NDK 使用流程

本文通过一个简单的java调用c语言的例子来介绍NDK的使用流程

使用流程

1. 创建一个Android项目
2. 创建native方法
3. 编译生成头文件 .h 文件
4. 编写c文件
5. 编译c生成so文件，调用

1.创建一个Android项目

2.创建native方法：

public class MainActivity extends Activity {public static native String getStringFromC();@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.activity_main);}}

3.利用NDK编译生成头文件，先cd到Android项目的路径中，用javah命令生成头文件，格式为：

javah -classpath 路径1 -d 路径2

例子：

javah -classpath bin/classes;E:\Eclipse\sdk\platforms\android-19\android.jar -d jni com.example.myhellojni.MainActivity

bin/classes;E:\Eclipse\sdk\platforms\android-19\android.jar              classes文件加 指定一个android.jar包

jni com.example.myhellojni.MainActivity                                                jni 目录加  java文件的包名+类名

图片是我自己的例子，敲回车不报错就说明头文件生成了

头文件如下：

结尾处是自动创建的相应的c函数，格式是Java_包名_类名_方法名

/* DO NOT EDIT THIS FILE - it is machine generated */#include <jni.h>/* Header for class com_example_myhellojni_MainActivity */#ifndef _Included_com_example_myhellojni_MainActivity#define _Included_com_example_myhellojni_MainActivity#ifdef __cplusplusextern "C" {#endif#undef com_example_myhellojni_MainActivity_MODE_PRIVATE#define com_example_myhellojni_MainActivity_MODE_PRIVATE 0L#undef com_example_myhellojni_MainActivity_MODE_WORLD_READABLE#define com_example_myhellojni_MainActivity_MODE_WORLD_READABLE 1L#undef com_example_myhellojni_MainActivity_MODE_WORLD_WRITEABLE#define com_example_myhellojni_MainActivity_MODE_WORLD_WRITEABLE 2L#undef com_example_myhellojni_MainActivity_MODE_APPEND#define com_example_myhellojni_MainActivity_MODE_APPEND 32768L#undef com_example_myhellojni_MainActivity_MODE_MULTI_PROCESS#define com_example_myhellojni_MainActivity_MODE_MULTI_PROCESS 4L#undef com_example_myhellojni_MainActivity_MODE_ENABLE_WRITE_AHEAD_LOGGING#define com_example_myhellojni_MainActivity_MODE_ENABLE_WRITE_AHEAD_LOGGING 8L#undef com_example_myhellojni_MainActivity_BIND_AUTO_CREATE#define com_example_myhellojni_MainActivity_BIND_AUTO_CREATE 1L#undef com_example_myhellojni_MainActivity_BIND_DEBUG_UNBIND#define com_example_myhellojni_MainActivity_BIND_DEBUG_UNBIND 2L#undef com_example_myhellojni_MainActivity_BIND_NOT_FOREGROUND#define com_example_myhellojni_MainActivity_BIND_NOT_FOREGROUND 4L#undef com_example_myhellojni_MainActivity_BIND_ABOVE_CLIENT#define com_example_myhellojni_MainActivity_BIND_ABOVE_CLIENT 8L#undef com_example_myhellojni_MainActivity_BIND_ALLOW_OOM_MANAGEMENT#define com_example_myhellojni_MainActivity_BIND_ALLOW_OOM_MANAGEMENT 16L#undef com_example_myhellojni_MainActivity_BIND_WAIVE_PRIORITY#define com_example_myhellojni_MainActivity_BIND_WAIVE_PRIORITY 32L#undef com_example_myhellojni_MainActivity_BIND_IMPORTANT#define com_example_myhellojni_MainActivity_BIND_IMPORTANT 64L#undef com_example_myhellojni_MainActivity_BIND_ADJUST_WITH_ACTIVITY#define com_example_myhellojni_MainActivity_BIND_ADJUST_WITH_ACTIVITY 128L#undef com_example_myhellojni_MainActivity_CONTEXT_INCLUDE_CODE#define com_example_myhellojni_MainActivity_CONTEXT_INCLUDE_CODE 1L#undef com_example_myhellojni_MainActivity_CONTEXT_IGNORE_SECURITY#define com_example_myhellojni_MainActivity_CONTEXT_IGNORE_SECURITY 2L#undef com_example_myhellojni_MainActivity_CONTEXT_RESTRICTED#define com_example_myhellojni_MainActivity_CONTEXT_RESTRICTED 4L#undef com_example_myhellojni_MainActivity_RESULT_CANCELED#define com_example_myhellojni_MainActivity_RESULT_CANCELED 0L#undef com_example_myhellojni_MainActivity_RESULT_OK#define com_example_myhellojni_MainActivity_RESULT_OK -1L#undef com_example_myhellojni_MainActivity_RESULT_FIRST_USER#define com_example_myhellojni_MainActivity_RESULT_FIRST_USER 1L#undef com_example_myhellojni_MainActivity_DEFAULT_KEYS_DISABLE#define com_example_myhellojni_MainActivity_DEFAULT_KEYS_DISABLE 0L#undef com_example_myhellojni_MainActivity_DEFAULT_KEYS_DIALER#define com_example_myhellojni_MainActivity_DEFAULT_KEYS_DIALER 1L#undef com_example_myhellojni_MainActivity_DEFAULT_KEYS_SHORTCUT#define com_example_myhellojni_MainActivity_DEFAULT_KEYS_SHORTCUT 2L#undef com_example_myhellojni_MainActivity_DEFAULT_KEYS_SEARCH_LOCAL#define com_example_myhellojni_MainActivity_DEFAULT_KEYS_SEARCH_LOCAL 3L#undef com_example_myhellojni_MainActivity_DEFAULT_KEYS_SEARCH_GLOBAL#define com_example_myhellojni_MainActivity_DEFAULT_KEYS_SEARCH_GLOBAL 4L/* * Class:     com_example_myhellojni_MainActivity * Method:    getStringFromC * Signature: ()Ljava/lang/String; */JNIEXPORT jstring JNICALL Java_com_example_myhellojni_MainActivity_getStringFromC  (JNIEnv *, jclass);#ifdef __cplusplus}#endif#endif

4.编写c文件  

返回一个字符串

hello.c

#include<stdio.h>#include<stdlib.h>#include "com_example_myhellojni_MainActivity.h"JNIEXPORT jstring JNICALL Java_com_example_myhellojni_MainActivity_getStringFromC(JNIEnv *env, jclass jclass) {return (*env)->NewStringUTF(env, "Hello NDK");}

在Android.mk指定编译名

# Copyright (C) 2009 The Android Open Source Project## Licensed under the Apache License, Version 2.0 (the "License");# you may not use this file except in compliance with the License.# You may obtain a copy of the License at##      http://www.apache.org/licenses/LICENSE-2.0## Unless required by applicable law or agreed to in writing, software# distributed under the License is distributed on an "AS IS" BASIS,# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.# See the License for the specific language governing permissions and# limitations under the License.#LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE    := hello    //生成的so文件名LOCAL_SRC_FILES := hello.c  //目标文件include $(BUILD_SHARED_LIBRARY)

Appliction.mk 指定编译的平台

APP_ABI := all

意思是编译全部的平台

5.编译so

在Android项目的目录下执行ndk-build

不出错so文件就生成了。

调用：

public class MainActivity extends Activity {public static native String getStringFromC();private TextView mTextView;static {// 调用库文件System.loadLibrary("hello");}@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mTextView = (TextView) findViewById(R.id.textview1);// 调用方法mTextView.setText(getStringFromC());}}