OpenCV4Android支持三种使用方式
1.Java层调用
2.NDK调用动态库(方便，但是会包含整个.so库)
3.NDK调用静态库(灵活，比如没有用到机器学习模块，libopencv_ml.a里的代码是不会打包到动态库里的)
通过链接静态库的方式使用OpenCV4Android，CMAKE配置如下
#############################prepare for using of opencv staticlibrary####################
#first step to use opencvset(OpenCV_STATIC ON)
#second step to use opencvset(OpenCV_DIR C:/sdk/opencv-3.4.2-android-sdk/sdk/native/jni)
#third step to use opencv
find_package(OpenCV REQUIRED)
###########################################################################################
##################################################the native-lib shared library############
# Creates and names a library, sets itaseither STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds themforyou.
# Gradle automatically packages shared libraries with your APK.
add_library( # Sets the name of the library.
native-lib
# Sets the libraryasa shared library.
SHARED
# Provides a relative path to your source file(s).
src/main/cpp/native-lib.cpp)
# Searchesfor a specified prebuilt library and stores the path asa
# variable. Because CMake includes system librariesinthe search path by
#default, you only need to specify the name of the publicNDK 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, suchas libraries you define in this# build script, prebuilt third-party libraries, or system libraries.
target_link_libraries( # Specifies the target library.
native-lib
#foutth step to use opencv link opencv
${OpenCV_LIBS}
# Links the target library to the log library
# includedinthe NDK.
${log-lib})
######################################################################################
仅仅是新建项目稍稍修改了native-lib.cpp的代码，在函数里用了下opencv的函数
#include #include#include"opencv2/core/core.hpp"#include"opencv2/imgproc/imgproc_c.h"
extern "C"JNIEXPORT jstring JNICALL
Java_com_example_useprebuiltstaticlibrary_MainActivity_stringFromJNI(
JNIEnv*env,
jobject/*this*/) {
std::string hello="hello";
cv::Mat m=cv::Mat::eye(3,3,CV_8UC1);return env->NewStringUTF(hello.c_str());
}
编译时却报错
Build command failed.
Errorwhile executing process C:sdkcmake3.6.4111459incmake.exe with arguments {--build C:sdkdemousePrebuiltStaticLibraryapp.externalNativeBuildcmakedebugarmeabi-v7a --target native-lib}
[1/2] Building CXX object CMakeFiles/native-lib.dir/src/main/cpp/native-lib.cpp.o
[2/2] Linking CXX shared library ........uildintermediatescmakedebugobjarmeabi-v7alibnative-lib.so
FAILED: cmd.exe/C "cd . && C:sdk
dk-bundleoolchainsllvmprebuiltwindows-x86_64inclang++.exe --target=armv7-none-linux-androideabi23 --gcc-toolchain=C:/sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/windows-x86_64 --sysroot=C:/sdk/ndk-bundle/sysroot -fPIC -isystem C:/sdk/ndk-bundle/sysroot/usr/include/arm-linux-androideabi -g -DANDROID -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -mthumb -mfpu=neon -Wa,--noexecstack -Wformat -Werror=format-security -std=c++11 -std=c++11 -O0 -fno-limit-debug-info -Wl,--exclude-libs,libgcc.a -Wl,--exclude-libs,libatomic.a -nostdlib++ --sysroot C:/sdk/ndk-bundle/platforms/android-23/arch-arm -Wl,--build-id -Wl,--warn-shared-textrel -Wl,--fatal-warnings -Wl,--fix-cortex-a8 -Wl,--exclude-libs,libunwind.a -LC:/sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a -Wl,--no-undefined -Wl,-z,noexecstack -Qunused-arguments -Wl,-z,relro -Wl,-z,now -shared -Wl,-soname,libnative-lib.so -o ........uildintermediatescmakedebugobjarmeabi-v7alibnative-lib.so CMakeFiles/native-lib.dir/src/main/cpp/native-lib.cpp.o C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_highgui.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_features2d.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_shape.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_imgcodecs.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_ml.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_videoio.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_dnn.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_flann.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_objdetect.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_calib3d.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_video.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_superres.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_photo.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_imgproc.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_stitching.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_videostab.a -llog C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/liblibprotobuf.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_calib3d.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_features2d.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_highgui.