Question

我是C＃的新手，正在处理从Web上抓取URL的窗口应用程序。应用程序需要Internet连接才能从Internet收集URL。问题是当没有互联网连接时发生。并且应用程序显示此类型的错误。

未处理的类型＆＃39; System.Net.WebException＆＃39;发生在 System.dll附加信息：远程名称不可能已解决：＆＃39; www.google.com＆＃39;

问题是我写的那段代码告诉用户，没有互联网连接。而不是显示这种类型的Bug。这是我正在处理的代码。

listBox1.Items.Clear();
            StringBuilder sb = new StringBuilder();
            byte[] ResultsBuffer = new byte[8192];
            string SearchResults = "http://www.google.com/search?num=1000&q=" + txtKeyWords.Text.Trim();
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(SearchResults);
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream resStream = response.GetResponseStream();
            string tempString = null;
            int count = 0;
            do
            {
                count = resStream.Read(ResultsBuffer, 0, ResultsBuffer.Length);
                if (count != 0)
                {
                    tempString = Encoding.ASCII.GetString(ResultsBuffer, 0, count);
                    sb.Append(tempString);
                }
            }
            while (count > 0);
            string sbb = sb.ToString();

            HtmlAgilityPack.HtmlDocument html = new HtmlAgilityPack.HtmlDocument();
            html.OptionOutputAsXml = true;
            html.LoadHtml(sbb);
            HtmlNode doc = html.DocumentNode;

            foreach (HtmlNode link in doc.SelectNodes("//a[@href]"))
            {
                //HtmlAttribute att = link.Attributes["href"];
                string hrefValue = link.GetAttributeValue("href", string.Empty);
                if (!hrefValue.ToString().ToUpper().Contains("GOOGLE") && hrefValue.ToString().Contains("/url?q=") && hrefValue.ToString().ToUpper().Contains("HTTP://"))
                {
                    int index = hrefValue.IndexOf("&");
                    if (index > 0)
                    {
                        hrefValue = hrefValue.Substring(0, index);
                        listBox1.Items.Add(hrefValue.Replace("/url?q=", ""));
                    }
                }
            }

Answer 1

您可以这样做：

//Include everything that could possibly throw an exception in the try brackets
try
{
   HttpWebRequest request = (HttpWebRequest)WebRequest.Create(SearchResults);
   HttpWebResponse response = (HttpWebResponse)request.GetResponse();
   Stream resStream = response.GetResponseStream();
}
catch (Exception e) // Here we are catching your bug-the unhandled exception
{
  MessageBox.Show("You do not have an internet connection");
}

这就是为什么我的答案不完整，需要您做更多工作的原因：除了没有互联网，您可以收到更多例外情况。这个尝试捕获将捕获所有这些。您需要找到所有可能的异常并相应地处理它。

Answer 2

首先尝试根据您的错误捕获特殊异常，然后针对可能发生的任何其他错误进行常规捕获，check out this和this

  try
   {
         //your code here
    }
   catch (WebException ex)
   {
         MessageBox.Show("No internet available");
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error has occured");
    }

当HttpWebResponse无法连接到服务器/互联网时，如何在c＃中显示消息框

2 个答案: