Question

我正在开展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HTML。但是当我尝试加载其中一个时，WebGet.Load（url）方法会出现Object reference not set to an instance of an object.错误。我发现这些网站之间没有任何差异。

正常工作网址示例：

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");

当我使用此url文档时未加载。

Answer 1

实际问题出在HtmlAgilityPack内部。页面无法使用此元内容类型：<META http-equiv="Content-Type" content="text/html; charset=8859-9">其中charset=8859-9似乎是不正确的。 HAL内部尝试通过使用类似Encoding.GetEncoding("8859-9")的内容来为此字符串获取适当的编码，这会引发错误（我认为实际编码应为iso-8859-9）。

实际上，您只需告诉HAL不要读取HtmlDocument的编码（仅HtmlDocument.OptionReadEncoding = true），但HtmlWeb.Load似乎无法做到这一点（设置为HtmlWeb.AutoDetectEncoding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"));
    }
}

这样做，并成功解析页面。

编辑： @：Simon Mourier：是的，它会引发NullReferenceException，因为它会抓住ArgumentException并在那里设置_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:

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

1 个答案: