XPathNavigator::Select Method (XPathExpression^)
Selects a node set using the specified XPathExpression.
Assembly: System.Xml (in System.Xml.dll)
Parameters
- expr
-
Type:
System.Xml.XPath::XPathExpression^
An XPathExpression object containing the compiled XPath query.
Return Value
Type: System.Xml.XPath::XPathNodeIterator^An XPathNodeIterator that points to the selected node set.
| Exception | Condition |
|---|---|
| ArgumentException | The XPath expression contains an error or its return type is not a node set. |
| XPathException | The XPath expression is not valid. |
The context for the selection is the position of the XPathNavigator when you called this method. After you call this method, the XPathNodeIterator returned represents the set of selected nodes. Use MoveNext on the XPathNodeIterator to iterate over the selected node set.
The following C# code iterates over the selected set of nodes.
XPathNodeIterator ni = nav.Select(expr);
while (ni.MoveNext())
{
Console.WriteLine(ni.Current.Name);
}
The following are important notes to consider when using the Select method.
You can still use any of the XPathNavigator object's navigation methods to move within the XPathNavigator. The XPathNavigator navigation methods are independent of the selected nodes in the XPathNodeIterator.
Future calls to the Select method return a new XPathNodeIterator object that points to the selected set of nodes that matches the new Select call. The two XPathNodeIterator objects are completely independent of each other.
If the XPathExpression requires namespace resolution, the prefix and namespace URI pair must be added to an XmlNamespaceManager, and the SetContext method must be called to specify the XmlNamespaceManager to use for namespace resolution.
For example, suppose the document contains the following XML nodes.
<bookstore xmlns:bk='urn:samples'>
<book bk:ISBN='1-325-0980'>
<title>Pride And Prejudice</title>
</book>
</bookstore>
In this case, the following C# code selects the bk:ISBN node.
XPathExpression expr = nav.Compile("book/@bk:ISBN");
XmlNamespaceManager mngr = new XmlNamespaceManager(new NameTable());
mngr.AddNamespace("bk","urn:samples");
expr.SetContext(mngr);
XPathNodeIterator ni = nav.Select(expr);
Note |
|---|
If the XPathExpression does not include a prefix, it is assumed that the namespace URI is the empty namespace. If your XML includes a default namespace, you must still use the SetContext method and provide an XmlNamespaceManager that contains a prefix and namespace URI to handle the default namespace. |
For example, suppose you have the following XML.
<bookstore xmlns="http://www.lucernepublishing.com">
<book>
<title>Pride And Prejudice</title>
</book>
</bookstore>
In this case, the following C# code selects all book nodes:
XmlNamespaceManager nsmgr = new XmlNamespaceManager(nav.NameTable);
nsmgr.AddNamespace("ab", "http://www.lucernepublishing.com");
XPathExpression expr;
expr = nav.Compile("//ab:book");
expr.SetContext(nsmgr);
XPathNodeIterator ni = nav.Select(expr);
This method has no effect on the state of the XPathNavigator.
The following example uses the Select method to select a node set.
XPathDocument^ document = gcnew XPathDocument("books.xml");
XPathNavigator^ navigator = document->CreateNavigator();
XPathExpression^ query = navigator->Compile("/bookstore/book");
XPathNodeIterator^ nodes = navigator->Select(query);
XPathNavigator^ nodesNavigator = nodes->Current;
XPathNodeIterator^ nodesText = nodesNavigator->SelectDescendants(XPathNodeType::Text, false);
while (nodesText->MoveNext())
{
Console::WriteLine(nodesText->Current->Value);
}
The example takes the books.xml file as an input.
<?xml version="1.0" encoding="utf-8" ?> <bookstore> <book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0"> <title>The Autobiography of Benjamin Franklin</title> <author> <first-name>Benjamin</first-name> <last-name>Franklin</last-name> </author> <price>8.99</price> </book> <book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2"> <title>The Confidence Man</title> <author> <first-name>Herman</first-name> <last-name>Melville</last-name> </author> <price>11.99</price> </book> <book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6"> <title>The Gorgias</title> <author> <name>Plato</name> </author> <price>9.99</price> </book> </bookstore>
Available since 1.1
Silverlight
Available since 4.0
