[Android] Multi Media 7: Camera2 API 를 사용한 동영상 저장

동영상도 직전 포스팅인 오디오 녹음과 같이 MediaRecorder 객체를 생성하여, 초기화를 해준 뒤 start() 메서드를 사용하여 기록할 수 있다.

 

Camera2 API를 이용하여 카메라 미리보기를 생성하고, Record 버튼을 눌러 동영상을 촬영한 뒤 저장까지 해보려고 한다. 

 

Camera2 API를 이용하여 미리보기를 만들고 이를 캡쳐하는 것은 Multi Media 5 포스팅에서 다뤘으므로 생략하고, 이번 예제는 일반 TextureView 가 아닌 AutoFitTextureView를 아래와 같이 따로 생성하여 그 위에 FrameLayout을 올려 구성했다.

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◎AutoFitTextureView.java

package com.example.samplecamera2recorder;

import android.content.Context;
import android.util.AttributeSet;
import android.view.TextureView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

public class AutoFitTextureView extends TextureView {

    private int mRatioWidth = 0;
    private int mRatioHeight = 0;

    public AutoFitTextureView(@NonNull Context context) {
        super(context);
    }

    public AutoFitTextureView(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public AutoFitTextureView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }
    /**
     * View 의 대략적인 비율을 설정한다.
     * 이 View의 사이즈는 비율에 따라 측정되며, 각 인자는 상대값이다.
     * 즉, setAspectRatio(2, 3) = setAspectRatio(4, 6) 이다.
     * */
    public void setAspectRatio(int width, int height) {
        if(width < 0 || height < 0) {
            throw new IllegalArgumentException("Size cannot be negative");
        }
        mRatioHeight = height;
        mRatioWidth = width;
        requestLayout();
    }

    @Override
    // 해당 클래스의 Width, Height 설정
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        if (0 == mRatioWidth || 0 == mRatioHeight) {
            setMeasuredDimension(width, height);
        } else {
            if (width < height * mRatioWidth / mRatioHeight) {
                setMeasuredDimension(width, width * mRatioHeight / mRatioWidth);
            } else {
                setMeasuredDimension(height * mRatioWidth / mRatioHeight, height);
            }
        }
    }
}

 

◎activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent">

    <com.example.samplecamera2recorder.AutoFitTextureView
            android:id="@+id/texture"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"/>

    <FrameLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_alignParentStart="true"
            android:layout_below="@id/texture"
            android:background="#4285f4">

        <Button
                android:id="@+id/video"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                android:text="Record" />

        <ImageButton
                android:id="@+id/info"
                android:contentDescription="Info"
                style="@android:style/Widget.Material.Light.Button.Borderless"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_vertical|right"
                android:padding="20dp"
                android:src="@android:drawable/ic_dialog_info" />

    </FrameLayout>

</RelativeLayout>

 

◎MainActivity.java

package com.example.samplecamera2recorder;

import android.app.Activity;
import android.app.Dialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.res.Configuration;
import android.graphics.Matrix;
import android.graphics.RectF;
import android.graphics.SurfaceTexture;
import android.hardware.camera2.*;
import android.hardware.camera2.params.StreamConfigurationMap;
import android.media.MediaRecorder;
import android.net.Uri;
import android.os.Environment;
import android.os.Handler;
import android.os.HandlerThread;
import android.util.Log;
import android.util.Size;
import android.util.SparseIntArray;
import android.view.Surface;
import android.view.TextureView;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import androidx.core.app.ActivityCompat;
import androidx.fragment.app.DialogFragment;
import androidx.fragment.app.Fragment;
import com.yanzhenjie.permission.Action;
import com.yanzhenjie.permission.AndPermission;
import com.yanzhenjie.permission.runtime.Permission;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

public class MainActivity extends AppCompatActivity {

    private static final int SENSOR_ORIENTATION_DEFAULT_DEGREES = 90;
    private static final int SENSOR_ORIENTATION_INVERSE_DEGREES = 270;

    private static final SparseIntArray DEFAULT_ORIENTATIONS = new SparseIntArray();
    private static final SparseIntArray INVERSE_ORIENTATIONS = new SparseIntArray();

    private static final String TAG = "Camera2VideoFragment";

    static {
        DEFAULT_ORIENTATIONS.append(Surface.ROTATION_0, 90);
        DEFAULT_ORIENTATIONS.append(Surface.ROTATION_90, 0);
        DEFAULT_ORIENTATIONS.append(Surface.ROTATION_180, 270);
        DEFAULT_ORIENTATIONS.append(Surface.ROTATION_270, 180);
    }

    static {
        INVERSE_ORIENTATIONS.append(Surface.ROTATION_0, 270);
        INVERSE_ORIENTATIONS.append(Surface.ROTATION_90, 180);
        INVERSE_ORIENTATIONS.append(Surface.ROTATION_180, 90);
        INVERSE_ORIENTATIONS.append(Surface.ROTATION_270, 0);
    }

