android利用JNI调用C++自定义类

找了好久关于android调用C/C++库的文章，但是始终没有一片是关于android利用jni调用C++自定义类的文章，无奈只好看android的源代码，学习android的图形库的实现，因为它的实现底层也是利用C++的skia库。下面就3个文件来描述。

首先是你在java中的一个类，用于你在应用程序中调用这里取名叫Person类

package whf.jnitest;

public class Person {

    static
    {
        System.loadLibrary("Person");
    }

    private int mNativePerson;

    public Person()
    {
        mNativePerson = init();
    }
    protected void finalize()
    {
        try {
            finalizer(mNativePerson);
        } finally {
            try {
                super.finalize();
            } catch (Throwable e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    public int getAge()
    {
        return native_getAge(mNativePerson);
    }

    public void setAge(int age)
    {
        native_setAge(mNativePerson, age);
    }

    private native void finalizer(int nPerson);
    public  native int  add(int a, int b);
    public  native int  sub(int a, int b);
    private native int  init();

    private native int  native_getAge(int nPerson);
    private native void native_setAge(int nPerson, int age);
}

然后你的C++文件就如下，我定义为CPerson类

#define LOG_TAG "this is a first JNI test"

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <assert.h>
#include "jni.h"
#include "CPerson.h"



    jint add(JNIEnv *env, jobject obj, jint a, jint b)
    {
        return a + b;
    }

    jint Java_whf_jnitest_Person_sub(JNIEnv *env, jobject obj, jint a, jint b)
    {
        return a - b;
    }

    void Java_whf_jnitest_Person_finalizer(JNIEnv *env, jobject clazz, CPerson *obj)
    {
        delete obj;
    }

    CPerson * Java_whf_jnitest_Person_init(JNIEnv *env, jobject clazz)
    {
        CPerson *p = new CPerson();
        return p;
    }

    void Java_whf_jnitest_Person_setAge(JNIEnv *env, jobject clazz, CPerson *obj, jint age)
    {
        return obj->setAge(age);
    }

    jint Java_whf_jnitest_Person_getAge(JNIEnv *env, jobject clazz, CPerson *obj)
    {
        return obj->getAge();
    }

    static JNINativeMethod methods[]{
        {"add", "(II)I", (void *)add},
        {"sub", "(II)I", (void *)Java_whf_jnitest_Person_sub},
        {"finalizer", "(I)V", (void *)Java_whf_jnitest_Person_finalizer},
        {"init", "()I", (void *)Java_whf_jnitest_Person_init},
        {"native_setAge", "(II)V", (void *)Java_whf_jnitest_Person_setAge},
        {"native_getAge", "(I)I", (void *)Java_whf_jnitest_Person_getAge},
    };

    static const char * classPathName = "whf/jnitest/Person";

    static int registerNativeMethods(JNIEnv* env, const char* className,
        JNINativeMethod* gMethods, int numMethods)
    {
        jclass clazz;

        clazz = env->FindClass(className);
        if (clazz == NULL) {
            //LOGE("Native registration unable to find class '%s'", className);
            return JNI_FALSE;
        }
        if (env->RegisterNatives(clazz, gMethods, numMethods) < 0) {
            //LOGE("RegisterNatives failed for '%s'", className);
            return JNI_FALSE;
        }

        return JNI_TRUE;
    }

    static int registerNatives(JNIEnv* env)
    {
      if (!registerNativeMethods(env, classPathName,
                     methods, sizeof(methods) / sizeof(methods[0]))) {
        return JNI_FALSE;
      }

      return JNI_TRUE;
    }

    typedef union {
        JNIEnv* env;
        void* venv;
    } UnionJNIEnvToVoid;

    /* This function will be call when the library first be loaded */
    jint JNI_OnLoad(JavaVM* vm, void* reserved)
    {
        UnionJNIEnvToVoid uenv;
        JNIEnv* env = NULL;
        //LOGI("JNI_OnLoad!");

        if (vm->GetEnv((void**)&uenv.venv, JNI_VERSION_1_4) != JNI_OK) {
            //LOGE("ERROR: GetEnv failed");
            return -1;
        }

        env = uenv.env;;

        //jniRegisterNativeMethods(env, "whf/jnitest/Person", methods, sizeof(methods) / sizeof(methods[0]));

        if (registerNatives(env) != JNI_TRUE) {
            //LOGE("ERROR: registerNatives failed");
            return -1;
        }

         return JNI_VERSION_1_4;
    }

CPerson的声明如下：

#ifndef _CPERSON_H_
#define _CPERSON_H_

class CPerson
{
private:
    int m_age;
public:
    CPerson();
    int getAge();
    void setAge(int age);
};

#endif

这样一个简单的JNI调用C++自定义类就实现了