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How to: List All Nodes in a Tree

Sometimes it is helpful to list all nodes in a tree. This can be useful when learning exactly how a method or property affects the tree. One approach to listing all nodes in a textual form is to generate an XPath expression that exactly and specifically identifies any node in the tree.

It is not particularly helpful to execute XPath expressions using LINQ to XML. XPath expressions have poorer performance than LINQ to XML queries, and LINQ to XML queries are much more powerful. However, as a way to identify nodes in the XML tree, XPath works well.

Example

This example shows an function named GetXPath that generates a specific XPath expression for any node in the XML tree. It generates appropriate XPath expressions even when nodes are in a namespace. The XPath expressions are generated by using namespace prefixes.

The example then creates a small XML tree that contains an example of several types of nodes. It then iterates through the descendant nodes and prints the XPath expression for each node.

You will notice that the XML declaration is not a node in the tree.

The following is an XML file that contains several types of nodes:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<?target data?>
<Root AttName="An Attribute" xmlns:aw="https://www.adventure-works.com">
  <!--This is a comment-->
  <Child>Text</Child>
  <Child>Other Text</Child>
  <ChildWithMixedContent>text<b>BoldText</b>otherText</ChildWithMixedContent>
  <aw:ElementInNamespace>
    <aw:ChildInNamespace />
  </aw:ElementInNamespace>
</Root>

The following is the list of nodes in the above XML tree, expressed as XPath expressions:

/processing-instruction()
/Root
/Root/@AttName
/Root/@xmlns:aw
/Root/comment()
/Root/Child[1]
/Root/Child[1]/text()
/Root/Child[2]
/Root/Child[2]/text()
/Root/ChildWithMixedContent
/Root/ChildWithMixedContent/text()[1]
/Root/ChildWithMixedContent/b
/Root/ChildWithMixedContent/b/text()
/Root/ChildWithMixedContent/text()[2]
/Root/aw:ElementInNamespace
/Root/aw:ElementInNamespace/aw:ChildInNamespace
public static class MyExtensions
{
    private static string GetQName(XElement xe)
    {
        string prefix = xe.GetPrefixOfNamespace(xe.Name.Namespace);
        if (xe.Name.Namespace == XNamespace.None || prefix == null)
            return xe.Name.LocalName.ToString();
        else
            return prefix + ":" + xe.Name.LocalName.ToString();
    }

    private static string GetQName(XAttribute xa)
    {
        string prefix =
            xa.Parent.GetPrefixOfNamespace(xa.Name.Namespace);
        if (xa.Name.Namespace == XNamespace.None || prefix == null)
            return xa.Name.ToString();
        else
            return prefix + ":" + xa.Name.LocalName;
    }

    private static string NameWithPredicate(XElement el)
    {
        if (el.Parent != null && el.Parent.Elements(el.Name).Count() != 1)
            return GetQName(el) + "[" +
                (el.ElementsBeforeSelf(el.Name).Count() + 1) + "]";
        else
            return GetQName(el);
    }

    public static string StrCat<T>(this IEnumerable<T> source,
        string separator)
    {
        return source.Aggregate(new StringBuilder(),
                   (sb, i) => sb
                       .Append(i.ToString())
                       .Append(separator),
                   s => s.ToString());
    }