    // 카메라 미리보기를 띄우기 위한 AutoFitTextureView 객체
    private AutoFitTextureView mTextureView;

    // 녹화 버튼
    private Button mButtonVideo;

    // CameraDevice
    private CameraDevice mCameraDevice;

    // 카메라 미리보기를 위한 CameraCaptureSession
    private CameraCaptureSession mPreviewSession;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTextureView = (AutoFitTextureView) findViewById(R.id.texture);
        mButtonVideo = (Button) findViewById(R.id.video);
        mButtonVideo.setOnClickListener(new Button.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mIsRecordingVideo) {
                    stopRecordingVideo();
                } else {
                    startRecordingVideo();
                }
            }
        });
        findViewById(R.id.info).setOnClickListener(new Button.OnClickListener() {
            @Override
            public void onClick(View view) {
                AlertDialog show = new AlertDialog.Builder(MainActivity.this)
                        .setMessage("This sample demonstrates how to record video using Camera2 API.")
                        .setPositiveButton(android.R.string.ok, null)
                        .show();
            }
        });
    }

    // TextureView 객체의 Life Cycle 을 다루기 위한 콜백 핸들러
    private TextureView.SurfaceTextureListener mSurfaceTextureListener
            = new TextureView.SurfaceTextureListener() {

        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture,
                                              int width, int height) {
            openCamera(width, height);
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture,
                                                int width, int height) {
            configureTransform(width, height);
        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
            return true;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {
        }
    };

    // 카메라 미리보기 사이즈
    private Size mPreviewSize;

    // Video Recording 사이즈
    private Size mVideoSize;

    // 재생을 위한 MediaRecorder
    private MediaRecorder mMediaRecorder;

    // 앱이 비디오를 녹화 중인지 확인하기 위한 변수
    private boolean mIsRecordingVideo;

    // UI 객체를 멈추게 하지 않기 위해 추가하는 Thread
    private HandlerThread mBackgroundThread;

    // Thread 를 제어할 Handler
    private Handler mBackgroundHandler;

    /**
     * Semaphore 는 특정 자원이나 특정 연산을 동시에 사용하거나 호출할 수 있는 스레드의 수를 제한하고자 할 때 사용한다.
     * Semaphore 클래스는 가상의 Permit 을 만들어 내부 상태를 관리하며, 클래스를 생성할 때 인자로 Permit 의 수를 넘겨주게 되어 있다.
     *
     * 현재 사용할 수 있는 남은 permit이 없는 경우 (permit = 0), acquire 메소드는 남는 permit이 생기거나, 인터럽트가 걸리거나,
     * 지정한 시간을 넘겨 타임아웃이 걸리기 전까지 대기한다.
     *
     * release 메소드는 확보했던 permit 을 다시 세마포어에 반납하는 기능을 한다.
     * */
    private Semaphore mCameraOpenCloseLock = new Semaphore(1);

    // CameraDevice 객체의 상태가 변경될 때 호출되는 콜백 핸들러
    private CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {

        @Override
        public void onOpened(@NonNull CameraDevice cameraDevice) {
            mCameraDevice = cameraDevice;
            startPreview();
            mCameraOpenCloseLock.release();
            if (null != mTextureView) {
                configureTransform(mTextureView.getWidth(), mTextureView.getHeight());
            }
        }

        @Override
        public void onDisconnected(@NonNull CameraDevice cameraDevice) {
            mCameraOpenCloseLock.release();
            cameraDevice.close();
            mCameraDevice = null;
        }

        @Override
        public void onError(@NonNull CameraDevice cameraDevice, int error) {
            mCameraOpenCloseLock.release();
            cameraDevice.close();
            mCameraDevice = null;
            finish();
        }
    };

    private Integer mSensorOrientation;
    private String mNextVideoAbsolutePath;
    private File mNextVideo;
    private CaptureRequest.Builder mPreviewBuilder;

