Helper.java

    private ArrayList<String> getAllShownImagesPath(Activity activity) {
        Uri uri;
        Cursor cursor;
        int column_index_data;
        ArrayList<String> listOfAllImages = new ArrayList<String>();
        String absolutePathOfImage = null;
        uri = android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI;

        String[] projection = {MediaStore.MediaColumns.DATA,
                MediaStore.Images.Media.BUCKET_DISPLAY_NAME};

        cursor = activity.getContentResolver().query(uri, projection, null,
                null, null);

        assert cursor != null;
        column_index_data = cursor.getColumnIndexOrThrow(MediaStore.MediaColumns.DATA);
        while (cursor.moveToNext()) {
            absolutePathOfImage = cursor.getString(column_index_data);

            listOfAllImages.add(absolutePathOfImage);
        }
        return listOfAllImages;
    }