Detect only screenshot with FileObserver Android

问题:

I am currently developing an application for Android and wanted to know how to detect a screenshot. I tried with FileObserver but the problem is that all events are detected ( when device goes into sleep, message, etc. ) . How to detect only screenshot ?

Thank you in advance !

回答1:

How did you use FileObserver to detect screen shot creation? When using FileObserver, only monitor the file creation event in screen shot directory.

    String path = Environment.getExternalStorageDirectory()
            + File.separator + Environment.DIRECTORY_PICTURES
            + File.separator + "Screenshots" + File.separator;
    Log.d(TAG, path);

    FileObserver fileObserver = new FileObserver(path, FileObserver.CREATE) {
        @Override
        public void onEvent(int event, String path) {
            Log.d(TAG, event + " " + path);
        }
    };

    fileObserver.startWatching();

Don't forget to declare corresponding permissions to access content in SD card.

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

Another solution to detect the screen shot is using ContentObserver, because there will be a record inserted to the system media database after screen shot. Following is the code snippet using ContentObserver to monitor the event. By using ContentObserver, it's not necessary to declare write/read external storage permissions, but you have to do some filters on the file name to make sure it's a screen shot event.

    HandlerThread handlerThread = new HandlerThread("content_observer");
    handlerThread.start();
    final Handler handler = new Handler(handlerThread.getLooper()) {

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
        }
    };

    getContentResolver().registerContentObserver(
            MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
            true,
            new ContentObserver(handler) {
                @Override
                public boolean deliverSelfNotifications() {
                    Log.d(TAG, "deliverSelfNotifications");
                    return super.deliverSelfNotifications();
                }

                @Override
                public void onChange(boolean selfChange) {
                    super.onChange(selfChange);
                }

                @Override
                public void onChange(boolean selfChange, Uri uri) {
                    Log.d(TAG, "onChange " + uri.toString());
                    if (uri.toString().matches(MediaStore.Images.Media.EXTERNAL_CONTENT_URI.toString() + "/[0-9]+")) {

                        Cursor cursor = null;
                        try {
                            cursor = getContentResolver().query(uri, new String[] {
                                    MediaStore.Images.Media.DISPLAY_NAME,
                                    MediaStore.Images.Media.DATA
                            }, null, null, null);
                            if (cursor != null && cursor.moveToFirst()) {
                                final String fileName = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DISPLAY_NAME));
                                final String path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA));
                                // TODO: apply filter on the file name to ensure it's screen shot event
                                Log.d(TAG, "screen shot added " + fileName + " " + path);
                            }
                        } finally {
                            if (cursor != null)  {
                                cursor.close();
                            }
                        }
                    }
                    super.onChange(selfChange, uri);
                }
            }
    );

Updated

If you use second method, you have to request READ_EXTERNAL_STORAGE after version Android M, otherwise it will throw SecurityException. For more information how to request runtime permission, refer here.

回答2:

I have improve the code from alijandro's comment to make it easy-to-use class and fix the problem when content observer has detect the image from camera (should be screenshot image only). Then wrap it to delegate class for convenient to use.

---

• ScreenshotDetectionDelegate.java

public class ScreenshotDetectionDelegate {
    private WeakReference<Activity> activityWeakReference;
    private ScreenshotDetectionListener listener;

    public ScreenshotDetectionDelegate(Activity activityWeakReference, ScreenshotDetectionListener listener) {
        this.activityWeakReference = new WeakReference<>(activityWeakReference);
        this.listener = listener;
    }

    public void startScreenshotDetection() {
        activityWeakReference.get()
                .getContentResolver()
                .registerContentObserver(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, true, contentObserver);
    }

    public void stopScreenshotDetection() {
        activityWeakReference.get().getContentResolver().unregisterContentObserver(contentObserver);
    }

    private ContentObserver contentObserver = new ContentObserver(new Handler()) {
        @Override
        public boolean deliverSelfNotifications() {
            return super.deliverSelfNotifications();
        }

        @Override
        public void onChange(boolean selfChange) {
            super.onChange(selfChange);
        }

        @Override
        public void onChange(boolean selfChange, Uri uri) {
            super.onChange(selfChange, uri);
            if (isReadExternalStoragePermissionGranted()) {
                String path = getFilePathFromContentResolver(activityWeakReference.get(), uri);
                if (isScreenshotPath(path)) {
                    onScreenCaptured(path);
                }
            } else {
                onScreenCapturedWithDeniedPermission();
            }
        }
    };

    private void onScreenCaptured(String path) {
        if (listener != null) {
            listener.onScreenCaptured(path);
        }
    }

    private void onScreenCapturedWithDeniedPermission() {
        if (listener != null) {
            listener.onScreenCapturedWithDeniedPermission();
        }
    }

    private boolean isScreenshotPath(String path) {
        return path != null && path.toLowerCase().contains("screenshots");
    }

