Android JNI ,将java 实例与c实例绑定

测试条件：

c++ 中存在class TestA,其中含有属性int a。

java 中存在class TestJni,

TestJni.java代码如下：

public class TestJni {

    public native final void setA(int a);
    public native final void add(int add);
    public native final int getA();
    private int mNativeInJavaObj;
    
    static {
        System.loadLibrary("testjni");
    }
}

TestJni中属性mNativeInJavaObj用来绑定c++中TestA的对象实例，有点像一个ID。


com_zcw_soundtouch_TestJni.cpp代码如下：

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
#include <android/log.h>

#include "testclassa.h"
/* Header for class com_zcw_soundtouch_TestJni */

#define LOGV(...)   __android_log_print((int)ANDROID_LOG_INFO, "SOUNDTOUCH", __VA_ARGS__)
//#define LOGV(...)

// ----------------------------------------------------------------------------

struct fields_t {
    jclass    testAClass;
    jfieldID    context;
};
static fields_t fields;

//static Mutex sLock;

// ----------------------------------------------------------------------------


#ifndef _Included_com_zcw_soundtouch_TestJni
#define _Included_com_zcw_soundtouch_TestJni
#ifdef __cplusplus
extern "C" {
#endif
void persistence(JNIEnv * env, jobject thiz){
    LOGV("called persistence");
    /*
    fields.testAClass = env->FindClass("");
    fields.context = 
        env->GetFieldID(fields.testAClass,
                        "mNativeInJavaObj", "I");
    */
    if(NULL==fields.context){
        fields.testAClass = env->GetObjectClass(thiz);
        fields.context = 
        env->GetFieldID(fields.testAClass,
                        "mNativeInJavaObj", "I");
        
    }
    int value = env->GetIntField(thiz, fields.context);
    if(0!=value){
        LOGV("class TestA is eixts");
        return ;
    }
    LOGV("class TestA is not eixts");
    TestA * testA = new TestA();
    testA->setA(10);
    env->SetIntField(thiz,fields.context, (int)testA);
}
/*
 * Class:     com_zcw_soundtouch_TestJni
 * Method:    setA
 * Signature: (I)V
 */
JNIEXPORT void JNICALL Java_com_zcw_soundtouch_TestJni_setA
  (JNIEnv *env, jobject thiz, jint value)
{
    persistence(env,thiz);
    TestA* testA = (TestA*)env->GetIntField(thiz, fields.context);
    testA->setA((int)value);
}

/*
 * Class:     com_zcw_soundtouch_TestJni
 * Method:    add
 * Signature: (I)V
 */
JNIEXPORT void JNICALL Java_com_zcw_soundtouch_TestJni_add
  (JNIEnv *env, jobject thiz, jint value)
{
    persistence(env,thiz);
    TestA* testA = (TestA*)env->GetIntField(thiz, fields.context);
    testA->addA((int)value);
    
}

/*
 * Class:     com_zcw_soundtouch_TestJni
 * Method:    getA
 * Signature: ()I
 */
JNIEXPORT jint JNICALL Java_com_zcw_soundtouch_TestJni_getA
  (JNIEnv *env, jobject thiz )
{
    persistence(env,thiz);
    TestA* testA = (TestA*)env->GetIntField(thiz, fields.context);
    
    return testA->getA();
}

#ifdef __cplusplus
}
#endif
#endif

testclassa.h

#include<stdio.h>


class TestA{
private:
    int a ;

public:
    TestA();
    ~TestA();
    void setA(int avalue);
    void addA(int add);
    int getA();

};

testclassa.cpp

#include<stdio.h>
#include "testclassa.h"

TestA::TestA(){}
TestA::~TestA(){}


void TestA::setA(int avalue)
{
    a = avalue;
}

void TestA::addA(int add)
{
    a+=add;
}

int TestA::getA()
{
    return a;
}

java测试代码：

Log.e(TAG, "start load jni");
        {
            TestJni testJni = new TestJni();
            Log.e(TAG, "loaded jni");
            testJni.setA(100);
            Log.e(TAG, "setted value ");
            testJni.add(2912);
            int value = testJni.getA();
            Log.e(TAG, "after add:a="+value);
        }
        Log.e(TAG, "===============");
        {
            TestJni testJni = new TestJni();
            Log.e(TAG, "loaded jni");
            testJni.setA(257);
            Log.e(TAG, "setted value ");
            testJni.add(212);
            int value = testJni.getA();
            Log.e(TAG, "after add:a="+value);
        }

打印结果：

10-21 12:52:41.057: E/Main2Activity(13677): loaded jni
10-21 12:52:41.057: I/SOUNDTOUCH(13677): called persistence
10-21 12:52:41.057: I/SOUNDTOUCH(13677): class TestA is not eixts
10-21 12:52:41.057: E/Main2Activity(13677): setted value 
10-21 12:52:41.057: I/SOUNDTOUCH(13677): called persistence
10-21 12:52:41.057: I/SOUNDTOUCH(13677): class TestA is eixts
10-21 12:52:41.057: I/SOUNDTOUCH(13677): called persistence
10-21 12:52:41.057: I/SOUNDTOUCH(13677): class TestA is eixts
10-21 12:52:41.057: E/Main2Activity(13677): after add:a=3012
10-21 12:52:41.057: E/Main2Activity(13677): ===============
10-21 12:52:41.057: E/Main2Activity(13677): loaded jni
10-21 12:52:41.057: I/SOUNDTOUCH(13677): called persistence
10-21 12:52:41.057: I/SOUNDTOUCH(13677): class TestA is not eixts
10-21 12:52:41.057: E/Main2Activity(13677): setted value 
10-21 12:52:41.057: I/SOUNDTOUCH(13677): called persistence
10-21 12:52:41.057: I/SOUNDTOUCH(13677): class TestA is eixts
10-21 12:52:41.057: I/SOUNDTOUCH(13677): called persistence
10-21 12:52:41.057: I/SOUNDTOUCH(13677): class TestA is eixts
10-21 12:52:41.057: E/Main2Activity(13677): after add:a=469