c#获取远程文件更新时间

HttpWebRequest myReq = (HttpWebRequest)WebRequest.Create("http://www.moreyun.com/2012/shangxiabangao_0805/144.html");
HttpWebResponse myRes = (HttpWebResponse)myReq.GetResponse();
WebHeaderCollection header = myRes.Headers;
string lastmodify = header["Last-Modified"];
myRes.Close();

string url = "http://www.moreyun.com/2012/shangxiabangao_0805/144.html";
Uri uri = new Uri(url, UriKind.Absolute);
WebClient request = new WebClient();
request.OpenReadAsync(uri);
request.OpenReadCompleted += (s, ev) =>
{
string last = request.ResponseHeaders["Last-Modified"];
MessageBox.Show(last);
};