XPath select's in HTMLAgilityPack don't work as expected

Question

I'm writing simple screen scraping program in C#, for which i need to select all input's placed inside of one single form named "aspnetForm"(there is 2 forms on the page, and i don't want input's from another), and all inputs in this form placed inside different tables, div's, or just at first-child-level of this form. So i written really simple XPath query: ``` //form[@id='aspnetForm']//input ``` It's works as expected in all browsers that i tested(Chrome, IE, Firefox) - it returns what i want. But in HTMLAgilityPack it's not work at all - SelectNodes just always return NULL. This queries i've written for tests works fine, but returns not what i want. First select all input's that are first-childs for my form, and second just return's form: ``` //form[@id='aspnetForm']/input //form[@id='aspnetForm'] ``` Yes, i know that i can just enumerate over nodes from last query, or make another SelectNodes on it's result, but i don't really want to do this. I want to use same query as in browse…

Accepted Answer

The unexpected behavior in your test occur because the html contains `<form>` element. Here is related discussion :

Ariman : "I've found that after parsing any node does not have any child nodes. All nodes that should be inside the form (, , etc.) are created as it's siblings rather then children.

VikciaR : "In Html specification form tag can overlap, so Htmlagilitypack handle this node a little different..."

[CodePlex discussion : No child nodes for FORM objects ]

And as suggested by VikciaR there, try to modify your test code initialization like this :

```
private static HtmlNode GetHtmlDocumentNode()
{
    var document = new HtmlDocument();
    document.LoadHtml(html);
    
    //execute this line once
    HtmlNode.ElementsFlags.Remove("form");
    
    return document.DocumentNode;
}
```

Side note: `inputQuery` value in test method `TwoSingleLevelXpathsTest()` should be `.//input`. Notice the dot (`.`) at the beginning to indicate that this query is relative to current node. Otherwise it will search from the root, ignoring the former `formQuery` (without the dot, you can change `formQuery` to anything as long as it doesn't return null, the `inputQuery` will always return the same result).

XPath select's in HTMLAgilityPack don't work as expected

Solution

Problem