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_videoio.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_imgcodecs.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/liblibjpeg-turbo.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/liblibwebp.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/liblibpng.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/liblibtiff.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/liblibjasper.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/libIlmImf.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_flann.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_video.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_photo.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_imgproc.a C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a -lz C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/libtbb.a -lc C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/libcpufeatures.a -ldl -lm -llog C:/sdk/opencv-3.4.2-android-sdk/sdk/native/3rdparty/libs/armeabi-v7a/libtegra_hal.a -latomic -lm"C:/sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++_static.a" "C:/sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++abi.a" "C:/sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libunwind.a" "-ldl"&& cd ."C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function std::basic_ostream >& std::operator<< <:char_traits> >(std::basic_ostream >&, char const*) [clone .part.13]: error: undefined reference to ‘std::basic_ios >::clear(std::_Ios_Iostate)‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function cv::Exception::formatMessage(): error: undefined reference to ‘std::basic_stringstream, std::allocator >::basic_stringstream(std::_Ios_Openmode)‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function cv::Exception::formatMessage(): error: undefined reference to ‘std::basic_ostream >& std::__ostream_insert >(std::basic_ostream >&, char const*, int)‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function cv::Exception::formatMessage(): error: undefined reference to ‘std::basic_ostream >& std::__ostream_insert >(std::basic_ostream >&, char const*, int)‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function cv::Exception::formatMessage(): error: undefined reference to ‘std::ostream::put(char)‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function cv::Exception::formatMessage(): error: undefined reference to ‘std::ostream::flush()‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function cv::Exception::formatMessage(): error: undefined reference to ‘std::basic_ostream >& std::__ostream_insert >(std::basic_ostream >&, char const*, int)‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function cv::Exception::formatMessage(): error: undefined reference to ‘std::basic_ostream >& std::__ostream_insert >(std::basic_ostream >&, char const*, int)‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(system.cpp.o):system.cpp:function cv::Exception::formatMessage(): error: undefined reference to ‘std::ostream::put(char)‘.
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.C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(persistence_json.cpp.o):persistence_json.cpp:function icvJSONParseValue(CvFileStorage*, char*, CvFileNode*): error: undefined reference to ‘std::string::at(unsigned int)‘C:/sdk/opencv-3.4.2-android-sdk/sdk/native/staticlibs/armeabi-v7a/libopencv_core.a(persistence.cpp.o):persistence.cpp:function check_if_write_struct_is_delayed(CvFileStorage*, bool): error: undefined reference to ‘std::string::assign(char const*, unsigned int)‘clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
google得知是因为编译这些静态库时所用的编译器、标准库等跟NDK当前的版本不同。网上的建议都是stl改为gnustl_static或gnustl_shared之类。可较新的NDK都不支持这些stl了，为了使用OpenCV静态库只能重新编译了。
编译OpenCV4Android的过程里爬了不少坑，总结一下，希望有助于小白们。
1. 安装MinGW
这里不详细的说了，网上很多教程。选择如图三项安装
安装好后差不多二三百兆，在环境变量Path里添加
C:MinGWin
C:MinGWmsys1.0in
这里C:MinGW是我的安装目录。配置好后需要注销计算机，再登陆。在命令行里gcc -v看到能输出版本就算差不多设置好环境了。
2. CMAKE 配置
下载好源代码解压，我放在C:opencv-3.4.2。打开CMAKE图形界面
如图一定要选择MinGW Makefiles，我想这也是为什么一定要先安装配置MinGW的原因。选择指定工具链，点击next
这里一定要注意，选择的不是源代码
opencv-3.4.2platformsandroidandroid.toolchain.cmake
这个工具链，这个工具链过时了。新版本的NDK带有自己的工具链，这里选择NDK
/build/cmake/android.toolchain.cmake这个工具链。
这里感谢
https://github.com/opencv/opencv/issues/8742
点击Finish。有错误别管，点击configure。开始配置。出现错误就再点configure直到遇到一个跳不过去的错误，看看是不是让你配置SDK路径
Android SDK: specify path to Android SDK via ANDROID_SDK_ROOT /ANDROID_HOME/ ANDROID_SDK variables
点击Add Entry添加变量
注意类型是FilePath。点击OK。点击configure。很快又跳出一个错误
CMake Error at cmake/android/android_gradle_projects.cmake:1(message):
Android gradle-based build/projects are not supported in thisversion of
OpenCV.