    public static string GetXPath(this XObject xobj)
    {
        if (xobj.Parent == null)
        {
            XDocument doc = xobj as XDocument;
            if (doc != null)
                return ".";
            XElement el = xobj as XElement;
            if (el != null)
                return "/" + NameWithPredicate(el);
            // the XPath data model does not include white space text nodes
            // that are children of a document, so this method returns null.
            XText xt = xobj as XText;
            if (xt != null)
                return null;
            XComment com = xobj as XComment;
            if (com != null)
                return
                    "/" +
                    (
                        com
                        .Document
                        .Nodes()
                        .OfType<XComment>()
                        .Count() != 1 ?
                        "comment()[" +
                        (com
                        .NodesBeforeSelf()
                        .OfType<XComment>()
                        .Count() + 1) +
                        "]" :
                        "comment()"
                    );
            XProcessingInstruction pi = xobj as XProcessingInstruction;
            if (pi != null)
                return
                    "/" +
                    (
                        pi.Document.Nodes()
                        .OfType<XProcessingInstruction>()
                        .Count() != 1 ?
                        "processing-instruction()[" +
                        (pi
                        .NodesBeforeSelf()
                        .OfType<XProcessingInstruction>()
                        .Count() + 1) +
                        "]" :
                        "processing-instruction()"
                    );
            return null;
        }
        else
        {
            XElement el = xobj as XElement;
            if (el != null)
            {
                return
                    "/" +
                    el
                    .Ancestors()
                    .InDocumentOrder()
                    .Select(e => NameWithPredicate(e))
                    .StrCat("/") +
                    NameWithPredicate(el);
            }
            XAttribute at = xobj as XAttribute;
            if (at != null)
                return
                    "/" +
                    at
                    .Parent
                    .AncestorsAndSelf()
                    .InDocumentOrder()
                    .Select(e => NameWithPredicate(e))
                    .StrCat("/") +
                    "@" + GetQName(at);
            XComment com = xobj as XComment;
            if (com != null)
                return
                    "/" +
                    com
                    .Parent
                    .AncestorsAndSelf()
                    .InDocumentOrder()
                    .Select(e => NameWithPredicate(e))
                    .StrCat("/") +
                    (
                        com
                        .Parent
                        .Nodes()
                        .OfType<XComment>()
                        .Count() != 1 ?
                        "comment()[" +
                        (com
                        .NodesBeforeSelf()
                        .OfType<XComment>()
                        .Count() + 1) + "]" :
                        "comment()"
                    );
            XCData cd = xobj as XCData;
            if (cd != null)
                return
                    "/" +
                    cd
                    .Parent
                    .AncestorsAndSelf()
                    .InDocumentOrder()
                    .Select(e => NameWithPredicate(e))
                    .StrCat("/") +
                    (
                        cd
                        .Parent
                        .Nodes()
                        .OfType<XText>()
                        .Count() != 1 ?
                        "text()[" +
                        (cd
                        .NodesBeforeSelf()
                        .OfType<XText>()
                        .Count() + 1) + "]" :
                        "text()"
                    );
            XText tx = xobj as XText;
            if (tx != null)
                return
                    "/" +
                    tx
                    .Parent
                    .AncestorsAndSelf()
                    .InDocumentOrder()
                    .Select(e => NameWithPredicate(e))
                    .StrCat("/") +
                    (
                        tx
                        .Parent
                        .Nodes()
                        .OfType<XText>()
                        .Count() != 1 ?
                        "text()[" +
                        (tx
                        .NodesBeforeSelf()
                        .OfType<XText>()
                        .Count() + 1) + "]" :
                        "text()"
                    );
            XProcessingInstruction pi = xobj as XProcessingInstruction;
            if (pi != null)
                return
                    "/" +
                    pi
                    .Parent
                    .AncestorsAndSelf()
                    .InDocumentOrder()
                    .Select(e => NameWithPredicate(e))
                    .StrCat("/") +
                    (
                        pi
                        .Parent
                        .Nodes()
                        .OfType<XProcessingInstruction>()
                        .Count() != 1 ?
                        "processing-instruction()[" +
                        (pi
                        .NodesBeforeSelf()
                        .OfType<XProcessingInstruction>()
                        .Count() + 1) + "]" :
                        "processing-instruction()"
                    );
            return null;
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        XNamespace aw = "https://www.adventure-works.com";
        XDocument doc = new XDocument(
            new XDeclaration("1.0", "utf-8", "yes"),
            new XProcessingInstruction("target", "data"),
            new XElement("Root",
                new XAttribute("AttName", "An Attribute"),
                new XAttribute(XNamespace.Xmlns + "aw", aw.ToString()),
                new XComment("This is a comment"),
                new XElement("Child",
                    new XText("Text")
                ),
                new XElement("Child",
                    new XText("Other Text")
                ),
                new XElement("ChildWithMixedContent",
                    new XText("text"),
                    new XElement("b", "BoldText"),
                    new XText("otherText")
                ),
                new XElement(aw + "ElementInNamespace",
                    new XElement(aw + "ChildInNamespace")
                )
            )
        );
        doc.Save("Test.xml");
        Console.WriteLine(File.ReadAllText("Test.xml"));
        Console.WriteLine("------");
        foreach (XObject obj in doc.DescendantNodes())
        {
            Console.WriteLine(obj.GetXPath());
            XElement el = obj as XElement;
            if (el != null)
                foreach (XAttribute at in el.Attributes())
                    Console.WriteLine(at.GetXPath());
        }
    }
}
Module Module1
<System.Runtime.CompilerServices.Extension()> _
    Private Function StrCat(Of T)(ByVal source As IEnumerable(Of T), _
                                  ByVal separator As String) As String
        Return _
        source.Aggregate(New StringBuilder(), _
            Function(sb, i) sb _
                .Append(i.ToString()) _
                .Append(separator), _
                Function(s) s.ToString())
    End Function

