对于熟悉c++的人来说，如果能在android中写c++代码会是比较方便的，这时得用Cmake，配置并不复杂，甚至比ndk-build要简单，所以这一篇，就写用cmake导入opencv并在里面写一个例子的过程。我也是一边学一边摸索，一边踩坑一边记录经验，同时和大家分享交流一下。
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我的环境工具版本：
Android 3.0.1
OpenCV 3.4.1
创建工程
首先，创建项目工程的时候，勾选include c++ support
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一路next，到最后一步，如下：
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如果没有装CMake，建好以后会报错，那么安装Cmake
安装CMake
点击File—Settings—Appearance & Behavior – System Settings – Android SDK – SDK Tools,会看到Cmake选项，后面是Not Installed，说明没有安装CMake。勾选CMake，点击OK，联网情况下将会自动完成安装。
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将OpenCV下面的java文件夹导入项目中，File – New – Import Module 选择OpenCV-android-sdk\sdk\java导入，然后分别修改app和opencv的gradle中的版本号（详见前一篇）例如我的手机是android7.1.2的，所以SDK版本号全部设为了25。
在主模块中加入对OpenCV Library的依赖，File – Project structure –app –点右边“+”号，choose Module，选择opencvLibary341导入。
获得NDK/native的OpenCV支持。
具体来说：
把路径OpenCV-android-sdk\sdk\native\jni\include这个include文件夹整个拷到路径\app\src\main\cpp目录下
把路径为OpenCV-android-sdk\sdk\native\libs里面的几个文件夹，拷贝到\src\main\jniLibs下面。
检查App的gradle文件
android {
compileSdkVersion 25 defaultConfig { applicationId "scr.face_detection4" minSdkVersion 25 targetSdkVersion 25 versionCode 1 versionName "1.0" testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner" externalNativeBuild {
cmake {
cppFlags "-frtti -fexceptions" }
}
ndk{
abiFilters 'armeabi-v7a' } sourceSets.main{ jniLibs.srcDir 'src/main/jniLibs' // set .so files directory to libs jni.srcDirs = [] //disable automatic ndk-build call }
}
buildTypes {
release { minifyEnabled false proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro' }
}
externalNativeBuild {
cmake { path "CMakeLists.txt" }
}
}修改CmakeLists.txt
我的代码如下：
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.set(OpenCV_DIR D:/AndroidSDK/OpenCV-android-sdk/sdk/native/jni)
find_package(OpenCV REQUIRED)if(OpenCV_FOUND)
include_directories(${OpenCV_INCLUDE_DIRS})
message(STATUS "OpenCV library status:")
message(STATUS " version: ${OpenCV_VERSION}")
message(STATUS " libraries: ${OpenCV_LIBS}")
message(STATUS " include path: ${OpenCV_INCLUDE_DIRS}")else(OpenCV_FOUND)
message(FATAL_ERROR "OpenCV library not found")
endif(OpenCV_FOUND)set(CMAKE_VERBOSE_MAKEFILE on)set(libs "${CMAKE_SOURCE_DIR}/src/main/jniLibs")
include_directories(${CMAKE_SOURCE_DIR}/src/main/cpp/include)
add_library(libopencv_java3 SHARED IMPORTED )
set_target_properties(libopencv_java3 PROPERTIES
IMPORTED_LOCATION "${libs}/${ANDROID_ABI}/libopencv_java3.so")
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}
${OpenCV_LIBS}
-ljnigraphics
libopencv_java3
)去除OpenCV Manager 依赖
检查\src\main\jniLibs下面对应的发布平台的文件夹里是否有libopencv_java3.so文件，没有的话去OpenCV-android-sdk\sdk\native\libs里面拷一个
到MainActivity.java里面onCreate（）函数前面加一句话
static {
System.loadLibrary("opencv_java3");
System.loadLibrary("native-lib");
}写个例子测试一下
调用相机，要修改几个文件
AndroidManifest.xml
在最外层里面加入：
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/><uses-permission android:name="android.permission.CAMERA"/><uses-feature android:name="android.hardware.camera" android:required="true"/><uses-feature android:name="android.hardware.camera.autofocus" android:required="true"/><uses-feature android:name="android.hardware.camera.front" android:required="true"/><uses-feature android:name="android.hardware.camera.front.autofocus" android:required="true"/>
