（转）WP7 断点续传

原文地址：http://www.cnblogs.com/bryht/archive/2012/03/26/2418299.html

断点续传其实就是在请求流的时候请求中间流，而不是每次重新从头来过

HttpWebRequest Myrq = (HttpWebRequest)HttpWebRequest.CreateHttp(URL);

Myrq.Headers["Range"] = "bytes=1024-";//设置Range值 

这句就是请求1024位置开始到末尾的流

如果Myrq.Headers["Range"] = "bytes=1024-2048";

则表示请求1024到2048位置的数据 

有了这个方法，写断点续传就会简单许多了，错略的方法如下

  public void DownFile(string URL, string Filename, ProgressBar Prog)
  {
            //打开上次下载的文件或新建文件
            long lStartPos = 0;
            IsolatedStorageFileStream fs;

            if (IsolatedStorageFile.GetUserStoreForApplication().FileExists(Filename))
            {
                fs = IsolatedStorageFile.GetUserStoreForApplication().OpenFile(Filename, FileMode.Open);
                lStartPos = fs.Length;
                fs.Seek(lStartPos, System.IO.SeekOrigin.Current); //移动文件流中的当前指针
            }
            else
            {
                fs = IsolatedStorageFile.GetUserStoreForApplication().CreateFile(Filename);
                lStartPos = 0;
            }
            try
            {
                HttpWebRequest Myrq = (HttpWebRequest)HttpWebRequest.CreateHttp(URL);
                Myrq.Headers["User-Agent"] = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 1.0.3705)";
                if (lStartPos > 0)
                {
                    Myrq.Headers["Range"] = "bytes=" + lStartPos + "-";//设置Range值
                }
                Myrq.BeginGetResponse(new AsyncCallback((a) =>
                    {
                        var myrp = Myrq.EndGetResponse(a);
                        long totalBytes = myrp.ContentLength + fs.Length;
                        this.Dispatcher.BeginInvoke(() => { Prog.Maximum = (int)totalBytes; });
                        Stream st = myrp.GetResponseStream();
                        //Stream so = new FileStream(Filename, FileMode.Create);
                        long totalDownloadedByte = fs.Length;
                        byte[] by = new byte[1024];
                        int osize = st.Read(by, 0, (int)by.Length);
                        while (osize > 0)
                        {
                            totalDownloadedByte = osize + totalDownloadedByte;
                            fs.Write(by, 0, osize);
                            this.Dispatcher.BeginInvoke(() => { Prog.Value = (int)totalDownloadedByte; });
                            osize = st.Read(by, 0, (int)by.Length);
                        }
                        fs.Close();
                        st.Close();
                        MessageBox.Show("下载完毕!");
                    }), null);
            }
            catch (Exception ex)
            {
                MessageBox.Show("提示" + ex.Message);
            }
        }

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