Android studio 使用Cmake完成C/C++ 的使用以及生成so文件

今天，简单讲讲android中关于Cmake进行NDK编程的相关知识。

Android studio 2.2版本以后对C/C++的支持可以说很方便了，当然官方推荐使用Cmake完成对C/C++的支持

2.2版本以上的同学新建一个项目就知道了，步骤如下：

File -> New -> New Project,如下图：

然后勾选Include C++ support,一直next ，最后Finish以后，项目就出现了，和一般的项目略有不同，其实只要多了几个文件，而已：

1：目录下多了个CmakeLists.txt文件

2：src目录下多了一个cpp目录，里面有个.cpp文件，C++文件都是以.cpp结尾的。

3：就是build.gradle内容中添加了几行配置

一一解读一下，先来看看CmakeLists.txt 文件里面的内容是什么：

# 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             # Sets the library as a shared library.             SHARED             # Provides a relative path to your source file(s).             src/main/cpp/native-lib.cpp )# 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.                       native-lib                       # Links the target library to the log library                       # included in the NDK.                       ${log-lib} )

这里有设置Cmake版本啊，引用的cpp文件的路径啊等等，如果自己引用的话 其实值需要修改引用的cpp路径即可，

其他的暂时不需要动

看下native_lib.cpp文件内容：

#include <jni.h>#include <string>extern "C"JNIEXPORT jstring JNICALLJava_com_process_main_myapplication_MainActivity_stringFromJNI(        JNIEnv* env,        jobject /* this */) {    std::string hello = "Hello from C++";    return env->NewStringUTF(hello.c_str());}

很简单 其实就是输出Hello from C++这段文字：

再看下build.gradle的配置改变：

apply plugin: 'com.android.application'android {    compileSdkVersion 25    buildToolsVersion "25.0.2"    defaultConfig {        applicationId "com.process.main.myapplication"        minSdkVersion 22        targetSdkVersion 25        versionCode 1        versionName "1.0"        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"        externalNativeBuild {            cmake {                cppFlags ""            }        }    }    buildTypes {        release {            minifyEnabled false            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'        }    }    externalNativeBuild {        cmake {            path "CMakeLists.txt"        }    }}dependencies {    compile fileTree(dir: 'libs', include: ['*.jar'])    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {        exclude group: 'com.android.support', module: 'support-annotations'    })    compile 'com.android.support:appcompat-v7:25.1.1'    compile 'com.android.support.constraint:constraint-layout:1.0.0-beta4'    testCompile 'junit:junit:4.12'}

主要多了两个地方的改变：

1：defaultConfig中添加：

externalNativeBuild {            cmake {                cppFlags ""            }        }

2：在android{}中添加：

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

其实也就是引用CmakeLists.txt文件。

现在重点讲讲CmakeLists.txt里面的代码的含义。

以上的CmakeLists.txt对于与图片的目录结构，可以看出主要是add_liberary里写入需要编译的C文件的路径，其余的基本不用修改。

还有就是要是在add_liberary中添加.cpp文件的话记得路径，如果你的CMakeLists和你的.cpp在一个问价夹下就不用管路径。

Android studio 使用Cmake完成C/C++ 的使用以及生成so文件就讲完了。

就这么简单。