android开发 使用cmake构建jni工程，并添加opencv模块

向现有项目添加 C/C++ 代码

1.切换到project试图，在app下，打开build.gradle

在android{}中添加：

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

2.project>>app>>new>>file 创建CMakeLists.txt

cmake_minimum_required(VERSION 3.4.1)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
set(ProjectDir /home/cuizhou/codes/AndroidStudioProjects/CuiZhou-JNI-OpenCV-SSD-Mobilenet-Demo)

#-----------------------------------------------------
# wrapper

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)

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 )

target_link_libraries( # Specifies the target library.
native-lib

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

# lib_opencv)

3.编写java native 方法，并生成头文件

在MainActivity中添加native方法

static {
System.loadLibrary("native-lib");
}
public native String stringFromJNI();

或者新建类 MyClass.java, 生成头文件

cd project/app/src/main/java
javah -cp ~/Android/Sdk/platforms/android-27/android.jar:. com.example.MyClass

4.新建cpp,实现jni函数

添加opencv模块

从观望上下载android for opencv

把OpenCV-android-sdk/sdk/native/libs拷贝到src/main/目录下，重新命名为jniLibs

在CMakeList中添加

#-----------------------------------------------------
# OpenCV
set(pathToOpenCv /home/cuizhou/codes/AndroidStudioProjects/OpenCV3.4-android-sdk)
include_directories(${pathToOpenCv}/sdk/native/jni/include)
add_library(lib_opencv STATIC IMPORTED )
set_target_properties(lib_opencv
PROPERTIES
IMPORTED_LOCATION ${ProjectDir}/app/src/main/jniLibs/${ANDROID_ABI}/libopencv_java3.so
)

在native cpp中可以使用opencv

#include <opencv2/core/cvdef.h>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace cv;
...
cv::Mat srcImage=cv::Mat::zeros(cv::Size(300,300),CV_8UC1);
...

参考

官方文档，config cmake：

https://developer.android.com/studio/projects/configure-cmake.html#add-other-library

很好的翻译文档：

http://blog.csdn.net/check816/article/details/77074323

todo：

梳理《透析Android以JNI调OpenCV的三种方式》

http://blog.csdn.net/yanzi1225627/article/details/27863615

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