使用C#下载一个Internet上的文件主要是依靠HttpWebRequest/HttpWebResonse和WebClient。具体处理起来还有同步和异步两种方式，所以我们其实有四种组合。

1、使用HttpWebRequest/HttpWebResonse和WebClient

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);

WebResponse response = request.GetResponse();

Stream stream = response.GetResponseStream();

if (!response.ContentType.ToLower().StartsWith("text/"))

{

    //Value = SaveBinaryFile(response, FileName);

    byte[] buffer = new byte[1024];

    Stream outStream = System.IO.File.Create(FileName);

    Stream inStream = response.GetResponseStream();

    int l;

    do

    {

        l = inStream.Read(buffer, 0, buffer.Length);

        if (l > 0)

            outStream.Write(buffer, 0, l);

    }

    while (l > 0);

    outStream.Close();

    inStream.Close();

}

2、使用WebClient

string url = "http://www.mozilla.org/images/feature-back-cnet.png";

WebClient myWebClient = new WebClient();

myWebClient.DownloadFile(url,"C:\\temp\\feature-back-cnet.png");

3、异步调用

异步调用可参见：