cocos2d-x 经过JNI实现c/c++和Android的java层函数互调
本文主要实现两个功能:
(1)通过Android sdk的API得到应用程序的包名(PackageName),然后传递给c++层函数。
(2)通过c++函数调用Android的java层函数,显示一个对话框,点击按钮退出程序。
1. 首先来简单学习一下JNI的相关知识,我这篇文章中简单实现了怎么在Android Java层调用c++函数。要想使用JNI,必须得包含头文件,android是使用ndk编译c/c++的,这里jni.h文件位于:\android-ndk-r8b\platforms\android-14\arch-arm\usr\include\jni.h,该文件定义了所有和JNI相关的数据类型和接口。下面是相关代码片段:
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#
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:
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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:
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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:
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if (JniHelper::getStaticMethodInfo(t,
CLASS_NAME, "showTipDialog" , "(Ljava/lang/String;Ljava/lang/String;)V" ))
{
//...
}
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关于类型签名,请对照下图:
(2)getMethodInfo
该函数与getStaticMethodInfo类似,用于Java类的非静态函数。
2. 下面开始实现文章开头所述的两个功能,本文是在cocos2d-x 2.0版本 自适应屏幕分辨率demo的基础上添加的。
(1)利用cocos2d-x创建一个Android工程,名为JniTest,包名为com.alexzhou.jni,此时该包下会自动生成一个JniTest.java文件。
(2)首先来实现把应用程序的包名传递给c++函数,在包下创建JniTestHelper.java,该类封装了给c++调用的函数,添加如下代码:
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private static Handler
mHandler;
public static void
init(Handler handler)
{
JniTestHelper.mHandler
= handler;
}
public static native
void
setPackageName(String packageName);
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(3)打开JniTest.java,在onCreate函数中添加下面的代码:
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protected void onCreate(Bundle
savedInstanceState){
super .onCreate(savedInstanceState);
JniTestHelper.init(mHandler);
JniTestHelper.setPackageName( this .getPackageName());
}
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(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:
test.h
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#ifndef
TEST_H
#define
TEST_H
#endif
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test.cpp
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#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);
}
}
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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:
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#ifndef
JNI_TEST_H
#define
JNI_TEST_H
#include
"cocos2d.h"
using namespace cocos2d;
void setPackageName( const char *packageName)
{
CCLog( "packageName:
%s" ,
packageName);
}
#endif
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(6)修改jni/Android.mk文件的LOCAL_SRC_FILES值 ,内容如下:
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LOCAL_SRC_FILES
:= hellocpp /main .cpp
\
hellocpp /test .cpp
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(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:
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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}"
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运行结果:
(8)现在来实现通过c++函数调用java层函数,显示一个对话框。在JniTestHelper.java添加如下代码:
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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();
}
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(9)创建一个DialogMessage.java,封装dialog要显示的数据。
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/**
author:alexzhou
email
:zhoujiangbohai@163.com
date
:2012-12-14
**/
public class DialogMessage
{
public String
title;
public String
msg;
}
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(10) 修改JniTest.java,添加显示对话框的函数:
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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 ;
}
}
};
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(11)在test.h和test.cpp中添加显示对话框的接口:
test.h
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extern "C"
{
void showTipDialog( const char *title,
const char *msg);
}
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test.cpp
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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();
}
}
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(12) 修改Classes目录下的JniTest.h,添加代码:
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void exitApp()
{
CCDirector::sharedDirector()->end();
}
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(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:
免分源码:http://download.csdn.net/detail/kaitiren/6256205
- 1楼suannai0314昨天 10:42
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