本博客主要是在Ubuntu 下开发，且默认你已经安装了Eclipse，Android SDK， Android NDK， CDT插件。
在Eclipse中添加配置NDK，路径如下Eclipse->Window->Preferences->Android->NDK ，选择NDK的路径，然后Apply即可。
新建一个名为AndroidJNI_Object的Android工程，新建一个jni的文件夹，其目录下文件树列表如下：
├── jni
│ ├── Android.mk
│ ├── Application.mk
│ └── object
│ ├── Android.mk
│ ├── logger.h
│ └── object_jni.c
jni/Application.mk文件内容如下：
APP_ABI := all
jni/Android.mk，主要用来指定顺序执行所有子文件夹下面的makefile文件，内容如下：
include $(call all-subdir-makefiles)
jni/object/Android.mk，主要用来指定需要编译出的动态库的名称，以及需要编译的源文件，内容如下：
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := object_jni
LOCAL_SRC_FILES := object_jni.c LOCAL_LDLIBS := -llog include $(BUILD_SHARED_LIBRARY)
jni/object/logger.h 主要用来在JNI层打印日志，内容如下：
#include <jni.h>
#include <android/log.h> /**
* 定义log标签
*/
#define TAG "jni_logger" /**
* 定义info信息
*/
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, TAG, __VA_ARGS__) /**
* 定义debug信息
*/
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, TAG, __VA_ARGS__) /**
* 定义error信息
*/
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, TAG, __VA_ARGS__)
jni/object/object_jni.c，主要用来注册绑定java函数和native函数，以及java函数在c中相应函数的具体实现， 内容如下：
#include "logger.h" #ifndef NULL
#define NULL ((void *) 0)
#endif /**
* 获取数组的大小
*/
#define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0]))) /**
* 指定要注册的类，对应的完整的java类名
*/
#define JNIREG_CLASS "com/clarck/jni/MainActivity"
#define JNIPAR_CLASS "com/clarck/jni/Person" struct PersonOffsets
{
jfieldID name;
jfieldID age;
jfieldID height;
} gPersonOffsets; typedef struct tagPerson
{
char mName[];
int mAge;
float mHeight;
} Person; static Person gPersons[] = {
{"clarck", , },
{"lilei", , },
{"hanmeimei", , },
}; #define GPERSON_NUM NELEM(gPersons) JNIEXPORT jint JNICALL native_object(JNIEnv *env, jobject clazz, jobject person, jint index) {
if ((int) index < || (int) index >= GPERSON_NUM)
return -; //将Person数组中的第index个成员赋值给pPerson指针
Person *pPerson = &gPersons[index];
//设置java对象的person的mName
jstring name = (*env)->NewStringUTF(env, pPerson->mName);
(*env)->SetObjectField(env, person, gPersonOffsets.name, name);
//设置java对象person的mAge
(*env)->SetIntField(env, person, gPersonOffsets.age, pPerson->mAge);
//设置java对象person的mHeight
(*env)->SetFloatField(env, person, gPersonOffsets.height, pPerson->mHeight); LOGD("%s index-%d mName:%s, mAge:%d, mHeight:%f\n",
__func__, index, pPerson->mName, pPerson->mAge, pPerson->mHeight); return ;
} static void nativeClassInit(JNIEnv *env) {
jclass personClass = (*env)->FindClass(env, JNIPAR_CLASS);
gPersonOffsets.name = (*env)->GetFieldID(env, personClass, "mName", "Ljava/lang/String;");
gPersonOffsets.age = (*env)->GetFieldID(env, personClass, "mAge", "I");
gPersonOffsets.height = (*env)->GetFieldID(env, personClass, "mHeight", "F");
} /**
* Java和JNI函数绑定
*/
static JNINativeMethod method_table[] = {
{ "getPersonInfoByIndex", "(Lcom/clarck/jni/Person;I)I", (void*) native_object },
}; /**
* 注册native方法到java中
*/
static int registerNativeMethods(JNIEnv* env, const char* className,
JNINativeMethod* gMethods, int numMethods) {
jclass clazz;
clazz = (*env)->FindClass(env, className);
if (clazz == NULL) {
return JNI_FALSE;
} if ((*env)->RegisterNatives(env, clazz, gMethods, numMethods) < ) {
return JNI_FALSE;
} return JNI_TRUE;
} /**
* 调用注册方法
*/
int register_ndk_load(JNIEnv* env) {
nativeClassInit(env);
return registerNativeMethods(env, JNIREG_CLASS, method_table,
NELEM(method_table));
} JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* reserved) {
JNIEnv* env = NULL;
jint result = -; if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {
return result;
} register_ndk_load(env); //返回jni的版本
return JNI_VERSION_1_4;
}
接着在Project中右键Android Tools->Add Native Support，最后java层调用如下：
package com.clarck.jni; import android.app.Activity;
import android.os.Bundle;
import android.util.Log; public class MainActivity extends Activity {
private Person mPerson = null; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); Log.d("Test", "onCreate");
mPerson = new Person();
for (int i = 0; i < 3; i++) {
getPersonInfoByIndex(mPerson, i);
Log.d("Test", "mPersion[" + i + "] -- " + mPerson);
}
} private native int getPersonInfoByIndex(Person person, int index); static {
System.loadLibrary("object_jni");
} }
package com.clarck.jni;
public class Person {
private String mName;
private int mAge;
private float mHeight;
@Override
public String toString() {
return "mName: " + mName + ", mAge: " + mAge + ", mHeight: " + mHeight;
}
}
运行结果如下:
04-15 15:37:30.916: D/Test(31477): onCreate
04-15 15:37:30.916: D/jni_logger(31477): native_object index-0 mName:clarck, mAge:25, mHeight:175.000000
04-15 15:37:30.916: D/Test(31477): mPersion[0] -- mName: clarck, mAge: 25, mHeight: 175.0
04-15 15:37:30.916: D/jni_logger(31477): native_object index-1 mName:lilei, mAge:30, mHeight:166.000000
04-15 15:37:30.916: D/Test(31477): mPersion[1] -- mName: lilei, mAge: 30, mHeight: 166.0
04-15 15:37:30.916: D/jni_logger(31477): native_object index-2 mName:hanmeimei, mAge:51, mHeight:172.000000
04-15 15:37:30.916: D/Test(31477): mPersion[2] -- mName: hanmeimei, mAge: 51, mHeight: 172.0