HtmlAgilityPack WebGet.Load 给出错误“对象引用未设置为对象的实例”

Question

我正在进行一个关于从经销商网站获取新车价格的项目。我可以获取大多数网站的 html。但是当我尝试加载其中一个时，WebGet.Load(url) 方法给出了Object reference not set to an instance of an object. 错误。我找不到这些网站之间的任何区别。

正常工作的网址示例：

http://www.renault.com.tr/page.aspx?id=1715

http://www.hyundai.com.tr/tr/Content.aspx?id=fiyatlistesi

网站有问题：

http://www.fiat.com.tr/Pages/tr/otomobiller/grandepunto_fiyat.aspx

感谢您的帮助。

var webGet = new HtmlWeb();  
var document = webGet.Load("http://www.fiat.com.tr/Pages/tr/otomobiller/grandepunto_fiyat.aspx");

当我使用这个url文件时没有加载。

Answer 1

实际问题出在 HtmlAgilityPack 内部。页面不工作具有此元内容类型：<META http-equiv="Content-Type" content="text/html; charset=8859-9"> 其中charset=8859-9 似乎不正确。 HAL 内部试图通过使用Encoding.GetEncoding("8859-9") 之类的东西来为这个字符串获取适当的编码，这会引发错误（我认为实际的编码应该是iso-8859-9）。

实际上，您只需要告诉 HAL 不要读取HtmlDocument 的编码（只是HtmlDocument.OptionReadEncoding = true），但HtmlWeb.Load 似乎是不可能的（设置HtmlWeb.AutoDetectEncoding 在这里不起作用）。因此，解决方法可能是手动读取 url（最简单的方法）：

var document = new HtmlDocument();
document.OptionReadEncoding = false;

var url = 
   new Uri("http://www.fiat.com.tr/Pages/tr/otomobiller/grandepunto_fiyat.aspx");
var request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "GET";
using (var response = (HttpWebResponse)request.GetResponse())
{
    using (var stream = response.GetResponseStream())
    {
        document.Load(stream, Encoding.GetEncoding("iso-8859-9"));
    }
}

这有效，并成功解析了页面。

编辑： @:Simon Mourier：是的，它引发了NullReferenceException，因为它捕获了ArgumentException 并在那里设置了_declaredencoding = null。然后_declaredencoding.WindowsCodePage 行抛出空引用。

这是来自 HtmlDocument.cs 的代码块，ReadDocumentEncoding 方法：

try
{
    _declaredencoding = Encoding.GetEncoding(charset);
}
catch (ArgumentException)
{
    _declaredencoding = null;
}
if (_onlyDetectEncoding)
{
    throw new EncodingFoundException(_declaredencoding);
}

if (_streamencoding != null)
{
    if (_declaredencoding.WindowsCodePage != _streamencoding.WindowsCodePage)
    {
        AddError(
            HtmlParseErrorCode.CharsetMismatch,
            _line, _lineposition,
            _index, node.OuterHtml,
            "Encoding mismatch between StreamEncoding: " +
            _streamencoding.WebName + " and DeclaredEncoding: " +
            _declaredencoding.WebName);
    }
}

这是我的堆栈跟踪：

System.NullReferenceException was unhandled
  Message=Object reference not set to an instance of an object.
  Source=HtmlAgilityPack
  StackTrace:
       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.HtmlDocument.Load(Stream stream, Boolean detectEncodingFromByteOrderMarks) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlDocument.cs:line 597
       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 1152
       at HtmlAgilityPack.HtmlWeb.Load(String url) in C:\Source\htmlagilitypack\Trunk\HtmlAgilityPack\HtmlWeb.cs:line 1107
       at test.console.Program.Main(String[] args) in W:\Projects\Me\test.console\test.console\Program.cs:line 54
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: