判断是否正在扫描Media文件（从系统图库源码获得）

  public static final boolean isMediaScannerScanning(final ContentResolver cr) {
        boolean result = false;
        final Cursor cursor = query(cr, MediaStore.getMediaScannerUri(), new String[] { MediaStore.MEDIA_SCANNER_VOLUME }, null,
                null, null);
        if (cursor != null) {
            if (cursor.getCount() == 1) {
                cursor.moveToFirst();
                result = "external".equals(cursor.getString(0));
            }
            cursor.close();
        }
        Log.i("====isMediaScannerScanning======", "===result===="+result);
        return result;
    }

return false 没有正在扫描

return true 正在扫描