问Base64 url在Android和C#之间的安全编码和解码

EN

    public string UrlEncode(string str)
    {
        if (str == null || str == "")
        {
            return null;
        }

        byte[] bytesToEncode = System.Text.UTF8Encoding.UTF8.GetBytes(str);
        String returnVal = System.Convert.ToBase64String(bytesToEncode);

        return returnVal.TrimEnd('=').Replace('+', '-').Replace('/', '_');
    }

    public string UrlDecode(string str)
    {
        if (str == null || str == "")
        {
            return null;
        }

        str.Replace('-', '+');
        str.Replace('_', '/');

        int paddings = str.Length % 4;
        if (paddings > 0)
        {
            str += new string('=', 4 - paddings);
        }

        byte[] encodedDataAsBytes = System.Convert.FromBase64String(str);
        string returnVal = System.Text.UTF8Encoding.UTF8.GetString(encodedDataAsBytes);
        return returnVal;
    }