一、项目结构

1. 项目配置
   主要是里面cmake的配置，ndk配置，设置cMakeLists.txt

   
   image.png
2. 目录结构
   .cpp文件和它需要的.h文件都放在cpp文件夹下
   .cpp文件依赖的.so文件则放在jniLibs文件夹下，jniLibs文件夹在Gradle脚本中是默认存放.so文件的位置，如果你想改它则需要在build.gradle中指定它的位置，如下设置:

sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
}

build.gradle设置

apply plugin: 'com.android.application'

android {
    compileSdkVersion 26
    defaultConfig {
        applicationId "com.example.dell.dualcampreview"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
            }
        }

        ndk {
            abiFilters 'armeabi-v7a'
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:26.1.0'
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
}

二、CMakeLists.txt中的设置

整体都是系统自动生成 的，只看关键的几个地方

1. add_library()总共有三个
   第一个是根据.cpp文件编译.so，如果有include的头文件的话，在后面加上include_directories()
   第二个和第三个则是前面.cpp文件所需要的依赖的库文件，在后面需要加上set_target_properties()来它依赖的.so文件
2. 末尾的 target_link_libraries，把前面的引入的库名都写上即可

# 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.


#此处可以通过多加几个addlibrary来针对多个cpp文件来生成多个.so文件
#它的用法跟Android.mk里的定义差不多
#需要留意，编译出来的文件放在\build\intermediates\cmake中,但是不用自己复制了，它会自动复制到
#jniLibs文件夹下
add_library(
    jniSTDualCamPreview
    SHARED
    src/main/cpp/main.cpp
)
#include的文件夹
include_directories(jniSTDualCamPreview
                    ${CMAKE_SOURCE_DIR}/src/main/cpp/include)

#两个预编译好的库
add_library(STdisp  SHARED  IMPORTED)
set_target_properties(STdisp PROPERTIES IMPORTED_LOCATION
                      ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libSTdisp.so)
add_library(Stereoblur  SHARED  IMPORTED)
set_target_properties(Stereoblur PROPERTIES IMPORTED_LOCATION
                      ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libStereoblur.so)



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

三、遇到的一个异常情况

1.编译.cpp正常，但是build生成apk的时候出的异常

> More than one file was found with OS independent path 'lib/armeabi-v7a/libmainLib.so'

处理方式

其实是因为自己把编译.cpp生成的.so复制到了jniLibs下，但是cMakeList它其实会自己去编译和复制，并且自动放到jniLibs下，所以最后打包的时候就会报错More than one file