首先打开project structure确认你的Gradle version和Android Plugin Version版本。你的版本只能比这个高，我的版本如下。

图片.png

接下来按照一般jni开发流程走

创建native方法：

public class OpenCVNativeClass {
    static {
        System.loadLibrary("MyLibs");
    }
    public  static  native int Convert2Gray(long matAddrRgba,long matAddrGray);
}

生成头文件。我这里直接写了cpp文件(src\main\jni\xxx.cpp)

//
// Created by lx on 2017/3/21.
//
#include <jni.h>
#include <opencv2/opencv.hpp>
extern "C" {//我在这里被坑了，切记c++文件中在这里要写这个关键字
using namespace cv;
using namespace std;
int toGray(Mat img,Mat &gray);
JNIEXPORT jint JNICALL Java_erg_mylibrary_OpenCVNativeClass_Convert2Gray
  (JNIEnv * env, jclass obj, jlong addrRgba, jlong addrGray){
    Mat & mRgb = *(Mat *)addrRgba;
    Mat & mGray = * (Mat *)addrGray;
    int conv;
    jint retVal;
    conv = toGray(mRgb,mGray);
    retVal = (jint)conv;
    return retVal;
  }
      int toGray(Mat img,Mat& gray){
      cvtColor(img,gray,CV_RGBA2GRAY);
      if(gray.rows==img.rows && gray.cols == img.cols){
      return 1;
      }
      return 0;
      }
}

编写Android.mk文件

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

#opencv
OPENCV_CAMERA_MODULES:=on
OPENCV_INSTALL_MODULES:=on
OPENCV_LIB_TYPE:=SHARED
#修改为你自己的路径
include C:\Users\lx\Desktop\OpenCV-android-sdk\sdk\native\jni\OpenCV.mk


#your code
LOCAL_SRC_FILES:=erg_mylibrary_OpenCVNativeClass.cpp
LOCAL_LDLIBS += -llog
LOCAL_MODULE := MyLibs

include $(BUILD_SHARED_LIBRARY)

Application.mk

APP_STL := gnustl_shared
APP_CPPFLAGS := -frtti -fexceptions -std=c++11
#这里编译平台选择app支持的最小sdk
APP_PLATFORM := android-15
APP_ABI := armeabi armeabi-v7a

配置gradle

 externalNativeBuild {
        ndkBuild {
            path 'src/main/jni/Android.mk'
        }
    }

此时Sync Project，然后make project。Make成功后可以在build\intermediates\ndk-build\debug\下考到生成的so文件。

图片.png

Ok！到这里JNI完成。可以的java中调用了。（在之前的例子上修改）

public class OpenCVNativeClass {
    static {
        System.loadLibrary("MyLibs");
    }
    public  static  native int Convert2Gray(long matAddrRgba,long matAddrGray);
}

package erg.mylibrary;

import android.app.Activity;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.util.Log;
import android.view.SurfaceView;

import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.CameraBridgeViewBase;
import org.opencv.android.InstallCallbackInterface;
import org.opencv.android.JavaCameraView;
import org.opencv.android.LoaderCallbackInterface;
import org.opencv.android.OpenCVLoader;
import org.opencv.core.CvType;
import org.opencv.core.Mat;

/**
 * Created by lx on 2017/3/21.
 */

public class MainActivity extends Activity implements  CameraBridgeViewBase.CvCameraViewListener2  {
    static String TAG = "MainActivity";
    private JavaCameraView JavaCameraView;

//彩色 黑白Mat
    private  Mat mRgb,Gray;

    LoaderCallbackInterface LoaderCallbackInterface = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            switch (status) {
                case org.opencv.android.LoaderCallbackInterface.SUCCESS:
                    JavaCameraView.enableView();
                    break;
                default: {
                    super.onManagerConnected(status);
                }
            }
        }

        @Override
        public void onPackageInstall(int operation, InstallCallbackInterface callback) {

        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        JavaCameraView = (org.opencv.android.JavaCameraView) findViewById(R.id.CameraView);
        JavaCameraView.setVisibility(SurfaceView.VISIBLE);
        JavaCameraView.setCvCameraViewListener(this);
    }

    @Override
    public void onCameraViewStarted(int width, int height) {
        mRgb = new Mat(height, width, CvType.CV_8UC4);
        Gray = new Mat(height, width, CvType.CV_8UC4);
    }

    @Override
    public void onCameraViewStopped() {

        mRgb.release();
        Gray.release();
    }

    @Override
    public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
        mRgb = inputFrame.rgba();
      //JNI 图片处理,彩色图变为黑白图
OpenCVNativeClass.Convert2Gray(mRgb.getNativeObjAddr(),Gray.getNativeObjAddr());
        return Gray;
    }

    @Override
    protected void onStart() {
        super.onStart();
        if (OpenCVLoader.initDebug()) {
            Log.d(TAG, "Opencv Success");
            LoaderCallbackInterface.onManagerConnected(BaseLoaderCallback.SUCCESS);

        } else {
            Log.d(TAG, "Opencv fail");
            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_2_0, this, LoaderCallbackInterface);
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        JavaCameraView.disableView();

    }

    @Override
    protected void onResume() {
        super.onResume();
        JavaCameraView.enableView();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        JavaCameraView.disableView();

    }
}