NullReferenceException in HtmlAgilityPack

c# html-agility-pack

Domanda

Sto cercando di estrarre un link usando xpath dall'url sotto menzionato

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

Il mio codice:

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);
}

Il codice sopra compila bene ma quando provo ad eseguirlo genera un'eccezione

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

Stacktrace completo

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

Quindi, la mia domanda è perché ottengo questa eccezione.

Risposta accettata

Questo è un bug in HtmlAgilityPack. Il documento che stai cercando di analizzare ha <meta http-equiv="Content-Type" content="text/html; charset=iso-utf-8"> dove il valore del charset ( iso-utf-8 ) non può essere analizzato come un nome di codifica valido da AgilityPack. Come ha detto Simon Mourier, questo è un bug introdotto in 1.4.0.0 .

Per evitare ciò, carica manualmente il documento da uno stream e imposta la codifica manualmente in questo modo:

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);
    }
}


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Autorizzato sotto: CC-BY-SA with attribution
Non affiliato con Stack Overflow
È legale questo KB? Sì, impara il perché