public static String showFileSize(long size) {
        String fileSize;
        if (size < KB)
            fileSize = size + "B";
        else if (size < MB)
            fileSize = String.format("%.1f", size / KB) + "KB";
        else if (size < GB)
            fileSize = String.format("%.1f", size / MB) + "MB";
        else
            fileSize = String.format("%.1f", size / GB) + "GB";

        return fileSize;
    }

    /** 显示SD卡剩余空间 */
    public static String showFileAvailable() {
        String result = "";
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            StatFs sf = new StatFs(Environment.getExternalStorageDirectory().getPath());
            long blockSize = sf.getBlockSize();
            long blockCount = sf.getBlockCount();
            long availCount = sf.getAvailableBlocks();
            return showFileSize(availCount * blockSize) + " / " + showFileSize(blockSize * blockCount);
        }
        return result;

          if (!mHistory.contains(url))
                mHistory.add(0, url);

    /** 删除文件 */
    private void deleteFile(final FileAdapter adapter, final PFile f, final int position) {
        new AlertDialog.Builder(getActivity()).setIcon(android.R.drawable.ic_dialog_alert).setTitle(R.string.file_delete).setMessage(getString(R.string.file_delete_confirm, f.title)).setNegativeButton(android.R.string.yes, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                try {
                    File file = new File(f.path);
                    if (file.canRead() && file.exists())
                        file.delete();
                    FileBusiness.deleteFile(getActivity(), f);
                    adapter.delete(position);
                } catch (Exception e) {

                }
            }

        }).setPositiveButton(android.R.string.no, null).show();
    }

    /** 重命名文件 */
    private void renameFile(final FileAdapter adapter, final PFile f, final int position) {
        final EditText et = new EditText(getActivity());
        et.setText(f.title);
        new AlertDialog.Builder(getActivity()).setTitle(R.string.file_rename).setIcon(android.R.drawable.ic_dialog_info).setView(et).setNegativeButton(android.R.string.yes, new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                String name = et.getText().toString().trim();
                if (name == null || name.trim().equals("") || name.trim().equals(f.title))
                    return;

                try {
                    File fromFile = new File(f.path);
                    File nf = new File(fromFile.getParent(), name.trim());
                    if (nf.exists()) {
                        Toast.makeText(getActivity(), R.string.file_rename_exists, Toast.LENGTH_LONG).show();
                    } else if (fromFile.renameTo(nf)) {
                        f.title = name;
                        f.path = nf.getPath();
                        FileBusiness.renameFile(getActivity(), f);
                        adapter.notifyDataSetChanged();
                    }
                } catch (SecurityException se) {
                    Toast.makeText(getActivity(), R.string.file_rename_failed, Toast.LENGTH_LONG).show();
                }
            }

        }).setPositiveButton(android.R.string.no, null).show();