    <System.Runtime.CompilerServices.Extension()> _
    Public Function GetXPath(ByVal xobj As XObject) As String
        Dim retStr As String
        If xobj.Parent Is Nothing Then
            Dim doc As XDocument = TryCast(xobj, XDocument)
            If doc IsNot Nothing Then
                Return "."
            End If
            Dim el As XElement = TryCast(xobj, XElement)
            If el IsNot Nothing Then
                Return ("/" & NameWithPredicate(el))
            End If

            ' The XPath data model does not include white space text nodes
            ' that are children of a document, so this method returns null.
            Dim xt As XText = TryCast(xobj, XText)
            If xt IsNot Nothing Then
                Return Nothing
            End If
            Dim com As XComment = TryCast(xobj, XComment)
            If com IsNot Nothing Then
                If com.Document().Nodes().OfType(Of XComment)().Count() <> 1 Then
                    Return "/comment()[" & (com.NodesBeforeSelf().OfType _
                        (Of XComment)().Count() + 1) & "]"
                Else
                    Return "/comment()"
                End If
            End If

            Dim pi As XProcessingInstruction = TryCast(xobj, XProcessingInstruction)
            If pi IsNot Nothing Then
                If pi.Document.Nodes().OfType(Of XProcessingInstruction)(). _
                        Count() <> 1 Then
                    Return "/processing-instruction()[" & _
                        (pi.NodesBeforeSelf().OfType(Of XProcessingInstruction)() _
                        .Count() + 1) & "]"
                Else
                    Return "/processing-instruction()"
                End If
            End If
        Else
            Dim el As XElement = TryCast(xobj, XElement)
            If el IsNot Nothing Then
                Return "/" & el.Ancestors().InDocumentOrder(). _
                    Select(Function(e) NameWithPredicate(e)) _
                    .StrCat("/") & NameWithPredicate(el)
            End If

            Dim at As XAttribute = TryCast(xobj, XAttribute)
            If at IsNot Nothing Then
                Return "/" & at.Parent().AncestorsAndSelf().InDocumentOrder(). _
                    Select(Function(e) NameWithPredicate(e)).StrCat("/") & _
                    "@" & GetQName(at)
            End If

            Dim com As XComment = TryCast(xobj, XComment)
            If com IsNot Nothing Then
                retStr = "/" & com.Parent.AncestorsAndSelf().InDocumentOrder(). _
                Select(Function(e) NameWithPredicate(e)).StrCat("/") & "comment()"
                If com.Parent().Nodes().OfType(Of XComment)().Count() <> 1 Then
                    retStr &= "[" & (com.NodesBeforeSelf().OfType(Of XComment)().Count() + 1) & "]"
                End If
                Return retStr
            End If

            Dim cd As XCData = TryCast(xobj, XCData)
            If cd IsNot Nothing Then
                retStr = "/" & cd.Parent.AncestorsAndSelf().InDocumentOrder(). _
                    Select(Function(e) NameWithPredicate(e)).StrCat("/") & "text()"
                If cd.Parent.Nodes().OfType(Of XText)().Count() <> 1 Then
                    retStr &= "[" & (cd.NodesBeforeSelf().OfType(Of XText)(). _
                        Count() + 1) & "]"
                End If
                Return retStr
            End If

            Dim tx As XText = TryCast(xobj, XText)
            If tx IsNot Nothing Then
                retStr = "/" & tx.Parent.AncestorsAndSelf().InDocumentOrder(). _
                    Select(Function(e) NameWithPredicate(e)).StrCat("/") & "text()"
                If tx.Parent.Nodes().OfType(Of XText)().Count() <> 1 Then
                    retStr &= "[" & (tx.NodesBeforeSelf().OfType(Of XText)(). _
                        Count() + 1) & "]"
                End If
                Return retStr
            End If

