Cloning vs. Attaching
When adding XNode (including XElement) or XAttribute objects to a new tree, if the new content has no parent, the objects are simply attached to the XML tree. If the new content already is parented, and is part of another XML tree, the new content is cloned. The newly cloned content is then attached to the XML tree.
Example
The following code demonstrates the behavior when you add a parented element to a tree, and when you add an element with no parent to a tree.
// Create a tree with a child element.
XElement xmlTree1 = new XElement("Root",
new XElement("Child1", 1)
);
// Create an element that is not parented.
XElement child2 = new XElement("Child2", 2);
// Create a tree and add Child1 and Child2 to it.
XElement xmlTree2 = new XElement("Root",
xmlTree1.Element("Child1"),
child2
);
// Compare Child1 identity.
Console.WriteLine("Child1 was {0}",
xmlTree1.Element("Child1") == xmlTree2.Element("Child1") ?
"attached" : "cloned");
// Compare Child2 identity.
Console.WriteLine("Child2 was {0}",
child2 == xmlTree2.Element("Child2") ?
"attached" : "cloned");
' Create a tree with a child element.
Dim xmlTree1 As XElement = _
<Root>
<Child1>1</Child1>
</Root>
' Create an element that is not parented.
Dim child2 As XElement = <Child2>2</Child2>
' Create a tree and add Child1 and Child2 to it.
Dim xmlTree2 As XElement = _
<Root>
<%= xmlTree1.<Child1>(0) %>
<%= child2 %>
</Root>
' Compare Child1 identity.
Console.WriteLine("Child1 was {0}", _
IIf(xmlTree1.Element("Child1") Is xmlTree2.Element("Child1"), _
"attached", "cloned"))
' Compare Child2 identity.
Console.WriteLine("Child2 was {0}", _
IIf(child2 Is xmlTree2.Element("Child2"), _
"attached", "cloned"))
This example produces the following output:
Child1 was cloned
Child2 was attached