    private String getFilePathFromContentResolver(Context context, Uri uri) {
        try {
            Cursor cursor = context.getContentResolver().query(uri, new String[]{
                    MediaStore.Images.Media.DISPLAY_NAME,
                    MediaStore.Images.Media.DATA
            }, null, null, null);
            if (cursor != null && cursor.moveToFirst()) {
                String path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA));
                cursor.close();
                return path;
            }
        } catch (IllegalStateException ignored) {
        }
        return null;
    }

    private boolean isReadExternalStoragePermissionGranted() {
        return ContextCompat.checkSelfPermission(activityWeakReference.get(), Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED;
    }

    public interface ScreenshotDetectionListener {
        void onScreenCaptured(String path);

        void onScreenCapturedWithDeniedPermission();
    }
}

---

• ScreenshotDetectionActivity.java

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.widget.Toast;

public abstract class ScreenshotDetectionActivity extends AppCompatActivity implements ScreenshotDetectionDelegate.ScreenshotDetectionListener {
    private static final int REQUEST_CODE_READ_EXTERNAL_STORAGE_PERMISSION = 3009;

    private ScreenshotDetectionDelegate screenshotDetectionDelegate = new ScreenshotDetectionDelegate(this, this);

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        checkReadExternalStoragePermission();
    }

    @Override
    protected void onStart() {
        super.onStart();
        screenshotDetectionDelegate.startScreenshotDetection();
    }

    @Override
    protected void onStop() {
        super.onStop();
        screenshotDetectionDelegate.stopScreenshotDetection();
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode) {
            case REQUEST_CODE_READ_EXTERNAL_STORAGE_PERMISSION:
                if (grantResults[0] == PackageManager.PERMISSION_DENIED) {
                    showReadExternalStoragePermissionDeniedMessage();
                }
                break;
            default:
                super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        }
    }

    @Override
    public void onScreenCaptured(String path) {
        // Do something when screen was captured
    }

    @Override
    public void onScreenCapturedWithDeniedPermission() {
        // Do something when screen was captured but read external storage permission has denied
    }

    private void checkReadExternalStoragePermission() {
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            requestReadExternalStoragePermission();
        }
    }

    private void requestReadExternalStoragePermission() {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, REQUEST_CODE_READ_EXTERNAL_STORAGE_PERMISSION);
    }

    private void showReadExternalStoragePermissionDeniedMessage() {
        Toast.makeText(this, "Read external storage permission has denied", Toast.LENGTH_SHORT).show();
    }
}

---

• MainActivity.java

import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends ScreenshotDetectionActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public void onScreenCaptured(String path) {
        Toast.make(this, path, Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onScreenCapturedWithDeniedPermission() {
        Toast.make(this, "Please grant read external storage permission for screenshot detection", Toast.LENGTH_SHORT).show();
    }
}

回答3:

You can create FileObserver that only monitors screenshot directory plus only trigger events for file or directory creation. For more information click here.

回答4:

I made the git project for android screenshot.

I used Content Observer.

working fine from API 14 to Recent Version

You can check here

1.ScreenShotContentObserver .class
(original screenshot delete -> inform screenshot taken and give screenshot bitmap )

public class ScreenShotContentObserver extends ContentObserver {


private final String TAG = this.getClass().getSimpleName();
private static final String[] PROJECTION = new String[]{
        MediaStore.Images.Media.DISPLAY_NAME, MediaStore.Images.Media.DATA,
        MediaStore.Images.Media.DATE_ADDED, MediaStore.Images.ImageColumns._ID
};
private static final long DEFAULT_DETECT_WINDOW_SECONDS = 10;
private static final String SORT_ORDER = MediaStore.Images.Media.DATE_ADDED + " DESC";

public static final String FILE_POSTFIX = "FROM_ASS";
private static final String WATERMARK = "Scott";
private ScreenShotListener mListener;
private ContentResolver mContentResolver;
private String lastPath;

public ScreenShotContentObserver(Handler handler, ContentResolver contentResolver, ScreenShotListener listener) {
    super(handler);
    mContentResolver = contentResolver;
    mListener = listener;
}

@Override
public boolean deliverSelfNotifications() {
    Log.e(TAG, "deliverSelfNotifications");
    return super.deliverSelfNotifications();
}

@Override
synchronized public void onChange(boolean selfChange) {
    super.onChange(selfChange);
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
        //above API 16 Pass~!(duplicated call...)
        return;
    }
    Log.e(TAG, "[Start] onChange : " + selfChange);
    try {
        process(MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
        Log.e(TAG, "[Finish] general");
    } catch (Exception e) {
        Log.e(TAG, "[Finish] error : " + e.toString(), e);
    }
}

