C# Null Exception using HTML Agility Pack

Question

I have a function where I am trying to get some text from this webpage:

http://www.nla.gd/winning-numbers/

public static string get_webpage(string url)
{
    HtmlWeb web = new HtmlWeb();
    HtmlDocument doc = web.Load(url);
    string date = doc.DocumentNode.InnerText;
    string lotto_winning_numbers = doc.DocumentNode.SelectNodes("//[@id=\"main\"]/div/strong/div/div[2]/div[1]/div[1]").ToString();

    return lotto_winning_numbers;
}

When I run the function I get a NULL Exception.

Is my xpath correct?

Additionally, you are calling `ToString()` on a collection. So the output will be the type name of the collection, not any of the contents. — Keith Payne, Oct 28 '14 at 14:20
Note: using any variation of "getting NullRef exception" as title is almost automatic duplicate of http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it. Please avoid such titles in the future. — Alexei Levenkov, Oct 28 '14 at 14:24
Please show me the error in the xpath or somewhere to learn xpath? — Dami1, Oct 28 '14 at 14:28
I am trying to capture 2,3,9,24,29 from that page but my code comes up null? — Dami1, Oct 28 '14 at 20:40

Alexei Levenkov · Accepted Answer · 2014-10-28T14:57:09.943

1

You can't have filter by itself in XPath (like [@id='main']). You need to apply filter to collection of nodes like div or *.

Note that you also want to combine values elements in resulting collection, not convert collection itself to string.

Something like:

// Note "*" in front of filter
var lotto_winning_numbers = doc.DocumentNode.SelectNodes(
       "//*[@id=\"main\"]/div/strong/div/div[2]/div[1]/div[1]");

// lotto_winning_numbers is collection of nodes here.
return lotto_winning_numbers == null ? String.Empty : 
       String.Join(", ", lotto_winning_numbers);

Check MSDN article XPath Examples or many other tutorials to learn more.

edited Oct 28 '14 at 14:57

answered Oct 28 '14 at 14:28

Alexei Levenkov

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Please give me a little more detail cause I am not seeing the error. – Dami1 Oct 28 '14 at 14:40
@Dami1 what details you are looking for? Like the one in the sample "Note "*" in front of condition"? – Alexei Levenkov Oct 28 '14 at 14:41
Should I remove it is there somewhere I can get the syntax for xpath? – Dami1 Oct 28 '14 at 14:50
I see you meant Not but you wrote note. – Dami1 Oct 28 '14 at 14:52
@Dami1 - I've updated answer with more correct term ("filter" instead of "condition") so you should be able to find articles about filtering in XPath (also [condition in XPath](http://www.bing.com/search?q=condition+in+XPath) is reasonable search term too). – Alexei Levenkov Oct 28 '14 at 15:00
It's not retrieving the data? – Dami1 Oct 28 '14 at 20:48

C# Null Exception using HTML Agility Pack

1 Answers1