Detect only screenshot with FileObserver Android

Question

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 !

Answer 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.

Answer 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();
    }
}