# include <inttypes.h>      /* C99 */
typedef uint8_t         jboolean;       /* unsigned 8 bits */
typedef int8_t          jbyte;          /* signed 8 bits */
typedef uint16_t        jchar;          /* unsigned 16 bits */
typedef int16_t         jshort;         /* signed 16 bits */
typedef int32_t         jint;           /* signed 32 bits */
typedef int64_t         jlong;          /* signed 64 bits */
typedef float           jfloat;         /* 32-bit IEEE 754 */
typedef double          jdouble;        /* 64-bit IEEE 754 */
#else
typedef unsigned char   jboolean;       /* unsigned 8 bits */
typedef signed char     jbyte;          /* signed 8 bits */
typedef unsigned short  jchar;          /* unsigned 16 bits */
typedef short           jshort;         /* signed 16 bits */
typedef int             jint;           /* signed 32 bits */
typedef long long       jlong;          /* signed 64 bits */
typedef float           jfloat;         /* 32-bit IEEE 754 */
typedef double          jdouble;        /* 64-bit IEEE 754 */
#endif
/* "cardinal indices and sizes" */
typedef jint            jsize;
#ifdef __cplusplus
/*
* Reference types, in C++
*/
class _jobject {};
class _jclass : public _jobject {};
class _jstring : public _jobject {};
class _jarray : public _jobject {};
class _jobjectArray : public _jarray {};
class _jbooleanArray : public _jarray {};
class _jbyteArray : public _jarray {};
class _jcharArray : public _jarray {};
class _jshortArray : public _jarray {};
class _jintArray : public _jarray {};
class _jlongArray : public _jarray {};
class _jfloatArray : public _jarray {};
class _jdoubleArray : public _jarray {};
class _jthrowable : public _jobject {};
typedef _jobject*       jobject;
typedef _jclass*        jclass;
typedef _jstring*       jstring;
typedef _jarray*        jarray;
typedef _jobjectArray*  jobjectArray;
typedef _jbooleanArray* jbooleanArray;
typedef _jbyteArray*    jbyteArray;
typedef _jcharArray*    jcharArray;
typedef _jshortArray*   jshortArray;
typedef _jintArray*     jintArray;
typedef _jlongArray*    jlongArray;
typedef _jfloatArray*   jfloatArray;
typedef _jdoubleArray*  jdoubleArray;
typedef _jthrowable*    jthrowable;
typedef _jobject*       jweak;
#else /* not __cplusplus */
/*
* Reference types, in C.
*/
typedef void*           jobject;
typedef jobject         jclass;
typedef jobject         jstring;
typedef jobject         jarray;
typedef jarray          jobjectArray;
typedef jarray          jbooleanArray;
typedef jarray          jbyteArray;
typedef jarray          jcharArray;
typedef jarray          jshortArray;
typedef jarray          jintArray;
typedef jarray          jlongArray;
typedef jarray          jfloatArray;
typedef jarray          jdoubleArray;
typedef jobject         jthrowable;
typedef jobject         jweak;
#endif /* not __cplusplus */

我们经常用到的是JNIEnv*，它是一个c结构体，封装了许多常用的函数，如：

struct _JNIEnv {
/* do not rename this; it does not seem to be entirely opaque */
const struct JNINativeInterface* functions;
#if defined(__cplusplus)
jint GetVersion()
{ return functions->GetVersion(this); }
jclass DefineClass(const char *name, jobject loader, const jbyte* buf,
jsize bufLen)
{ return functions->DefineClass(this, name, loader, buf, bufLen); }
jclass FindClass(const char* name)
{ return functions->FindClass(this, name); }
// 这里省略其他函数...
}

cocos2d-x引擎对jni的操作进行了封装，提供了一个非常好用的类:JniHelper，定义了一些常用的接口，该文件位于cocos2dx/platform/android/jni目录下。下面看看JniHelper.h源码：

typedef struct JniMethodInfo_
{
JNIEnv *    env;
jclass      classID;
jmethodID   methodID;
} JniMethodInfo;
class CC_DLL JniHelper
{
public:
static JavaVM* getJavaVM();
static void setJavaVM(JavaVM *javaVM);
static const char* getExternalAssetPath();
static void setExternalAssetPath(const char* externalAssetPath);
static jclass getClassID(const char *className, JNIEnv *env=0);
static bool getStaticMethodInfo(JniMethodInfo &methodinfo, const char *className, const char *methodName, const char *paramCode);
static bool getMethodInfo(JniMethodInfo &methodinfo, const char *className, const char *methodName, const char *paramCode);
static std::string jstring2string(jstring str);
private:
static JavaVM *m_psJavaVM;
static std::string m_externalAssetPath;
};

下面来解释JniHelper的两个常用函数：
(1)getStaticMethodInfo
用来判断Java的类静态函数是否存在，并初始化结构体JniMethodInfo，该结构体封装了JNIEnv*和java.lang.Class对象、函数ID。这样就可以使用JNIEnv*调用 CallStaticXXXMethod(jclass clazz, jmethodID methodID, …)和 CallXXXMethod(jobject obj, jmethodID methodID, …)等常用函数(XXX替换为函数返回值类型，如：Void，Int等)。
第一个参数为JniMethodInfo，第二个参数是类的绝对路径，第三个参数是函数名，第四个参数是函数签名(参数和返回类型)，示例代码如下：

if(JniHelper::getStaticMethodInfo(t, CLASS_NAME, "showTipDialog", "(Ljava/lang/String;Ljava/lang/String;)V"))
{
//...
}

private static Handler mHandler;
public static void init(Handler handler)
{
JniTestHelper.mHandler = handler;
}
public static native void setPackageName(String packageName);

