HtmlAgilityPack中的NullReferenceException

我试图从下面提到的URL使用xpath提取link

 string url = "http://www.album-cover-art.org/search.php?q=Ruin+-+Live+Album+Version+Lamb+of+God" 

我的代码：

 HtmlAgilityPack.HtmlWeb web = new HtmlAgilityPack.HtmlWeb(); HtmlAgilityPack.HtmlDocument htmlDoc = new HtmlAgilityPack.HtmlDocument(); htmlDoc = web.Load(url); //Exception generated here Line 23 if (htmlDoc.DocumentNode != null) { HtmlNode linkNode = htmlDoc.DocumentNode.SelectSingleNode(".//*[@id='related_search_row']/img/@src"); if (linkNode != null) Console.WriteLine(linkNode.InnerText); } 

上面的代码编译得很好，但是当我尝试运行它时会产生exception

 Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object. 

完成堆栈跟踪

 System.NullReferenceException: Object reference not set to an instance of an object. at HtmlAgilityPack.HtmlDocument.ReadDocumentEncoding(HtmlNode node) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlDocument.cs:line 1916 at HtmlAgilityPack.HtmlDocument.PushNodeEnd(Int32 index, Boolean close) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlDocument.cs:line 1805 at HtmlAgilityPack.HtmlDocument.Parse() in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlDocument.cs:line 1468 at HtmlAgilityPack.HtmlDocument.Load(TextReader reader) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlDocument.cs:line 769 at HtmlAgilityPack.HtmlWeb.Get(Uri uri, String method, String path, HtmlDocument doc, IWebProxy proxy, ICredentials creds) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlWeb.cs:line 1515 at HtmlAgilityPack.HtmlWeb.LoadUrl(Uri uri, String method, WebProxy proxy, NetworkCredential creds) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlWeb.cs:line 1563 at HtmlAgilityPack.HtmlWeb.Load(String url, String method) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlWeb.cs:line 1149 at HtmlAgilityPack.HtmlWeb.Load(String url) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlWeb.cs:line 1107 at ScreenScrapping.Program.Main(String[] args) in c:\Users\ranveer\csharp\ScreenScrapping\ScreenScrapping\Program.cs:line 23 

所以，我的问题是为什么我得到这个例外。

Answer 1

这是HtmlAgilityPack中的一个错误。 您尝试解析的文档有其中charset值（ iso-utf-8 ）不能被AgilityPack解析为有效的编码名称。 正如Simon Mourier 所说 ， 这是1.4.0.0中引入的错误 。

要避免这种情况，请从流中手动加载文档并手动设置编码，如下所示：

 var htmlDoc = new HtmlDocument(); htmlDoc.OptionReadEncoding = false; var request = (HttpWebRequest)WebRequest.Create(url); request.Method = "GET"; using (var response = (HttpWebResponse)request.GetResponse()) { using (var stream = response.GetResponseStream()) { htmlDoc.Load(stream, Encoding.UTF8); } }