NullReferenceException in HtmlAgilityPack

本文关键字：HtmlAgilityPack in NullReferenceException | 更新日期: 2023-09-27 18:31:10

我正在尝试使用下面提到的网址中的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);
}

上面的代码编译良好，但是当我尝试运行时，它会生成异常

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

完整的堆栈跟踪

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会出现这个异常。

NullReferenceException in HtmlAgilityPack

这是

HtmlAgilityPack中的一个错误。您尝试解析的文档<meta http-equiv="Content-Type" content="text/html; charset=iso-utf-8"> AgilityPack 无法将charset值 （ iso-utf-8 ） 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。

为避免这种情况，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);
    }
}
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