    /**
     * In this sample, we choose a video size with 3x4 aspect ratio. Also, we don't use sizes
     * larger than 1080p, since MediaRecorder cannot handle such a high-resolution video.
     *
     * @param choices The list of available sizes
     * @return The video size
     */
    private static Size chooseVideoSize(Size[] choices) {
        for (Size size : choices) {
            if (size.getWidth() == size.getHeight() * 4 / 3 && size.getWidth() <= 1080) {
                return size;
            }
        }
        Log.e(TAG, "Couldn't find any suitable video size");
        return choices[choices.length - 1];
    }

    /**
     * Given {@code choices} of {@code Size}s supported by a camera, chooses the smallest one whose
     * width and height are at least as large as the respective requested values, and whose aspect
     * ratio matches with the specified value.
     *
     * @param choices     The list of sizes that the camera supports for the intended output class
     * @param width       The minimum desired width
     * @param height      The minimum desired height
     * @param aspectRatio The aspect ratio
     * @return The optimal {@code Size}, or an arbitrary one if none were big enough
     */
    private static Size chooseOptimalSize(Size[] choices, int width, int height, Size aspectRatio) {
        // Collect the supported resolutions that are at least as big as the preview Surface
        List<Size> bigEnough = new ArrayList<>();
        int w = aspectRatio.getWidth();
        int h = aspectRatio.getHeight();
        for (Size option : choices) {
            if (option.getHeight() == option.getWidth() * h / w &&
                    option.getWidth() >= width && option.getHeight() >= height) {
                bigEnough.add(option);
            }
        }

        // Pick the smallest of those, assuming we found any
        if (bigEnough.size() > 0) {
            return Collections.min(bigEnough, new CompareSizesByArea());
        } else {
            Log.e(TAG, "Couldn't find any suitable preview size");
            return choices[0];
        }
    }

    @Override
    public void onResume() {
        super.onResume();
        startBackgroundThread();
        if (mTextureView.isAvailable()) {
            openCamera(mTextureView.getWidth(), mTextureView.getHeight());
        } else {
            mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);
        }
    }

    @Override
    public void onPause() {
        closeCamera();
        stopBackgroundThread();
        super.onPause();
    }
    
    // background thread 와 Handler 시작
    private void startBackgroundThread() {
        mBackgroundThread = new HandlerThread("CameraBackground");
        mBackgroundThread.start();
        mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
    }

    // background thread 와 Handler 중지
    private void stopBackgroundThread() {
        mBackgroundThread.quitSafely();
        try {
            mBackgroundThread.join();
            mBackgroundThread = null;
            mBackgroundHandler = null;
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    
    // mStateCallback 이 호출할 Camera Open 메서드
    private void openCamera(int width, int height) {

        AndPermission.with(this)
                .runtime()
                .permission(
                        Permission.CAMERA,
                        Permission.WRITE_EXTERNAL_STORAGE,
                        Permission.RECORD_AUDIO)
                .onGranted(new Action<List<String>>() {
                    @Override
                    public void onAction(List<String> permissions) {

                    }
                })
                .start();

        if (isFinishing()) {
            return;
        }
        CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {
            Log.d(TAG, "tryAcquire");
            if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {
                throw new RuntimeException("Time out waiting to lock camera opening.");
            }
            String cameraId = manager.getCameraIdList()[0];

            // Choose the sizes for camera preview and video recording
            CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
            StreamConfigurationMap map = characteristics
                    .get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            mSensorOrientation = characteristics.get(CameraCharacteristics.SENSOR_ORIENTATION);
            if (map == null) {
                throw new RuntimeException("Cannot get available preview/video sizes");
            }
            mVideoSize = chooseVideoSize(map.getOutputSizes(MediaRecorder.class));
            mPreviewSize = chooseOptimalSize(map.getOutputSizes(SurfaceTexture.class),
                    width, height, mVideoSize);

            int orientation = getResources().getConfiguration().orientation;
            if (orientation == Configuration.ORIENTATION_LANDSCAPE) {
                mTextureView.setAspectRatio(mPreviewSize.getWidth(), mPreviewSize.getHeight());
            } else {
                mTextureView.setAspectRatio(mPreviewSize.getHeight(), mPreviewSize.getWidth());
            }
            configureTransform(width, height);
            mMediaRecorder = new MediaRecorder();
            if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {

