How to get all input elements in a form with HtmlAgilityPack without getting a null reference error

c#, html, html-agility-pack, parsing

Solution

You can do the following:

HtmlNode.ElementsFlags.Remove("form");

HtmlDocument doc = new HtmlDocument();

doc.Load(@"D:\test.html");

HtmlNode secondForm = doc.GetElementbyId("form2");

foreach (HtmlNode node in secondForm.Elements("input"))
{
    HtmlAttribute valueAttribute = node.Attributes["value"];

    if (valueAttribute != null)
    {
        Console.WriteLine(valueAttribute.Value);
    }
}

By default HTML Agility Pack parses forms as empty node because they are allowed to overlap other HTML elements. The first line, (`HtmlNode.ElementsFlags.Remove("form");`) disables this behavior allowing you to get the input elements inside the second form.

Update: Example of form elements overlap:

<table>
<form>
<!-- Other elements -->
</table>
</form>

The element begins inside a table but is closed outside the table element. This is allowed in the HTML specification and HTML Agility Pack has to deal with it.

Problem

Example HTML: ``` <html><body> <form id="form1"> <input name="foo1" value="bar1" /> <!-- Other elements --> </form> <form id="form2"> <input name="foo2" value="bar2" /> <!-- Other elements --> </form> </body></html> ``` Test code: ``` HtmlDocument doc = new HtmlDocument(); doc.Load(@"D:\test.html"); foreach (HtmlNode node in doc.GetElementbyId("form2").SelectNodes(".//input")) { Console.WriteLine(node.Attributes["value"].Value); } ``` The statement `doc.GetElementbyId("form2").SelectNodes(".//input")` gives me a null reference. Anything I did wrong? thanks.

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