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