Android Studio使用JNI

1. 添加native接口

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

private native int Add(double num1,double num2);
private native int Sub(double num1,double num2);
private native int Mul(double num1,double num2);
private native int Div(double num1,double num2);

2.Build->Make Project
验证工程中并无其他错误，并对工程进行编译，生成.class文件
在Build/intermediates/classes/debug里面

3.javah 生成.h文件

在工程的app/src/main/java 目录下
cmd 执行 javah com.example.caculate.MainActivity 命令，就会生成.h文件
建立jni目录，将.h拷贝进去

4.jni目录下实现.c
新建一个.c 实现.h中的函数

5.Build->Make Project

会报错
在local.properties文件中增加ndk的路径
sdk.dir=C\:\\Users\\Alif\\AppData\\Local\\Android\\Sdk
ndk.dir=I\:\\Android\\android-ndk-r11c

在app下面的build.gradle里面增加 so的名称
\app\build.gradle
ndk {
moduleName "JniTest"
abiFilters "armeabi", "armeabi-v7a", "x86"
}

6.Build->Make Project 就可以编译出so文件了
生成的so在app/Build/intermediates/ndk/debug/lib下面

我们在jni目录下增加一个Android.mk文件
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := JniTest
LOCAL_SRC_FILES := main.c
include $(BUILD_SHARED_LIBRARY)

然后ndk-build 生成libs目录

将libs目录名称改为 jniLibs 就会自动打包到apk里面了

.h和.c文件

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_example_caculate_MainActivity */

#ifndef _Included_com_example_caculate_MainActivity
#define _Included_com_example_caculate_MainActivity
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_example_caculate_MainActivity
 * Method:    Add
 * Signature: (DD)I
 */
JNIEXPORT jint JNICALL Java_com_example_caculate_MainActivity_Add
  (JNIEnv *, jobject, jdouble, jdouble);

/*
 * Class:     com_example_caculate_MainActivity
 * Method:    Sub
 * Signature: (DD)I
 */
JNIEXPORT jint JNICALL Java_com_example_caculate_MainActivity_Sub
  (JNIEnv *, jobject, jdouble, jdouble);

/*
 * Class:     com_example_caculate_MainActivity
 * Method:    Mul
 * Signature: (DD)I
 */
JNIEXPORT jint JNICALL Java_com_example_caculate_MainActivity_Mul
  (JNIEnv *, jobject, jdouble, jdouble);

/*
 * Class:     com_example_caculate_MainActivity
 * Method:    Div
 * Signature: (DD)I
 */
JNIEXPORT jint JNICALL Java_com_example_caculate_MainActivity_Div
  (JNIEnv *, jobject, jdouble, jdouble);

#ifdef __cplusplus
}
#endif
#endif

#include <jni.h>
#define jintJNICALL
#ifndef _Included_com_example_caculate_MainActivity
#define _Included_com_example_caculate_MainActivity
#ifdef __cplusplus
extern "C" {
#endif

JNIEXPORT jintJNICALL Java_com_example_caculate_MainActivity_Add
        (JNIEnv *env, jobject obj, jdouble num1, jdouble num2)
{
    return (jint)(num1 + num2);
}

JNIEXPORT jintJNICALL Java_com_example_caculate_MainActivity_Sub
        (JNIEnv *env, jobject obj, jdouble num1, jdouble num2)
{
    return (jint)(num1 - num2);
}

JNIEXPORT jintJNICALL Java_com_example_caculate_MainActivity_Mul
        (JNIEnv *env, jobject obj, jdouble num1, jdouble num2)
{
    return (jint)(num1 * num2);
}

JNIEXPORT jintJNICALL Java_com_example_caculate_MainActivity_Div
        (JNIEnv *env, jobject obj, jdouble num1, jdouble num2)
{
    if (num2 == 0) return 0;
    return (jint)(num1 / num2);
}
#ifdef __cplusplus
}
#endif
#endif

使用动态注册JNI

1.函数名称太长，因为是javah生成的头文件，名称太长
2.每一个类都要javah一次，很麻烦

在jni目录下生成编写.c

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

JNIEXPORT jint JNICALL native_Add
(JNIEnv *env, jobject obj, jdouble num1, jdouble num2)
{
return (jint)(num1 + num2 +1);
}

JNIEXPORT jint JNICALL native_Sub
        (JNIEnv *env, jobject obj, jdouble num1, jdouble num2)
{
    return (jint)(num1 - num2 +1);
}

JNIEXPORT jint JNICALL native_Mul
        (JNIEnv *env, jobject obj, jdouble num1, jdouble num2)
{
    return (jint)(num1 * num2 +1);
}

JNIEXPORT jint JNICALL native_Div
        (JNIEnv *env, jobject obj, jdouble num1, jdouble num2)
{
    if (num2 == 0) return 0;
    return (jint)(num1 / num2 +1);
}

//Java和JNI函数的绑定表
static JNINativeMethod gMethods[] = {
        {"Add", "(DD)I", (void *)native_Add},
        {"Sub", "(DD)I", (void *)native_Sub},
        {"Mul", "(DD)I", (void *)native_Mul},
        {"Div", "(DD)I", (void *)native_Div},
};

//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;
}

int register_ndk_load(JNIEnv *env)
{

    return registerNativeMethods(env, "com/example/caculate/MainActivity",
                                 gMethods,sizeof(gMethods) / sizeof(gMethods[0]));
                                 //NELEM(gMethods));
}

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;
}

编写Android.mk文件

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_PRELINK_MODULE := false
LOCAL_MODULE := JniTest_jni
LOCAL_SRC_FILES := MyJniCalc.c
LOCAL_SHARED_LIBRARIES := libandroid_runtime
include $(BUILD_SHARED_LIBRARY)

使用ndk-build生成so文件

还是移到jniLibs目录下

最后成功修改

78+11 +1 = 90

源码：http://pan.baidu.com/s/1kULyvDd   密码 m8ns