MediaStore.Images.Media.EXTERNAL_CONTENT_URI

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

String sortOrder = MediaStore.Images.Media.DATE_TAKEN + " DESC ";

//一个辅助集合，防止同一目录被扫描多次
HashSet<String> dirPaths = new HashSet<String>();

while (cursor.moveToNext()) {
  // 获取图片的路径
  String path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.ImageColumns.DATA));
  String bucketName = cursor.getString(cursor.getColumnIndex(MediaStore.Images.ImageColumns.BUCKET_DISPLAY_NAME));

  if (TextUtils.isEmpty(allFolderItem.coverImagePath)) {
    allFolderItem.coverImagePath = path;
  }

  File parentFile = new File(path).getParentFile();
  if (parentFile == null) continue;

  String dirPath = parentFile.getAbsolutePath();

  PicFolderItem folderItem = null;
  // 利用一个HashSet防止多次扫描同一个文件夹（不加这个判断，图片多起来还是相当恐怖的~~）
  if (dirPaths.contains(dirPath)) {
    continue;
  } else {
    dirPaths.add(dirPath);

    boolean isNew = true;
    //判断一下是否dirPath不同，但是bucketName相同
    for (PicFolderItem item : picList) {
      if (item.name.equals(bucketName)) {
        folderItem = item;
        item.addParentPath(dirPath);
        isNew = false;
        break;
      }
    }

    if (isNew) {
      folderItem = new PicFolderItem();
      folderItem.coverImagePath = path;
      folderItem.name = bucketName;
      folderItem.addParentPath(dirPath);
    }
  }

  String[] array = parentFile.list(new FilenameFilter() {
    @Override
    public boolean accept(File dir, String filename) {
      if (filename.endsWith(".jpg")
          || filename.endsWith(".png")
          || filename.endsWith(".jpeg"))
        return true;
      return false;
    }
  });

  int arrayCount = array == null ? 0 : array.length;
  folderItem.count += arrayCount;
  if (!picList.contains(folderItem) && arrayCount > 0) {
    picList.add(folderItem);
  }
}

 public static boolean isFileExist(String path) {
  File file = new File(path);
  if (file == null || !file.exists()) {
    return false;
  }
  return true;
  }

//一个辅助集合，防止统一目录查询多次
HashSet<String> dirPaths = new HashSet<String>();

String[] array = parentFile.list(new FilenameFilter() {
            @Override
            public boolean accept(File dir, String filename) {
              if (filename.endsWith(".jpg")
                  || filename.endsWith(".png")
                  || filename.endsWith(".jpeg"))
                return true;
              return false;
            }
          });

File dirFile = new File(dir);
String[] list = dirFile.list(new FilenameFilter() {
  @Override
  public boolean accept(File dir, String filename) {
    if (filename.endsWith(".jpg") || filename.endsWith(".png")
        || filename.endsWith(".jpeg"))
      return true;
    return false;
  }
});

Collections.sort(strings, new Comparator<String>() {
        @Override
        public int compare(String lhs, String rhs) {
          Long time1 = new File(lhs).lastModified();
          Long time2 = new File(rhs).lastModified();
          return time2.compareTo(time1);
        }
        });

String selection = MediaStore.Images.ImageColumns.BUCKET_DISPLAY_NAME + " = '" + 目录名称 + "' ";

String sortOrder = MediaStore.Images.Media.DATE_TAKEN + " DESC limit " + PAGE_SIZE + " offset " + pageIndex * PAGE_SIZE;