处理WebClient.DownloadString的正确方法的异常

Question

我想知道在使用时我应该保护自己的例外情况WebClient.DownloadString.

这是我目前正在使用它的方式,但我相信你们可以建议更好的更强大的异常处理.

例如,在我的头顶:

• 没有网络连接.
• 服务器返回404.
• 服务器超时.

处理这些情况并将异常抛出到UI的首选方法是什么？

public IEnumerable<Game> FindUpcomingGamesByPlatform(string platform)
{
    string html;
    using (WebClient client = new WebClient())
    {
        try
        {
            html = client.DownloadString(GetPlatformUrl(platform));
        }
        catch (WebException e)
        {
            //How do I capture this from the UI to show the error in a message box?
            throw e;
        }
    }

    string relevantHtml = "<tr>" + GetHtmlFromThisYear(html);
    string[] separator = new string[] { "<tr>" };
    string[] individualGamesHtml = relevantHtml.Split(separator, StringSplitOptions.None);

    return ParseGames(individualGamesHtml);           
}

Answer 1

如果你抓住WebException,它应该处理大多数情况.WebClient并HttpWebRequest抛出WebException所有HTTP协议错误(4xx和5xx),以及网络级错误(断开连接,主机无法访问等)

如何从UI捕获此信息以在消息框中显示错误？

我不确定我理解你的问题......难道你不能只显示异常消息吗？

MessageBox.Show(e.Message);

不要捕获异常FindUpcomingGamesByPlatform,让它冒泡到调用方法,捕获它并显示消息...

Answer 2

我通常这样处理它以打印远程服务器返回的任何异常消息。鉴于允许用户看到该值。

try
{
    getResult = client.DownloadString(address);
}
catch (WebException ex)
{
    String responseFromServer = ex.Message.ToString() + " ";
    if (ex.Response != null)
    {
        using (WebResponse response = ex.Response)
        {
            Stream dataRs = response.GetResponseStream();
            using (StreamReader reader = new StreamReader(dataRs))
            {
                responseFromServer += reader.ReadToEnd();
            }
        }
    }
    _log.Error("Server Response: " + responseFromServer);
    MessageBox.Show(responseFromServer);
}

Answer 3

我用这个代码:

1. 在这里我init是webclient在加载的事件中

   private void LayoutRoot_Loaded(object sender, RoutedEventArgs e)
   {
     // download from web async
     var client = new WebClient();
     client.DownloadStringCompleted += client_DownloadStringCompleted;
     client.DownloadStringAsync(new Uri("http://whateveraurisingis.com"));
   }
   

2. 回调

   void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
   {
     #region handle download error
     string download = null;
     try
     {
       download = e.Result;
     }
   catch (Exception ex)
     {
       MessageBox.Show(AppMessages.CONNECTION_ERROR_TEXT, AppMessages.CONNECTION_ERROR, MessageBoxButton.OK);
     }
   
     // check if download was successful
     if (download == null)
     {
       return;
     }
     #endregion
   
     // in my example I parse a xml-documend downloaded above      
     // parse downloaded xml-document
     var dataDoc = XDocument.Load(new StringReader(download));
   
     //... your code
   }
   

谢谢.