首先下载NDK 然后在最外层的
local.properties文件夹中 写上 ndk的路径
ndk.dir=/Users/wyj/Desktop/androidStudioSdk/android-ndk-r10d
1.新建工程myapp
2.在MainActivity中写好
public static native String stringFromJNI();
2.生成对应的class文件
右键工程 Make Module ‘myapp’ 会生成 build文件夹 旗下很多 *.class
3.生成native对应的 .h 文件
命令格式
-classpath <路径> 用于装入类的路径
-d <目录> 输出目录
-jni 生成 JNI样式的头文件（默认）
注意MainActivity.class是个二进制文件，当前文件夹目录是myapp
终端下切换到myapp下 执行 要带上android.jar，因为 Activity中一些类需要android.jar中的类
mac下(:)
javah -classpath build/intermediates/classes/debug:/Users/wyj/Desktop/a/android.jar -d jni com.example.wyj.myapplication.MainActivity
windows下(;)
javah -classpath build\intermediates
\classes\debug;d:\Android\SDK\platforms\android-23\android.jar -d jni2 -jni com.
example.wyj.myapplication.MainActivity
其中Android.mk的内容是 其中：
LOCAL_MODULE := hello 生成的库名 生成 libhello.so
LOCAL_SRC_FILES := hello.c 指定哪个文件 都是.c文件
# 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
LOCAL_SRC_FILES := hello.c include $(BUILD_SHARED_LIBRARY)
com_example_wyj_myapplication_MainActivity.h的内容如下
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_example_wyj_myapplication_MainActivity */ #ifndef _Included_com_example_wyj_myapplication_MainActivity
#define _Included_com_example_wyj_myapplication_MainActivity
#ifdef __cplusplus
extern "C" {
#endif
#undef com_example_wyj_myapplication_MainActivity_BIND_ABOVE_CLIENT
#define com_example_wyj_myapplication_MainActivity_BIND_ABOVE_CLIENT 8L
#undef com_example_wyj_myapplication_MainActivity_BIND_ADJUST_WITH_ACTIVITY
#define com_example_wyj_myapplication_MainActivity_BIND_ADJUST_WITH_ACTIVITY 128L
#undef com_example_wyj_myapplication_MainActivity_BIND_ALLOW_OOM_MANAGEMENT
#define com_example_wyj_myapplication_MainActivity_BIND_ALLOW_OOM_MANAGEMENT 16L
#undef com_example_wyj_myapplication_MainActivity_BIND_AUTO_CREATE
#define com_example_wyj_myapplication_MainActivity_BIND_AUTO_CREATE 1L
#undef com_example_wyj_myapplication_MainActivity_BIND_DEBUG_UNBIND
#define com_example_wyj_myapplication_MainActivity_BIND_DEBUG_UNBIND 2L
#undef com_example_wyj_myapplication_MainActivity_BIND_IMPORTANT
#define com_example_wyj_myapplication_MainActivity_BIND_IMPORTANT 64L
#undef com_example_wyj_myapplication_MainActivity_BIND_NOT_FOREGROUND
#define com_example_wyj_myapplication_MainActivity_BIND_NOT_FOREGROUND 4L
#undef com_example_wyj_myapplication_MainActivity_BIND_WAIVE_PRIORITY
#define com_example_wyj_myapplication_MainActivity_BIND_WAIVE_PRIORITY 32L
#undef com_example_wyj_myapplication_MainActivity_CONTEXT_IGNORE_SECURITY
#define com_example_wyj_myapplication_MainActivity_CONTEXT_IGNORE_SECURITY 2L
#undef com_example_wyj_myapplication_MainActivity_CONTEXT_INCLUDE_CODE
#define com_example_wyj_myapplication_MainActivity_CONTEXT_INCLUDE_CODE 1L
#undef com_example_wyj_myapplication_MainActivity_CONTEXT_RESTRICTED
#define com_example_wyj_myapplication_MainActivity_CONTEXT_RESTRICTED 4L
#undef com_example_wyj_myapplication_MainActivity_MODE_APPEND
#define com_example_wyj_myapplication_MainActivity_MODE_APPEND 32768L
#undef com_example_wyj_myapplication_MainActivity_MODE_ENABLE_WRITE_AHEAD_LOGGING
#define com_example_wyj_myapplication_MainActivity_MODE_ENABLE_WRITE_AHEAD_LOGGING 8L
