Android Studio 2.2 在已有项目中添加NDK

1、加载库与编写native方法

2、在Terminal命令窗口下进入到java文件夹，执行如下命令：javah  包名.类名，生成头文件。

3、在项目的main文件夹下新建一个cpp文件夹，然后新建一个cpp文件，这个文件名要与代码System.loadLibrary("patch")中的参数名称相同。在这里我把文件名定为patch

4、把在第二步中生成的头文件中的方法复制到，patch.cpp中。在头文件中的方法名如下：

     JNIEXPORT jstring JNICALL Java_com_example_eric_filepatch_MainActivity_getStringFromNative(JNIEnv *, jobject);

    以上的写法在调用的时候出现问题，我把它改成以下的写法

    extern "C" jstring Java_com_example_eric_filepatch_MainActivity_getStringFromNative(JNIEnv *env, jobject);

    这样就可以正常使用了。

     其中extern “C” 是表示当代码使用C与C++混编时，指示编译器按照C语言进行编译。在extern “C” 中include进去的文件不能再有extern “C”， 因为extern “C”不能再有

     extern “C”。

    当include文件时，相当于把代码拷贝了一份放到该文件中

5、在local.properties文件下添加如下代码：

      ndk.dir=D\:\\Android\\android_sdk\\android_sdk\\ndk-bundle

6、在app文件夹下新建一个CMakeLists.txt文件，内容如下

    

    

# Sets the minimum version of CMake required to build the native
# library. You should either keep the default value or only pass a
# value of 3.4.0 or lower.

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 it for you.
# Gradle automatically packages shared libraries with your APK.

add_library( # Sets the name of the library.
             patch

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             # Associated headers in the same location as their source
             # file are automatically included.
             src/main/cpp/patch.cpp )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because system libraries are included 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

              # 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 the
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
                       patch

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

    其中带有#号的代码是注释，说明如下

   # 指定cmake最低版本，如果不知道就复制吧
   cmake_minimum_required(VERSION 3.4.1)

   # 第一个native-lib是供java调用的文件， SHARED是啥没看明白但是要写上
   # 最后是所有cpp的名字，这里在一个文件夹中就直接写名字了，文件有多少写多少，假如有 patch.cpp和 Max.cpp，记得写上路径
  add_library(patch SHARED src/main/cpp/patch.cpp src/main/cpp/Max.cpp)

  # 我的理解是java要连接到patch，和一些其它的东西，不懂
  target_link_libraries(patch)

7、在app的build.gradle中添加如下代码

  

     

    8、生成so文件

          首先在CMakeLists文件中添加如下的代码：

          set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../jniLibs/${ANDROID_ABI})

          该行代码的作用是把生成的so文件输出到指定的目录，在这里是输出到jniLibs文件夹下，改行代码的位置要在以下代码的下面

          cmake_minimum_required(VERSION 3.4.1)

          然后再build.gradle中添加需要输出的so文件类型，如下图所示。

1

   

然后就可以运行了。当然还有另外一种在原有的项目中添加NDK开发的方式，使用的是android.mk文件。在这里就不介绍了。

参考：http://blog.csdn.net/lmw21848/article/details/52183584

CMake:http://www.hahack.com/codes/cmake/