@Override
synchronized public void onChange(boolean selfChange, Uri uri) {
    super.onChange(selfChange, uri);
    Log.e(TAG, "[Start] onChange : " + selfChange + " / uri : " + uri.toString());

    if (uri.toString().startsWith(MediaStore.Images.Media.EXTERNAL_CONTENT_URI.toString())) {
        try {
            process(uri);
            Log.e(TAG, "[Finish] general");
        } catch (Exception e) {
            Log.e(TAG, "[Finish] error : " + e.toString(), e);
        }
    } else {
        Log.e(TAG, "[Finish] not EXTERNAL_CONTENT_URI ");
    }
}

public void register() {
    Log.d(TAG, "register");
    mContentResolver.registerContentObserver(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, true, this);
}

public void unregister() {
    Log.d(TAG, "unregister");
    mContentResolver.unregisterContentObserver(this);
}

 private boolean process(Uri uri) throws Exception {
    Data result = getLatestData(uri);
    if (result == null) {
        Log.e(TAG, "[Result] result is null!!");
        return false;
    }
    if (lastPath != null && lastPath.equals(result.path)) {
        Log.e(TAG, "[Result] duplicate!!");
        return false;
    }
    long currentTime = System.currentTimeMillis() / 1000;
    if (matchPath(result.path) && matchTime(currentTime, result.dateAdded)) {
        lastPath = result.path;
        Uri screenUri = Uri.parse(MediaStore.Images.Media.EXTERNAL_CONTENT_URI.toString() + "/" + result.id);
        Log.e(TAG, "[Result] This is screenshot!! : " + result.fileName + " | dateAdded : " + result.dateAdded + " / " + currentTime);
        Bitmap bitmap = MediaStore.Images.Media.getBitmap(mContentResolver, screenUri);
        Bitmap copyBitmap = bitmap.copy(bitmap.getConfig(), true);
        bitmap.recycle();
        int temp = mContentResolver.delete(screenUri, null, null);
        Log.e(TAG, "Delete Result : " + temp);
        if (mListener != null) {
            mListener.onScreenshotTaken(copyBitmap, result.fileName);
        }
        return true;
    } else {
        Log.e(TAG, "[Result] No ScreenShot : " + result.fileName);
    }
    return false;
}

private Data getLatestData(Uri uri) throws Exception {
    Data data = null;
    Cursor cursor = null;
    try {
        cursor = mContentResolver.query(uri, PROJECTION, null, null, SORT_ORDER);
        if (cursor != null && cursor.moveToFirst()) {
            long id = cursor.getLong(cursor.getColumnIndex(MediaStore.Images.ImageColumns._ID));
            String fileName = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DISPLAY_NAME));
            String path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA));
            long dateAdded = cursor.getLong(cursor.getColumnIndex(MediaStore.Images.Media.DATE_ADDED));

            if (fileName.contains(FILE_POSTFIX)) {
                if (cursor.moveToNext()) {
                    id = cursor.getLong(cursor.getColumnIndex(MediaStore.Images.ImageColumns._ID));
                    fileName = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DISPLAY_NAME));
                    path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA));
                    dateAdded = cursor.getLong(cursor.getColumnIndex(MediaStore.Images.Media.DATE_ADDED));
                } else {
                    return null;
                }
            }

            data = new Data();
            data.id = id;
            data.fileName = fileName;
            data.path = path;
            data.dateAdded = dateAdded;
            Log.e(TAG, "[Recent File] Name : " + fileName);
        }
    } finally {
        if (cursor != null) {
            cursor.close();
        }
    }
    return data;
}

private boolean matchPath(String path) {
    return (path.toLowerCase().contains("screenshots/") && !path.contains(FILE_POSTFIX));
}

private boolean matchTime(long currentTime, long dateAdded) {
    return Math.abs(currentTime - dateAdded) <= DEFAULT_DETECT_WINDOW_SECONDS;
}

class Data {
    long id;
    String fileName;
    String path;
    long dateAdded;
}  
 }

2. Util.class
   

   public static void saveImage(Context context, Bitmap bitmap, String title) throws Exception {
   OutputStream fOut = null;
   title = title.replaceAll(" ", "+");
   int index = title.lastIndexOf(".png");
   String fileName = title.substring(0, index) + ScreenShotContentObserver.FILE_POSTFIX + ".png";
   final String appDirectoryName = "Screenshots";
   final File imageRoot = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), appDirectoryName);
   imageRoot.mkdirs();
   final File file = new File(imageRoot, fileName);
   fOut = new FileOutputStream(file);
   
   bitmap.compress(Bitmap.CompressFormat.PNG, 100, fOut);
   fOut.flush();
   fOut.close();
   
   ContentValues values = new ContentValues();
   values.put(MediaStore.Images.Media.TITLE, "XXXXX");
   values.put(MediaStore.Images.Media.DESCRIPTION, "description here");
   values.put(MediaStore.Images.Media.DATE_TAKEN, System.currentTimeMillis());
   values.put(MediaStore.Images.ImageColumns.BUCKET_ID, file.hashCode());
   values.put(MediaStore.Images.ImageColumns.BUCKET_DISPLAY_NAME, file.getName());
   values.put("_data", file.getAbsolutePath());
   ContentResolver cr = context.getContentResolver();
   Uri newUri = cr.insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values);
   context.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, newUri));
   }