XmlNode::SelectSingleNode Method (String^)
Selects the first XmlNode that matches the XPath expression.
Assembly: System.Xml (in System.Xml.dll)
Parameters
- xpath
-
Type:
System::String^
The XPath expression. See XPath Examples.
Return Value
Type: System.Xml::XmlNode^The first XmlNode that matches the XPath query or null if no matching node is found.
| Exception | Condition |
|---|---|
| XPathException | The XPath expression contains a prefix. |
If the XPath expression requires namespace resolution, you must use the SelectSingleNode overload which takes an XmlNamespaceManager as its argument. The XmlNamespaceManager is used to resolve namespaces.
Note |
|---|
If the XPath expression 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 XmlNamespaceManager and add a prefix and namespace URI to it; otherwise, you will not get a selected node. For more information, see Select Nodes Using XPath Navigation. |
Note |
|---|
A common issue when formulating XPath expressions is how to include a single quote (') or double quote (") in the expression. If you have to search for a value that includes a single quote, you must enclose the string in double quotes. If you need to search for a value that includes a double quote, you must enclose the string in single quotes. |
For example, suppose you have the following XML:
<bookstore>
<book>
<title>'Emma'</title>
</book>
</bookstore>
The following Visual Basic code selects an element that contains single quotes:
book = root.SelectSingleNode("descendant::book[title=""'Emma'""]")
This method is a Microsoft extension to the Document Object Model (DOM).
The following example changes the price of the first Jane Austen book.
#using <System.Xml.dll> using namespace System; using namespace System::IO; using namespace System::Xml; int main() { XmlDocument^ doc = gcnew XmlDocument; doc->Load( "booksort.xml" ); XmlNode^ book; XmlNode^ root = doc->DocumentElement; book = root->SelectSingleNode( "descendant::book[author/last-name='Austen']" ); //Change the price on the book. book->LastChild->InnerText = "15.95"; Console::WriteLine( "Display the modified XML document...." ); doc->Save( Console::Out ); }
The example uses the file, booksort.xml, as input.
<?xml version="1.0"?> <!-- A fragment of a book store inventory database --> <bookstore xmlns:bk="urn:samples"> <book genre="novel" publicationdate="1997" bk:ISBN="1-861001-57-8"> <title>Pride And Prejudice</title> <author> <first-name>Jane</first-name> <last-name>Austen</last-name> </author> <price>24.95</price> </book> <book genre="novel" publicationdate="1992" bk:ISBN="1-861002-30-1"> <title>The Handmaid's Tale</title> <author> <first-name>Margaret</first-name> <last-name>Atwood</last-name> </author> <price>29.95</price> </book> <book genre="novel" publicationdate="1991" bk:ISBN="1-861001-57-6"> <title>Emma</title> <author> <first-name>Jane</first-name> <last-name>Austen</last-name> </author> <price>19.95</price> </book> <book genre="novel" publicationdate="1982" bk:ISBN="1-861001-45-3"> <title>Sense and Sensibility</title> <author> <first-name>Jane</first-name> <last-name>Austen</last-name> </author> <price>19.95</price> </book> </bookstore>
Available since 1.1