                return;
            }
            manager.openCamera(cameraId, mStateCallback, null);
        } catch (CameraAccessException e) {
            Toast.makeText(MainActivity.this, "Cannot access the camera.", Toast.LENGTH_SHORT).show();
            finish();
        } catch (NullPointerException e) {
            // Currently an NPE is thrown when the Camera2API is used but not supported on the
            // device this code runs.
        } catch (InterruptedException e) {
            throw new RuntimeException("Interrupted while trying to lock camera opening.");
        }
    }

    private void closeCamera() {
        try {
            mCameraOpenCloseLock.acquire();
            closePreviewSession();
            if (null != mCameraDevice) {
                mCameraDevice.close();
                mCameraDevice = null;
            }
            if (null != mMediaRecorder) {
                mMediaRecorder.release();
                mMediaRecorder = null;
            }
        } catch (InterruptedException e) {
            throw new RuntimeException("Interrupted while trying to lock camera closing.");
        } finally {
            mCameraOpenCloseLock.release();
        }
    }

    /**
     * 카메라 미리보기 시작
     */
    private void startPreview() {
        if (null == mCameraDevice || !mTextureView.isAvailable() || null == mPreviewSize) {
            return;
        }
        try {
            closePreviewSession();
            SurfaceTexture texture = mTextureView.getSurfaceTexture();
            assert texture != null;
            texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
            mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);

            Surface previewSurface = new Surface(texture);
            mPreviewBuilder.addTarget(previewSurface);

            mCameraDevice.createCaptureSession(Collections.singletonList(previewSurface),
                    new CameraCaptureSession.StateCallback() {

                        @Override
                        public void onConfigured(@NonNull CameraCaptureSession session) {
                            mPreviewSession = session;
                            updatePreview();
                        }

                        @Override
                        public void onConfigureFailed(@NonNull CameraCaptureSession session) {
                            Toast.makeText(MainActivity.this, "Failed", Toast.LENGTH_SHORT).show();
                        }
                    }, mBackgroundHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    // Camera 미리보기 update
    private void updatePreview() {
        if (null == mCameraDevice) {
            return;
        }
        try {
            setUpCaptureRequestBuilder(mPreviewBuilder);
            HandlerThread thread = new HandlerThread("CameraPreview");
            thread.start();
            mPreviewSession.setRepeatingRequest(mPreviewBuilder.build(), null, mBackgroundHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void setUpCaptureRequestBuilder(CaptureRequest.Builder builder) {
        builder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
    }

    /**
     * mTextureView에 Matrix 변환을 설정하기 위한 메서드
     * @param viewWidth  The width of `mTextureView`
     * @param viewHeight The height of `mTextureView`
     */
    private void configureTransform(int viewWidth, int viewHeight) {

        if (null == mTextureView || null == mPreviewSize ) {
            return;
        }
        int rotation = getWindowManager().getDefaultDisplay().getRotation();
        Matrix matrix = new Matrix();
        RectF viewRect = new RectF(0, 0, viewWidth, viewHeight);
        RectF bufferRect = new RectF(0, 0, mPreviewSize.getHeight(), mPreviewSize.getWidth());
        float centerX = viewRect.centerX();
        float centerY = viewRect.centerY();
        if (Surface.ROTATION_90 == rotation || Surface.ROTATION_270 == rotation) {
            bufferRect.offset(centerX - bufferRect.centerX(), centerY - bufferRect.centerY());
            matrix.setRectToRect(viewRect, bufferRect, Matrix.ScaleToFit.FILL);
            float scale = Math.max(
                    (float) viewHeight / mPreviewSize.getHeight(),
                    (float) viewWidth / mPreviewSize.getWidth());
            matrix.postScale(scale, scale, centerX, centerY);
            matrix.postRotate(90 * (rotation - 2), centerX, centerY);
        }
        mTextureView.setTransform(matrix);
    }

    // MediaRecorder 초기 설정
    private void setUpMediaRecorder() throws IOException {

        mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
        mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);

        File path = new File (Environment.getExternalStorageDirectory()+"/DCIM" + "/camtest");
        if (!path.exists()) {
            path.mkdirs();
        }