You need to downgrade Android SDK Tools to version25.2.5.
Details: https://github.com/opencv/opencv/issues/8460
Call Stack (most recent call first):
cmake/android/OpenCVDetectAndroidSDK.cmake:204(include)
CMakeLists.txt:645 (include)
这是SDK比较新，新的SDK只支持Gradle编译，而OpenCV需要Ant编译。这里也给出了解决方法
Details: https://github.com/opencv/opencv/issues/8460
就是下载一个较旧的SDK。正如连接所说，windows选择这个
https://dl.google.com/android/repository/tools_r25.2.5-windows.zip
解压后发现里面只有一个tool目录，而SDK里也有一个tool目录。我的做法是先重命名SDK里的tool为tool28。再将下载的tool复制进SDK。
点击configure。(这里可能还是这个错误，这样就需要删除C:opencv-3.4.2uild里所有内容，重启CMAKE。再来一次。所以这一步最好在CMAKE前就做好。
接下来会遇到这个错误
CMake Error at cmake/android/OpenCVDetectAndroidSDK.cmake:184(message):
Android SDK: Can‘t build Android projects as requested by
BUILD_ANDROID_PROJECTS=ON variable.
Use BUILD_ANDROID_PROJECTS=OFF to prepare Android project files without
building them
Call Stack (most recent call first):
CMakeLists.txt:645 (include)
如图搜索这个变量，取消选择。点击configure。
配置成功。
如图搜做tbb选择两项，否则不生成libtbb.a库，我不知这又什么用，但是预编译的SDK里有这个。
还有其它的一些变量可以配置，比如添加ANDROID_ABI，否则仅仅生成armeabi-v7a。修改变量、添加变量后记得configure。
配置完成点击generate，生成完成。CMAKE可关闭了。
3.编译
命令行进入C:opencv-3.4.2uild目录，这里有很多配置好的文件，输入mingw32-make，就开始编译。等好久就成功了。
C:opencv-3.4.2uild>mingw32-make
Scanning dependencies of target gen-pkgconfig
[0%] Generate opencv.pc
[0%] Built target gen-pkgconfig
Scanning dependencies of target libcpufeatures
[0%] Building C object 3rdparty/cpufeatures/CMakeFiles/libcpufeatures.dir/cpu-features.c.o
[0%] Linking C static library ..libarmeabi-v7alibcpufeatures.a
[0%] Built target libcpufeatures
Scanning dependencies of target libjpeg-turbo
[0%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jcapimin.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jcapistd.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jccoefct.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jccolor.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jcdctmgr.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jchuff.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jcinit.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jcmainct.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jcmarker.c.o
[1%] Building C object 3rdparty/libjpeg-turbo/CMakeFiles/libjpeg-turbo.dir/src/jcmaster.c.o
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[99%] Linking CXX executable ....inopencv_perf_stitching
[99%] Built target opencv_perf_stitching
Scanning dependencies of target opencv_videostab
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/deblurring.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/fast_marching.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/frame_source.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/global_motion.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/inpainting.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/log.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/motion_stabilizing.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/optical_flow.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/outlier_rejection.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/stabilizer.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_videostab.dir/src/wobble_suppression.cpp.o
[100%] Linking CXX static library ....libarmeabi-v7alibopencv_videostab.a
[100%] Built target opencv_videostab
Scanning dependencies of target opencv_test_videostab
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_test_videostab.dir/test/test_main.cpp.o
[100%] Building CXX object modules/videostab/CMakeFiles/opencv_test_videostab.dir/test/test_motion_estimation.cpp.o
[100%] Linking CXX executable ....inopencv_test_videostab
[100%] Built target opencv_test_videostab
4.配置库
生成的库在
opencv-3.4.2uildlib
第三方库在
opencv-3.4.2uild3rdpartylib
将其复制到
opencv-3.4.2-android-sdk
相应目录下替换掉原来的
现在编译项目则没有链接错误了。
参考文章：
1.https://github.com/opencv/opencv/issues/8742
2.https://github.com/opencv/opencv/issues/8460
3.https://blog.youkuaiyun.com/xiao19950820/article/details/77119891
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