C# 抓去网站图片

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/// <summary>
/// 提取图片
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void btnOK_Click(object sender, EventArgs e)
{
      WebClient client = new WebClient();
      client.Encoding = Encoding.UTF8;
      string str = client.DownloadString(txtHTML.Text.Trim());
      MatchCollection mc = Regex.Matches(str, "<img.+?src=(['\"]?)([^>\\s]+)\\1.*?>");
      int index = 0;
      foreach (Match item in mc)
      {
          string imgpath = item.Groups[2].Value;
          lbImage.Text = imgpath;
          if (imgpath.IndexOf("http:") > -1)
          {
               client.DownloadFile(imgpath, @"D:\Imges\" + DateTime.Now.Millisecond + index + ".jpg");
           }
           else
           {
               imgpath = txtHTML.Text.Trim() + imgpath;
               client.DownloadFile(imgpath, @"D:\Imges\" + DateTime.Now.Millisecond + index + ".jpg");
            }
               index++;
       }
       MessageBox.Show("OK!");
}