <jni.h>
#include "com_woosiyuan_cruiserobot_algorithm_CruiseApi.h"

#include <android/log.h>
#define LOG_TAG "CruiseRobot_algorithm"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)

/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    init
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_init
(JNIEnv *env, jclass cls){
    LOGD("hello world - init");
}


/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    start
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_start
(JNIEnv *env, jclass cls){
    LOGD("hello world - start");
}

/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    stop
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_stop
(JNIEnv *env, jclass cls){
LOGD("hello world - stop");
}

/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    resume
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_resume
(JNIEnv *env, jclass cls){
LOGD("hello world - resume");
}

/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    getPosition
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_getPosition
        (JNIEnv *env, jclass cls){
    LOGD("hello world - getPosition");
    jstring rtstr = (*env)->NewStringUTF(env, "hello world - getPosition");
    return rtstr;
}

/*
 * Class:     com_woosiyuan_cruiserobot_algorithm_CruiseApi
 * Method:    detectPosition
 * Signature: ()C
 */
JNIEXPORT jchar JNICALL Java_com_woosiyuan_cruiserobot_algorithm_CruiseApi_detectPosition
        (JNIEnv *env, jclass cls){
    LOGD("hello world - detectPosition");
    return 0;
}
...

5.3. 创建Android.mk文件

LOCAL_PATH: 是描述所有要编译的C文件所在的根目录，这边的赋值为$(call my-dir)，代表根目录即为Android.mk所在的目录。
include $(CLEAR_VARS): 清除之前的一些系统变量。
LOCAL_MODULE: 编译的目标对象，生成后会加上前缀lib和后缀.so。
LOCAL_SRC_FILES: 编译的源文件,就是上一步创建的.c文件
include $(BUILD_SHARED_LIBRARY): 指明要编译成动态库

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := cruise
LOCAL_SRC_FILES := CruiseAlgorithm.c
LOCAL_LDLIBS    := -llog

include $(BUILD_SHARED_LIBRARY)

6. 编译生成.so文件

命令行进入xxx\YourProject\app\src\main\jni目录,执行命令ndk-build

7. 添加.so文件到项目中，调用方法进行测试

7.1. 在第一步的native方法中加载.so文件

public class CruiseApi {
    static {
        System.loadLibrary("cruise");
    }
    public static native void init();
    public static native void start();
    public static native void stop();
    public static native void resume();
    ...
}

7.2. 调用native方法进行测试

    private void testCruise(){
        CruiseApi.init();
        CruiseApi.start();
        CruiseApi.stop();
        CruiseApi.resume();
        ...
    }

控制台输入日志，表示调用成功