转自：http://blog.csdn.net/yutyliu/article/details/24346459

string t = "";

//整体下载

IEnumerator downfile(string url, string LocalPath,UILabel DesLable)
    {
        Uri u = new Uri(url);
        HttpWebRequest mRequest = (HttpWebRequest)WebRequest.Create(u);
        mRequest.Method = "GET";
        mRequest.ContentType = "application/x-www-form-urlencoded";
        
        HttpWebResponse wr = (HttpWebResponse)mRequest.GetResponse();
        
        Stream sIn = wr.GetResponseStream();
        FileStream fs = new FileStream(LocalPath, FileMode.Create, FileAccess.Write);
        
        long length = wr.ContentLength;
        long i = 0;
        decimal j = 0;
        
        while (i < length)
        {
            byte[] buffer = new byte[1024];
            i += sIn.Read(buffer, 0, buffer.Length);
            fs.Write(buffer, 0, buffer.Length);
            
            if ((i % 1024) == 0)
            {
                j = Math.Round(Convert.ToDecimal((Convert.ToDouble(i) / Convert.ToDouble(length)) * 100), 4);
                t= "当前下载文件大小:" + length.ToString() + "字节 当前下载大小:" + i + "字节 下载进度" + j.ToString() + "%";
                DesLable.text=t.ToString();
            }
            else
            {
                t = "当前下载文件大小:" + length.ToString() + "字节 当前下载大小:" + i + "字节";
                DesLable.text=t.ToString();
            }

yield return false;
            
            
        }
        
        sIn.Close();
        wr.Close();
        fs.Close();

}

string downloadString="已经下载";

//断点下载
    IEnumerator FPointDown(string uri,string saveFile,UILabel DesLable,UISprite LoadSprite)
    {
        //打开网络连接 
        System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(uri);
        System.Net.HttpWebRequest requestGetCount = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(uri);
        long countLength = requestGetCount.GetResponse().ContentLength;
        
        //打开上次下载的文件或新建文件 
        long lStartPos = 0;
        System.IO.FileStream fs;
        if (System.IO.File.Exists(saveFile))
        {
            fs = System.IO.File.OpenWrite(saveFile);
            lStartPos = fs.Length;
            if (countLength - lStartPos <= 0)
            {
                fs.Close();
                t = "已经";
                DesLable.text=t.ToString();
                yield break;
            }
            fs.Seek(lStartPos, System.IO.SeekOrigin.Current); //移动文件流中的当前指针 
        }
        else
        {
            fs = new System.IO.FileStream(saveFile, System.IO.FileMode.Create);
        }
        
        
        if (lStartPos > 0)
        {
            request.AddRange((int)lStartPos); //设置Range值
            print(lStartPos);
        }
        
        //向服务器请求，获得服务器回应数据流 
        System.IO.Stream ns = request.GetResponse().GetResponseStream();
        int len = 1024 * 8;
        
        byte[] nbytes = new byte[len];
        int nReadSize = 0;
        nReadSize = ns.Read(nbytes, 0, len);
        while (nReadSize > 0)
        {
            fs.Write(nbytes, 0, nReadSize);
            nReadSize = ns.Read(nbytes, 0, len);
            t = downloadString+" : " + fs.Length / 1024 + "kb /" + countLength / 1024 + "kb"+"  ----  "+((double)fs.Length/countLength).ToString()+"%";
           
            
            yield return false;
        }
        ns.Close();
        fs.Close();
      //这里放更新安装代码,或者可以测试这个下载的包有没有出错,验证sha和md5