编写native-lib.cpp
写了个简单测试，就做边缘Canny检测吧
jstring Java_scr_face_1detection4_MainActivity_stringFromJNI( JNIEnv *env, jobject /* this */) {
std::string hello = "Hello from C++ Again"; return env->NewStringUTF(hello.c_str());
}
void Java_scr_face_1detection4_MainActivity_nativeProcessFrame(JNIEnv *, jobject, jlong addrGray, jlong addrRgba) {
Mat &mGr = *(Mat *) addrGray;
Mat &mRgb = *(Mat *) addrRgba;
Canny(mGr,mRgb,50,200);
}回到MainActivity.java，调用native-lib
public class MainActivity extends AppCompatActivity implements CvCameraViewListener2{ private static final String TAG = "MainActivity"; private Mat mRgba; private Mat mIntermediateMat; private Mat mGray; private CameraBridgeViewBase mOpenCvCameraView; // Used to load the 'native-lib' library on application startup.
static {
System.loadLibrary("opencv_java3");
System.loadLibrary("native-lib");
} @Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON); // Example of a call to a native method
TextView tv = (TextView) findViewById(R.id.sample_text);
tv.setText(stringFromJNI()); //add
mOpenCvCameraView = (CameraBridgeViewBase) findViewById(R.id.tutorial2_activity_surface_view);
mOpenCvCameraView.setVisibility(CameraBridgeViewBase.VISIBLE);
mOpenCvCameraView.setCvCameraViewListener(this);
mOpenCvCameraView.setClickable(true);
} @Override
public void onPause()
{ super.onPause(); if (mOpenCvCameraView != null)
mOpenCvCameraView.disableView();
} @Override
public void onResume()
{ super.onResume(); if (!OpenCVLoader.initDebug()) {
Log.d(TAG, "Internal OpenCV library not found. Using OpenCV Manager for initialization");
} else {
Log.d(TAG, "OpenCV library found inside package. Using it!");
mOpenCvCameraView.enableView();
}
} public void onDestroy() { super.onDestroy(); if (mOpenCvCameraView != null)
mOpenCvCameraView.disableView();
} public void onCameraViewStarted(int width, int height) {
mRgba = new Mat(height, width, CvType.CV_8UC4);
mIntermediateMat = new Mat(height, width, CvType.CV_8UC4);
mGray = new Mat(height, width, CvType.CV_8UC1);
} public void onCameraViewStopped() {
mRgba.release();
mGray.release();
mIntermediateMat.release();
} public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
mRgba = inputFrame.rgba();
mGray = inputFrame.gray();
nativeProcessFrame(mGray.getNativeObjAddr(), mRgba.getNativeObjAddr()); return mRgba;
}/**
* A native method that is implemented by the 'native-lib' native library,
* which is packaged with this application.
*/
public native String stringFromJNI(); public native void nativeProcessFrame(long matAddrGr, long matAddrRgba);
}运行就可以了。这样就是通过CMake调用cpp里面的OpenCV代码了。
运行效果图.jpg
调试中出现过的问题
Execution failed for task ':app:externalNativeBuildDebug'.
这个问题是上文中CmakeLists.txt中的set后的路径没写对造成的，仔细检查修改后就过了。
This adb server's $ADB_VENDOR_KEYS is not set
真机调试的时候遇到过这个问题，因为自己对AS调试还不太了解，连接好了就解决了。连接分两部分，一方面是AS里面的设置，按下图调好
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作者：晚晴风_
链接：https://www.jianshu.com/p/439d8cc479bf
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