#undef com_example_wyj_myapplication_MainActivity_MODE_MULTI_PROCESS
#define com_example_wyj_myapplication_MainActivity_MODE_MULTI_PROCESS 4L
#undef com_example_wyj_myapplication_MainActivity_MODE_PRIVATE
#define com_example_wyj_myapplication_MainActivity_MODE_PRIVATE 0L
#undef com_example_wyj_myapplication_MainActivity_MODE_WORLD_READABLE
#define com_example_wyj_myapplication_MainActivity_MODE_WORLD_READABLE 1L
#undef com_example_wyj_myapplication_MainActivity_MODE_WORLD_WRITEABLE
#define com_example_wyj_myapplication_MainActivity_MODE_WORLD_WRITEABLE 2L
#undef com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_DIALER
#define com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_DIALER 1L
#undef com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_DISABLE
#define com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_DISABLE 0L
#undef com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_SEARCH_GLOBAL
#define com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_SEARCH_GLOBAL 4L
#undef com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_SEARCH_LOCAL
#define com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_SEARCH_LOCAL 3L
#undef com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_SHORTCUT
#define com_example_wyj_myapplication_MainActivity_DEFAULT_KEYS_SHORTCUT 2L
#undef com_example_wyj_myapplication_MainActivity_RESULT_CANCELED
#define com_example_wyj_myapplication_MainActivity_RESULT_CANCELED 0L
#undef com_example_wyj_myapplication_MainActivity_RESULT_FIRST_USER
#define com_example_wyj_myapplication_MainActivity_RESULT_FIRST_USER 1L
#undef com_example_wyj_myapplication_MainActivity_RESULT_OK
#define com_example_wyj_myapplication_MainActivity_RESULT_OK -1L
/*
* Class: com_example_wyj_myapplication_MainActivity
* Method: stringFromJNI
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_com_example_wyj_myapplication_MainActivity_stringFromJNI
(JNIEnv *, jclass); #ifdef __cplusplus
}
#endif
#endif
自己创建个 hello.c
#include <stdio.h>
#include <string.h>
#include "com_example_wyj_myapplication_MainActivity.h" JNIEXPORT jstring JNICALL Java_com_example_wyj_myapplication_MainActivity_stringFromJNI
(JNIEnv *env, jclass jclass){
return (*env)->NewStringUTF(env, "Hello from wf! ");
}
4.生成 so文件
终端在jni的上一级目录中 执行 ndk-build (ndk-build所在路径中的文件夹不得存在空格否则就报错了)
5.使用 so文件
在main中建立 jniLibs文件夹 然后把 armeabi/*.so 拷贝进去 然后就可以访问了。
或者不新建jniLibs文件夹，那么在build.gradle中
android {
sourceSets {
main {
jniLibs.srcDirs = ['xxx']
}
}
}
jniLibs.srcDirs = [‘xxx’] //这里xxx代表一个目录。可以改变jniLibs的读取路径 ， 默认的 jniLibs结构是 src/main/jniLibs
指定xxx是libs就可以了armeabi不需要在路径中指定，它是不同设备下的自动会被寻找的。
6.在MainActivity中 写上
public static native String stringFromJNI();
static {
System.loadLibrary("hello"); //装载库文件
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
String str=stringFromJNI(); //可被使用
System.out.print(str);
}
7.运行程序就可以 stringFromJNI 就可以看出结果了
额外说明：
.c文件中的函数为
1 JNIEXPORT jstring JNICALL Java_com_example_wyj_myapplication_MainActivity_stringFromJNI
类的结构 是 com.example.wyj.myapplication 文件包结构的 MainActivity类 下面的 stringFromJNI 函数才能被识别并使用
放入其它工程如果不是遵从这个结构的 会报错，函数找不到，当然*.so可以加载。
如果其他工程是遵守如下结构的当然也能识别出stringFromJNI函数并使用
