怎样从web服务器上下载文件（c#）

/// <summary> 下载文件</summary>
/// <param name="URL">下载文件地址</param>
/// <param name="Filename">下载后的存放地址</param>
/// <param name="Prog">用于显示的进度条</param>
public static void DownLoadFile(string URL, string filename, System.Windows.Forms.ProgressBar prog)
{
try
{
System.Net.HttpWebRequest Myrq = (System.Net.HttpWebRequest)
System.Net.HttpWebRequest.Create(URL);
System.Net.HttpWebResponse myrp = (System.Net.HttpWebResponse)Myrq.GetResponse();
long totalBytes = myrp.ContentLength;
if (prog != null)
{
prog.Maximum = (int)totalBytes;
}
System.IO.Stream st = myrp.GetResponseStream();
System.IO.Stream so = new System.IO.FileStream(filename, System.IO.FileMode.Create);
long totalDownloadedByte = 0;
byte[] by = new byte[1024];
int osize = st.Read(by, 0, (int)by.Length);
while (osize > 0)
{
totalDownloadedByte = osize + totalDownloadedByte;
System.Windows.Forms.Application.DoEvents();
so.Write(by, 0, osize);
if (prog != null)
{
prog.Value = (int)totalDownloadedByte;
}
osize = st.Read(by, 0, (int)by.Length);
}
so.Close();
st.Close();
}
catch (System.Exception)
{
throw;
}
}