Artikel
11/18/2011

Extensions.Ancestors<T> Method (IEnumerable<T>)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Returns a collection of elements that contains the ancestors of every node in the source collection.

Namespace: System.Xml.Linq
Assembly: System.Xml.Linq (in System.Xml.Linq.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Ancestors(Of T As XNode) ( _
    source As IEnumerable(Of T) _
) As IEnumerable(Of XElement)

public static IEnumerable<XElement> Ancestors<T>(
    this IEnumerable<T> source
)
where T : XNode

Type Parameters

T
The type of the objects in source, constrained to XNode.

Parameters

source
Type: System.Collections.Generic.IEnumerable<T>
An IEnumerable<T> of XNode that contains the source collection.

Return Value

Type: System.Collections.Generic.IEnumerable<XElement>
An IEnumerable<T> of XElement that contains the ancestors of every node in the source collection.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<T>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception	Condition
ArgumentNullException	source is nulla null reference (Nothing in Visual Basic).

Remarks

If multiple nodes in the source collection have the same ancestor, the ancestor will be included multiple times in the result collection. To avoid this, use the Distinct method.

This method uses deferred execution.

Examples

The following example retrieves a collection of the great grandchildren elements. It then uses this axis method to retrieve all ancestors of all elements in the collection.

Dim output As New StringBuilder
Dim xmlTree As XElement = _
    <Root>
        <Child1>
            <GrandChild1>
                <GreatGrandChild1>content</GreatGrandChild1>
            </GrandChild1>
        </Child1>
        <Child2>
            <GrandChild2>
                <GreatGrandChild2>content</GreatGrandChild2>
            </GrandChild2>
        </Child2>
    </Root>

Dim greatGrandChildren = From el In xmlTree.Descendants _
                         Where el.Name.LocalName.StartsWith("Great") _
                         Select el

output.Append("Great Grand Children Elements")
output.Append(Environment.NewLine)
output.Append("----")
output.Append(Environment.NewLine)

For Each de As XElement In greatGrandChildren
    output.Append(de.Name)
    output.Append(Environment.NewLine)
Next

Dim allAncestors = From el In greatGrandChildren.Ancestors.Distinct _
                   Select el

output.Append("")
output.Append(Environment.NewLine)

output.Append("Ancestors")
output.Append(Environment.NewLine)
output.Append("----")
output.Append(Environment.NewLine)

For Each de As XElement In allAncestors
    output.Append(de.Name)
    output.Append(Environment.NewLine)
Next

OutputTextBlock.Text = output.ToString()

StringBuilder output = new StringBuilder();
XElement xmlTree = new XElement("Root",
    new XElement("Child1",
        new XElement("GrandChild1",
            new XElement("GreatGrandChild1", "content")
        )
    ),
    new XElement("Child2",
        new XElement("GrandChild2",
            new XElement("GreatGrandChild2", "content")
        )
    )
);
IEnumerable<XElement> greatGrandChildren =
    from el in xmlTree.Descendants()
    where el.Name.LocalName.StartsWith("Great")
    select el;

output.Append("Great Grand Children Elements" + Environment.NewLine);
output.Append("----" + Environment.NewLine);
foreach (XElement de in greatGrandChildren)
    output.Append(de.Name + Environment.NewLine);

IEnumerable<XElement> allAncestors =
    from el in greatGrandChildren.Ancestors().Distinct()
    select el;

output.Append("" + Environment.NewLine);
output.Append("Ancestors" + Environment.NewLine);
output.Append("----" + Environment.NewLine);
foreach (XElement de in allAncestors)
    output.Append(de.Name + Environment.NewLine);

OutputTextBlock.Text = output.ToString();

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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