Android(安卓)NDK 学习之传递类对象

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_jniLOCAL_SRC_FILES := object_jni.cLOCAL_LDLIBS := -lloginclude $(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[10];    int        mAge;    float    mHeight;} Person;static Person gPersons[] = {        {"clarck", 25, 175},        {"lilei", 30, 166},        {"hanmeimei", 51, 172},};#define GPERSON_NUM NELEM(gPersons)JNIEXPORT jint JNICALL native_object(JNIEnv *env, jobject clazz, jobject person, jint index) {    if ((int) index < 0 || (int) index >= GPERSON_NUM)        return -1;    //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 0;}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) < 0) {        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 = -1;    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): onCreate04-15 15:37:30.916: D/jni_logger(31477): native_object index-0 mName:clarck, mAge:25, mHeight:175.00000004-15 15:37:30.916: D/Test(31477): mPersion[0] -- mName: clarck, mAge: 25, mHeight: 175.004-15 15:37:30.916: D/jni_logger(31477): native_object index-1 mName:lilei, mAge:30, mHeight:166.00000004-15 15:37:30.916: D/Test(31477): mPersion[1] -- mName: lilei, mAge: 30, mHeight: 166.004-15 15:37:30.916: D/jni_logger(31477): native_object index-2 mName:hanmeimei, mAge:51, mHeight:172.00000004-15 15:37:30.916: D/Test(31477): mPersion[2] -- mName: hanmeimei, mAge: 51, mHeight: 172.0

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