Question

I deleted my last, poorly worded question and boiled it down to the simplest form. I am trying to select a root node, but it’s coming back as null.

Here’s my XML

<?xml version="1.0" encoding="UTF-8"?>
<root>
  <children>
    <child>Clark</child>
    <child>Bruce</child>
    <child>Peter</child>
  </children>
</root>

And here’s my code

XmlDocument input = new XmlDocument();
XmlDocument output = new XmlDocument();

input.Load(@"simple.xml");

XmlNode outputNode = output.CreateNode(XmlNodeType.Element, input.ChildNodes[1].Name, null);

Console.WriteLine(outputNode.SelectSingleNode("root") == null ? "null" : "node found"); 
Console.WriteLine(outputNode.SelectSingleNode("/root") == null ? "null" : "node found"); 
Console.WriteLine(outputNode.SelectSingleNode("//root") == null ? "null" : "node found"); 

//After doing this, /root and //root return the root node
output.AppendChild(node);

Console.WriteLine(outputNode.SelectSingleNode("root") == null ? "null" : "node found"); 
Console.WriteLine(outputNode.SelectSingleNode("/root") == null ? "null" : "node found"); 
Console.WriteLine(outputNode.SelectSingleNode("//root") == null ? "null" : "node found"); 

EDIT: @Marc put me on the right track. Actually adding the node to XmlDocument made it work

Answer 1

You have created a new orphan node (i.e. not yet in the tree), without any descendants. It is reasonable that your queries relative to that orphan don’t find anything.

To find existing nodes, look at .DocumentElement, .SelectSingleNode(...) and SelectNodes(...)