今天介绍一下Android Studio 2.2 下 NDK开发 ，那叫一个顺溜----纵享丝滑! 虽然现在AS 2.2 之后，jni开发配置相当方便，但是还是建议大家从我的第一篇文章看起，从基础知识入手，并且要了解之前是如何配置NDK工程的，这是一个循序渐进的过程。
今天主要介绍一下如何分别在新工程和老工程中创建最新NDK项目。 #新工程创建Ndk Project ##创建
创建时候勾选 include C++ support。
在AS 2.2 之后，当我们创建工程的时候会在下面多出一个勾选框，是否支持C++，这里我们勾选，然后一路next。
然后最后一步我们会看到如下界面：
这里不一定所有的同学都能跑起来，是因为我在之前的博客 http://blog.csdn.net/github_33304260/article/details/62891083 里面配置过NDK，这里就不相信讲解了，大家可以参考之前的文章，如果有问题可以留言。
好啦，就这么简单创建成功啦，已经可以运行啦，我们跑起来看一下。
就是这么纵享丝滑，不过很多童鞋对于新的结构可能不熟悉 那么接下来就行详细讲解一下新的结构和文件。
##项目一览 ###1.目录结构 勾选了include C++ support 就会多出以下几个目录及文件。
.externalNativeBuild —> cmake 编译好的文件, 显示支持的各种硬件等信息 存放 .so 文件等Cmake相关文件cpp —> 众所周知 JNI Folder 。C 语言程序的逻辑部分, native-lib.cpp 文件名可自行修改CMakeLists.txt —> CMake 脚本配置的文件, 具体可查阅 CMake官网的资料###2.build.gradle中的Cmake
externalNativeBuild { cmake { cppFlags "" } } externalNativeBuild { cmake { path "CMakeLists.txt" } }Tips: 在Gradle里面多了以上两部分内容。当然这里默认的配置信息比较少，配置配置指令具体可查阅 CMake 官网。
###3.CMakeLists.txt文件中的具体配置
# For more information about using CMake with Android Studio, read the # documentation: https://d.android.com/studio/projects/add-native-code.html # Sets the minimum version of CMake required to build the native library. cmake_minimum_required(VERSION 3.4.1) # Creates and names a library, sets it as either STATIC # or SHARED, and provides the relative paths to its source code. # You can define multiple libraries, and CMake builds them for you. # Gradle automatically packages shared libraries with your APK. add_library( # Sets the name of the library. native-lib # 这个是jni编译生产的so库的名字 # Sets the library as a shared library. SHARED # Provides a relative path to your source file(s). src/main/cpp/native-lib.cpp ) # 要编译的c/c++文件列表 文件路径想对于cmake文件路径 # Searches for a specified prebuilt library and stores the path as a # variable. Because CMake includes system libraries in the search path by # default, you only need to specify the name of the public NDK library # you want to add. CMake verifies that the library exists before # completing its build. find_library( # Sets the name of the path variable. log-lib # 依赖的系统so库 # Specifies the name of the NDK library that # you want CMake to locate. log ) # Specifies libraries CMake should link to your target library. You # can link multiple libraries, such as libraries you define in this # build script, prebuilt third-party libraries, or system libraries. target_link_libraries( # Specifies the target library. native-lib # Links the target library to the log library # included in the NDK. ${log-lib} )###4·MainAvtivity中新增的方法 1、在java代码中增加引用so库的代码,使代码生效
// Used to load the 'native-lib' library on application startup. static { //此处的form库的名称需要和CMakeLists.txt中配置的相同 System.loadLibrary("native-lib"); }2、定义方法
/** * A native method that is implemented by the 'native-lib' native library, * which is packaged with this application. */ public native String stringFromJNI();###5· native-lib.cpp 里面可以直接的创建cpp源代码,和ndkBuild一样,用C/C++所写的源代码中的方法名称必须是全路径的方法名,然后以Java开头,分割使用下划线.
#include <jni.h> #include <string> extern "C" JNIEXPORT jstring JNICALL Java_pressure_libin_com_pressure_MainActivity_stringFromJNI( JNIEnv *env, jobject /* this */) { std::string hello = "Hello from C++"; return env->NewStringUTF(hello.c_str()); }extern "C" ： 暴露给外部使用。 确保所有Java需要调用的C方法都放在extern "C"中，这样CMake才会帮我们正确编译。
好啦 到这里 新鲜东西就已经都讲完了。 接下来看看如何在旧工程中添加最新NDK Project。
#老工程导入Ndk Project
1 选择app—> 右键 New —> Folder —> JNI Folder 。
选中 Change Folder Location 将JNI更换成cpp （为了统一 ，系统自动生成的是cpp文件 CMakeLists.txt里面配置也是cpp路径 ）
cpp文件夹 这个文件夹颜色和java一样 说明你创建对了。
2 选择 jni —> New —> C/C++Source File
3 完善native-lib.cpp文件
#include <jni.h> #include <string> extern "C" }4 在APP目录下添加 CMakeLists.txt 文件
代码和上面创建后生成的一样，具体功能自行添加。 切记： jni编译生产的so库的名字和路径要正确
# For more information about using CMake with Android Studio, read the # documentation: https://d.android.com/studio/projects/add-native-code.html # Sets the minimum version of CMake required to build the native library. cmake_minimum_required(VERSION 3.4.1) # Creates and names a library, sets it as either STATIC # or SHARED, and provides the relative paths to its source code. # You can define multiple libraries, and CMake builds them for you. # Gradle automatically packages shared libraries with your APK. add_library( # Sets the name of the library. native-lib # 这个是jni编译生产的so库的名字 # Sets the library as a shared library. SHARED # Provides a relative path to your source file(s). src/main/cpp/native-lib.cpp ) # 要编译的c/c++文件列表 文件路径想对于cmake文件路径 # Searches for a specified prebuilt library and stores the path as a # variable. Because CMake includes system libraries in the search path by # default, you only need to specify the name of the public NDK library # you want to add. CMake verifies that the library exists before # completing its build. find_library( # Sets the name of the path variable. log-lib # 依赖的系统so库 # Specifies the name of the NDK library that # you want CMake to locate. log ) # Specifies libraries CMake should link to your target library. You # can link multiple libraries, such as libraries you define in this # build script, prebuilt third-party libraries, or system libraries. target_link_libraries( # Specifies the target library. native-lib # Links the target library to the log library # included in the NDK. ${log-lib} )5 make Project
6 关联CMakeLists.txt app — > Link C++ Project with Gradle
再次查看Gradle 发现 多了如下代码：
externalNativeBuild { cmake { path 'CMakeLists.txt' } }或者手动在Gradle添加上面代码。
7 引用so库
在MainActivity中引用：
public class MainActivity extends AppCompatActivity { //引用so库 static { System.loadLibrary("native-lib"); } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } }8 编写第一个jni方法
public native String stringFromJNI(); extern "C" JNIEXPORT jstring JNICALL Java_pressure_libin_com_pressure_MainActivity_stringFromJNI( JNIEnv *env, jobject /* this */) { std::string hello = "Hello from C++"; return env->NewStringUTF(hello.c_str()); }#NDK工程下Debug debug是一个非常重要的功能，在2.2之后，我们直接就可以对native代码进行debug。
在edit中可以对debug模式进行设置：
如图：
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