FIleObserver and ContentObserver not working in An

问题:

I have issue with both FIleObserver and ContentObserver not working in Android Marshmallow. I am using this thing for detecting changes that happening inside a folder. I set run time permissions for marshmallow. But after that also it shows no events. It works perfectly in other versions. Please help me to solve this problem.

First I tried Content Resolver inside Service for detect folder changes in background.

public class TestService extends Service {

    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        initial();
        return START_STICKY;
    }

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

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

                    @Override
                    public void onChange(boolean selfChange, Uri uri) {

                        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("file", "FILE CHANGE OCCURED " + fileName + " " + path);
                                }
                            } finally {
                                if (cursor != null)  {
                                    cursor.close();
                                }
                            }
                        }
                        super.onChange(selfChange, uri);
                    }
                }
        );

    }
}

And run time permissions as:

private void getPermission(){
    boolean hasPermission = (ContextCompat.checkSelfPermission(this,
            Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED);
    if (!hasPermission) {
        ActivityCompat.requestPermissions(this,
                new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                REQUEST_READ_STORAGE);
    }
}

And received that permissions result in onRequestPermissionsResult. This method didn't work for me. So I tried with FileObserver inside that service. That time also it works in all other platforms, but not Marshmallow.

回答1:

This appears to be a bug in Marshmallow, see here.

You can only try working around it by polling for whatever information you need.

How well this will work for you depends on your use case. I found it usable for tracking download progress: start polling when the download starts, with a one-second interval, and stop when the download finishes.

If you expect very infrequent changes, you can try increasing the interval – at the cost of a potentially higher delay between changes happening and your app picking them up.