如何在AndroidStudio中使用cmake编译NDK

一、概述  

   之前由于AS没有强制，所以也就守旧一直沿用以前的NDK开发方法，在gradle.properties添加android.useDeprecatedNdk=true的属性。可是AS3.0以后被强制必须使用Cmake编译了，不得已才来学学，终于发现了这东东的好处。Cmake是AS在2.2中提出的更加方便的JNI开发的构建工具，相当于之前使用是NDK-BUILDE，。

Cmake的优势：作为一个java语言开发者，每次要接触C/C++的时候内心都是拒绝的，今天用了Cmake。终于发现写C++语言也可以轻而易举。居然带自动补全功能，而且所有步骤包括头文件生成，javac编译等等全部不需要你来弄，只需要编写完代码放入对应位置，然后编写配置CMakeLists.txt即可。

二、如何使用CMAKE

       1. 首先安装 Cmake 插件， File->setting-> 搜 SDK-> 找到 SDK Tools 如下。 选中图中的 Cmake 和 LLDB 插件（这个工具就是用来在 AS 中调试 native 代码的）

如果没有下插件的话会报如下错：Gradle sync failed: Unable to get the CMake version located at: C:\Users\suzhiming\AppData\Local\Android\Sdk\cmake\bin  Consult IDE log for more details (Help | Show Log) (936ms)

2. 在 module （ app ）的 build.gradle 中添加 

externalNativeBuild {
    cmake {
        cppFlags ""
    }
}

  如下图位置：在defauldConfig

3.接下来就是创建CMakeLists.txt文件。在app目录下，内容如下，注意标红的4个地方的修改

# 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.
             SerialPort 设置Lib库的名字，也就是你的C/C++类名

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/SerialPort.c ) 你的c/c++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

              # 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.
                       SerialPort 库名，就是java中调用system.Loadlibrary()的名字。 

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

 
4. 将 CMakeLists文件加到build.gradle参与编译

externalNativeBuild {
    cmake {
        path "CMakeLists.txt"
    }
}

  位置如下图

5.build项目，生成.externalNativeBuild文件。

   build成功后，会在app根目录下生成这个目录。说明OK，配置成功了。这时候我们进入c/c++文件编写就可以发现编写过程中，就跟写java代码一样会自动关联，自动提示了

附：

 

（JNI的方法名全部以规定都是Java开头，然后包名的点变为_，最后加类名加方法名,例如我这里的是Java_protocol_sdk_shbst_com_protocolsdk_SerialPort_open，参照为1.Java 2.包名protocol.sdk.shbst.com.protocolsdk， 3.类名SerialPort  4.方法名open  ）。