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