How do I extract specific HTML's part of text using HtmlAgilityPack?

Question

When viewing the page source for a page I use CTRL-F to find all occurrences of "id=", which gives me 82 results. What I want to do is to extract only the numbers after the "id=". For example, if the attribute is id=344 then I only want to get the 344 as string and add it to the List.

The way I'm doing it now I'm not getting links I thought I will get all the links this way and make filter after it but I'm getting empty string and some texts nothing from what I wanted. I guess doing InnerText is wrong.

Source View

idsnumbers = new List<string>();
HtmlWeb hw = new HtmlWeb();
HtmlAgilityPack.HtmlDocument doc = hw.Load("http://www.tapuz.co.il/forums2008/");
foreach (HtmlNode link in doc.DocumentNode.SelectNodes("//a[@href]"))
{
    idsnumbers.Add(link.InnerText);
}

Update getting null exception:

System.NullReferenceException was unhandled
  _HResult=-2147467261
  _message=Object reference not set to an instance of an object.
  HResult=-2147467261
  IsTransient=false
  Message=Object reference not set to an instance of an object.
  Source=WindowsFormsApplication1
  StackTrace:
       at WindowsFormsApplication1.Form1..ctor() in d:\C-Sharp\Tapuz Images\WindowsFormsApplication1\WindowsFormsApplication1\Form1.cs:line 50
       at WindowsFormsApplication1.Program.Main() in d:\C-Sharp\Tapuz Images\WindowsFormsApplication1\WindowsFormsApplication1\Program.cs:line 19
       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.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

torvin · Accepted Answer · 2015-10-05 22:49:31Z

1

You should read ids from the attributes. InnerText is just for the text inside the tag, between the opening and closing brackets. So:

foreach (HtmlNode link in doc.DocumentNode.SelectNodes("//a[@href]"))
{
    idsnumbers.Add(link.Attributes["id"].Value);
}

And if you want to further extract only numbers from ids, you could use RegEx or int.TryParse.

edited Oct 5, 2015 at 22:49

answered Oct 5, 2015 at 22:37

torvin

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2 Comments

Daniel van wolf Over a year ago

torvin i'm getting exception null on the line: idsnumbers.Add(link.Attributes["id"].Value); i added the exception full message to my question.

torvin Over a year ago

If link.Attributes["id"] is null, then your <a> doesn't have it. Just add a null check.

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