        String fileName = String.format("%d.mp4", System.currentTimeMillis());
        mNextVideo = new File(path, fileName);
        mNextVideoAbsolutePath = mNextVideo.getAbsolutePath();

        mMediaRecorder.setOutputFile(mNextVideoAbsolutePath);
        mMediaRecorder.setVideoEncodingBitRate(10000000);
        mMediaRecorder.setVideoFrameRate(30);
        mMediaRecorder.setVideoSize(mVideoSize.getWidth(), mVideoSize.getHeight());
        mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264);
        mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
        int rotation = getWindowManager().getDefaultDisplay().getRotation();
        switch (mSensorOrientation) {
            case SENSOR_ORIENTATION_DEFAULT_DEGREES:
                mMediaRecorder.setOrientationHint(DEFAULT_ORIENTATIONS.get(rotation));
                break;
            case SENSOR_ORIENTATION_INVERSE_DEGREES:
                mMediaRecorder.setOrientationHint(INVERSE_ORIENTATIONS.get(rotation));
                break;
        }
        mMediaRecorder.prepare();
    }

    // MediaRecorder 시작
    private void startRecordingVideo() {
        if (null == mCameraDevice || !mTextureView.isAvailable() || null == mPreviewSize) {
            return;
        }
        try {
            closePreviewSession();
            setUpMediaRecorder();
            SurfaceTexture texture = mTextureView.getSurfaceTexture();
            assert texture != null;
            texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
            mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_RECORD);
            List<Surface> surfaces = new ArrayList<>();

            // Set up Surface for the camera preview
            Surface previewSurface = new Surface(texture);
            surfaces.add(previewSurface);
            mPreviewBuilder.addTarget(previewSurface);

            // Set up Surface for the MediaRecorder
            Surface recorderSurface = mMediaRecorder.getSurface();
            surfaces.add(recorderSurface);
            mPreviewBuilder.addTarget(recorderSurface);

            // Start a capture session
            // Once the session starts, we can update the UI and start recording
            mCameraDevice.createCaptureSession(surfaces, new CameraCaptureSession.StateCallback() {

                @Override
                public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
                    mPreviewSession = cameraCaptureSession;
                    updatePreview();
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            // UI
                            mButtonVideo.setText("Stop");
                            mIsRecordingVideo = true;

                            // Start recording
                            mMediaRecorder.start();
                        }
                    });
                }

                @Override
                public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
                    Toast.makeText(MainActivity.this, "Failed", Toast.LENGTH_SHORT).show();
                }
            }, mBackgroundHandler);
        } catch (CameraAccessException | IOException e) {
            e.printStackTrace();
        }
    }

    // mPreviewSession 리소스 해제
    private void closePreviewSession() {
        if (mPreviewSession != null) {
            mPreviewSession.close();
            mPreviewSession = null;
        }
    }

    private void stopRecordingVideo() {
        // UI
        mIsRecordingVideo = false;
        mButtonVideo.setText("Record");
        // Stop recording
        mMediaRecorder.stop();
        mMediaRecorder.reset();

        Intent mediaScanIntent = new Intent( Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        mediaScanIntent.setData(Uri.fromFile(mNextVideo));
        sendBroadcast(mediaScanIntent);

        Toast.makeText(MainActivity.this, "Video saved: " + mNextVideoAbsolutePath,
                Toast.LENGTH_SHORT).show();
        Log.d(TAG, "Video saved: " + mNextVideoAbsolutePath);

        mNextVideoAbsolutePath = null;
        startPreview();
    }

    /**
     * Compares two {@code Size}s based on their areas.
     */
    static class CompareSizesByArea implements Comparator<Size> {

        @Override
        public int compare(Size lhs, Size rhs) {
            // We cast here to ensure the multiplications won't overflow
            return Long.signum((long) lhs.getWidth() * lhs.getHeight() -
                    (long) rhs.getWidth() * rhs.getHeight());
        }

    }

    public static class ErrorDialog extends DialogFragment {

        private static final String ARG_MESSAGE = "message";

        public static ErrorDialog newInstance(String message) {
            ErrorDialog dialog = new ErrorDialog();
            Bundle args = new Bundle();
            args.putString(ARG_MESSAGE, message);
            dialog.setArguments(args);
            return dialog;
        }

        @Override
        public Dialog onCreateDialog(Bundle savedInstanceState) {
            final Activity activity = getActivity();
            return new AlertDialog.Builder(activity)
                    .setMessage(getArguments().getString(ARG_MESSAGE))
                    .setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {
                            activity.finish();
                        }
                    })
                    .create();
        }

    }

}

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