/// <summary>
/// 下载文件
/// </summary>
/// <param name="URL">下载文件地址</param>
/// <param name="Filename">下载后另存为（全路径）</param>
private bool DownloadFile(string URL, string filename)
{
  try
  {
    System.Net.HttpWebRequest Myrq = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(URL);
    System.Net.HttpWebResponse myrp = (System.Net.HttpWebResponse)Myrq.GetResponse();
    System.IO.Stream st = myrp.GetResponseStream();
    System.IO.Stream so = new System.IO.FileStream(filename, System.IO.FileMode.Create);
    byte[] by = new byte[1024];
    int osize = st.Read(by, 0, (int)by.Length);
    while (osize > 0)
    {
      so.Write(by, 0, osize);
      osize = st.Read(by, 0, (int)by.Length);
    }
    so.Close();
    st.Close();
    myrp.Close();
    Myrq.Abort();
    return true;
  }
  catch (System.Exception e)
  {
    writeLogFile(e.Message, true);
    return false;
  }
}