            Dim pi As XProcessingInstruction = TryCast(xobj, XProcessingInstruction)
            If pi IsNot Nothing Then
                retStr = "/" & pi.Parent.AncestorsAndSelf().InDocumentOrder(). _
                    Select(Function(e) NameWithPredicate(e)). _
                    StrCat("/") & "processing-instruction()"
                If pi.Parent.Nodes().OfType(Of XProcessingInstruction)().Count() <> 1 Then
                    retStr &= "[" & (pi.NodesBeforeSelf().OfType(Of XProcessingInstruction)(). _
                        Count() + 1) & "]"
                End If
            End If
        End If
        Return Nothing
    End Function

    Private Function GetQName(ByVal xe As XElement) As String
        Dim prefix As String = xe.GetPrefixOfNamespace(xe.Name.Namespace)
        If xe.Name.Namespace = XNamespace.None Or prefix Is Nothing Then
            Return xe.Name.LocalName.ToString()
        Else
            Return prefix + ":" & xe.Name.LocalName.ToString()
        End If
    End Function

    Private Function GetQName(ByVal xa As XAttribute) As String
        Dim prefix As String = _
            xa.Parent.GetPrefixOfNamespace(xa.Name.Namespace)
        If xa.Name.Namespace = XNamespace.None Or prefix Is Nothing Then
            Return xa.Name.ToString()
        Else
            Return prefix + ":" & xa.Name.LocalName
        End If
    End Function

    Public Function NameWithPredicate(ByVal el As XElement) As String
        If el.Parent IsNot Nothing AndAlso el.Parent.Elements(el.Name).Count() <> 1 Then
            Return GetQName(el) + "[" & _
                (el.ElementsBeforeSelf(el.Name).Count() + 1) & "]"
        Else
            Return GetQName(el)
        End If
    End Function

    Sub Main()
        Dim aw As XNamespace = "https://www.adventure-works.com"
        Dim doc As XDocument = _
            <?xml version='1.0' encoding="utf-8" standalone='yes'?>
            <?target data?>
            <Root AttName='An Attribute' xmlns:aw='https://www.adventure-works.com'>
                <!--This is a comment-->
                <Child>Text</Child>
                <Child>Other Text</Child>
                <ChildWithMixedContent>text<b>BoldText</b>otherText</ChildWithMixedContent>
                <aw:ElementInNamespace>
                    <aw:ChildInNamespace/>
                </aw:ElementInNamespace>
            </Root>
        doc.Save("Test.xml")
        Console.WriteLine(File.ReadAllText("Test.xml"))
        Console.WriteLine("------")
        For Each obj As XObject In doc.DescendantNodes()
            Console.WriteLine(obj.GetXPath())
            Dim el As XElement = TryCast(obj, XElement)
            If el IsNot Nothing Then
                For Each at As XAttribute In el.Attributes()
                    Console.WriteLine(at.GetXPath())
                Next
            End If
        Next
    End Sub
End Module

This example produces the following output:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<?target data?>
<Root AttName="An Attribute" xmlns:aw="https://www.adventure-works.com">
  <!--This is a comment-->
  <Child>Text</Child>
  <Child>Other Text</Child>
  <ChildWithMixedContent>text<b>BoldText</b>otherText</ChildWithMixedContent>
  <aw:ElementInNamespace>
    <aw:ChildInNamespace />
  </aw:ElementInNamespace>
</Root>
------
/processing-instruction()
/Root
/Root/@AttName
/Root/@xmlns:aw
/Root/comment()
/Root/Child[1]
/Root/Child[1]/text()
/Root/Child[2]
/Root/Child[2]/text()
/Root/ChildWithMixedContent
/Root/ChildWithMixedContent/text()[1]
/Root/ChildWithMixedContent/b
/Root/ChildWithMixedContent/b/text()
/Root/ChildWithMixedContent/text()[2]
/Root/aw:ElementInNamespace
/Root/aw:ElementInNamespace/aw:ChildInNamespace

See Also

Concepts

Advanced Query Techniques (LINQ to XML)