注意OpenCV 4.0.1 解决了这个问题请直接下载OpenCV 4.0.1

但是OpenCV 4.0.1作为模块导入Android Studio会有找不到R.styleable的问题

OpenCV 4.0.1 找不到R.styleable解决

 

 

 

 

 

 

 

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 static library####################
#first step to use opencv
set(OpenCV_STATIC ON)
#second step to use opencv
set(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 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

        #foutth step to use opencv link opencv
        ${OpenCV_LIBS}
        # Links the target library to the log library
        # included in the 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 <jni.h>
#include <string>
#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.
Error while executing process C:\sdk\cmake\3.6.4111459\bin\cmake.exe with arguments {--build C:\sdk\demo\usePrebuiltStaticLibrary\app\.externalNativeBuild\cmake\debug\armeabi-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 ..\..\..\..\build\intermediates\cmake\debug\obj\armeabi-v7a\libnative-lib.so
FAILED: cmd.exe /C "cd . && C:\sdk\ndk-bundle\toolchains\llvm\prebuilt\windows-x86_64\bin\clang++.exe  --target=armv7-none-lin