CameraActivity initial setup

activity_camera.xml

<?xml version="1.0" encoding="utf-8"?>
<ScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".CameraActivity">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

      // this is the camera!
        <org.opencv.android.JavaCameraView
            android:layout_height="300dp"
            android:layout_width="200dp"
            android:id="@+id/cam_view"
            android:layout_alignParentTop="true"
            />

    </RelativeLayout>
</ScrollView>

CameraActivity.java

package com.example.android.myapplication;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.SurfaceView;

import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.CameraBridgeViewBase;
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;

public class CameraActivity extends AppCompatActivity implements CameraBridgeViewBase.CvCameraViewListener {

    private static final String TAG = "CameraActivity";
    
    // Initialize OpenCVLoader
    static {
        if (!(OpenCVLoader.initDebug())) {
            Log.d(TAG, "  OpenCVLoader.initDebug(), working.");
        } else {
            Log.d(TAG, "  OpenCVLoader.initDebug(), not working.");
        }
    }

    JavaCameraView javaCameraView;
    Mat usedMat;

    // Override the BaseLoaderCallback-method from OpenCV, to manage initialization properly
    BaseLoaderCallback mLoaderCallBack = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            switch (status) {
                case BaseLoaderCallback.SUCCESS:
                    javaCameraView.enableView();
                    break;
                default:
                    super.onManagerConnected(status);
                    break;
            }
        }
    };
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        javaCameraView = findViewById(R.id.cam_view);
        javaCameraView.setVisibility(SurfaceView.VISIBLE);
        javaCameraView.setCvCameraViewListener(this);
        
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (javaCameraView != null) {
            javaCameraView.disableView();
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        if (!OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_4_0, this, mLoaderCallBack)) {
            Log.e(TAG, "  OpenCVLoader.initAsync(), not working.");
            mLoaderCallBack.onManagerConnected(LoaderCallbackInterface.SUCCESS);
        } else {
            Log.d(TAG, "  OpenCVLoader.initAsync(), working.");
            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_4_0, this, mLoaderCallBack);
        }

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (javaCameraView != null) {
            javaCameraView.disableView();
        }

    }

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

    @Override
    public void onCameraViewStopped() {
        javaCameraView.disableView();
    }

    @Override
    public Mat onCameraFrame(Mat inputFrame) {
        usedMat = inputFrame;
        return usedMat;
    }
}