(3)打开JniTest.java，在onCreate函数中添加下面的代码：

protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
JniTestHelper.init(mHandler);
JniTestHelper.setPackageName(this.getPackageName());
}

(4)java层的代码已经完成了，下面来编写jni层代码，在/jni/hellocpp/下创建test.h和test.cpp文件，test.h文件暂时不添加任何函数，代码如下：

#ifndef TEST_H
#define TEST_H
#endif

test.cpp

#include "cocos2d.h"
#include <jni.h>
#include "platform/android/jni/JniHelper.h"
#include "test.h"
#include "JniTest.h"
#define CLASS_NAME "com/alexzhou/jni/JniTestHelper"
using namespace cocos2d;
extern "C"
{
void Java_com_alexzhou_jni_JniTestHelper_setPackageName(JNIEnv *env, jobject thiz, jstring packageName)
{
const char *pkgName = env->GetStringUTFChars(packageName, NULL);
setPackageName(pkgName);
env->ReleaseStringUTFChars(packageName, pkgName);
}
}

必须加上extern “C”，声明以c语言的方式进行编译，因为c++和c在编译时生成的函数签名不一样，可以在网上查找相关资料，不然运行的时候会出现链接错误。
(5)现在编写c++函数，在Classes目录下创建JniTest.h，代码如下：

#ifndef JNI_TEST_H
#define JNI_TEST_H
#include "cocos2d.h"
using namespace cocos2d;
void setPackageName(const char *packageName)
{
CCLog("packageName: %s", packageName);
}
#endif

(6)修改jni/Android.mk文件的LOCAL_SRC_FILES值 ，内容如下：

LOCAL_SRC_FILES := hellocpp/main.cpp \
hellocpp/test.cpp

(7)编译运行，因为我是使用cygwin编译的，而且Android项目不在cocos2d-x的根目录下，所以需要修改build_native.sh，修改COCOS2DX_ROOT和NDK_MODULE_PATH的值，把当前cocos2d-x项目的路径添加到NDK_MODULE_PATH，修改后的值：

COCOS2DX_ROOT="/cygdrive/e/cocos2d-x/cocos2d-2.0-x-2.0.4"
"NDK_MODULE_PATH=${COCOS2DX_ROOT}:${COCOS2DX_ROOT}/cocos2dx/platform/third_party/android/prebuilt:${APP_ROOT}"

运行结果：

public static native void exitApp();
private static void showTipDialog(final String title, final String text)
{
Message msg = mHandler.obtainMessage();
msg.what = JniTest.SHOW_DIALOG;
DialogMessage dm = new DialogMessage();
dm.title = title;
dm.msg = text;
msg.obj = dm;
msg.sendToTarget();
}

(9)创建一个DialogMessage.java,封装dialog要显示的数据。

/**
author:alexzhou
email :zhoujiangbohai@163.com
date  :2012-12-14
**/
public class DialogMessage {
public String title;
public String msg;
}

(10) 修改JniTest.java，添加显示对话框的函数：

public static final int SHOW_DIALOG = 0x0001;
private Handler mHandler = new Handler()
{
@Override
public void handleMessage(Message msg) {
switch(msg.what)
{
case SHOW_DIALOG:
DialogMessage dm = (DialogMessage)msg.obj;
new AlertDialog.Builder(JniTest.this)
.setTitle(dm.title)
.setMessage(dm.msg).setNegativeButton("cancle", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
})
.setPositiveButton("Ok",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
JniTestHelper.exitApp();
}
})
.create().show();
break;
}
}
};

(11)在test.h和test.cpp中添加显示对话框的接口：
test.h

extern "C"
{
void showTipDialog(const char *title, const char *msg);
}

test.cpp

extern "C"
{
void showTipDialog(const char *title, const char *msg)
{
JniMethodInfo t;
if(JniHelper::getStaticMethodInfo(t, CLASS_NAME, "showTipDialog", "(Ljava/lang/String;Ljava/lang/String;)V"))
{
jstring jTitle = t.env->NewStringUTF(title);
jstring jMsg = t.env->NewStringUTF(msg);
t.env->CallStaticVoidMethod(t.classID, t.methodID, jTitle, jMsg);
t.env->DeleteLocalRef(jTitle);
t.env->DeleteLocalRef(jMsg);
}
}
void Java_com_alexzhou_jni_JniTestHelper_setPackageName(JNIEnv *env, jobject thiz, jstring packageName)
{
const char *pkgName = env->GetStringUTFChars(packageName, NULL);
setPackageName(pkgName);
env->ReleaseStringUTFChars(packageName, pkgName);
}
void Java_com_alexzhou_jni_JniTestHelper_exitApp(JNIEnv *env, jobject thiz)
{
exitApp();
}
}

(12) 修改Classes目录下的JniTest.h，添加代码：

void exitApp()
{
CCDirector::sharedDirector()->end();
}

(13)到此为止，所有代码都已经完成了，代码比较简单就不详细解释了，现在编译运行，效果如下：