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Fixed incorrect logic in XmlReader's example (#43799) (#44054)
* Fixed incorrect logic in XmlReader's example (#43799) * Refactor XML streaming example in C# and VB * Format XML string for better readability * Remove unnecessary else statements in XML reader doc --------- Co-authored-by: Andy (Steve) De George <[email protected]>
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‎docs/standard/linq/stream-xml-fragments-xmlreader.md

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Original file line numberDiff line numberDiff line change
@@ -27,163 +27,109 @@ The article [How to perform streaming transform of large XML documents](perform-
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This example creates a custom axis method. You can query it by using a LINQ query. The custom axis method `StreamRootChildDoc` can read a document that has a repeating `Child` element.
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```csharp
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using System.Xml;
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using System.Xml.Linq;
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static IEnumerable<XElement> StreamRootChildDoc(StringReader stringReader)
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{
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using (XmlReader reader = XmlReader.Create(stringReader))
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using XmlReader reader = XmlReader.Create(stringReader);
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reader.MoveToContent();
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// Parse the file and display each of the nodes.
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while (true)
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{
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reader.MoveToContent();
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// Parse the file and display each of the nodes.
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while (reader.Read())
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// If the current node is an element and named "Child"
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if (reader.NodeType == XmlNodeType.Element && reader.Name == "Child")
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{
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switch (reader.NodeType)
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{
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case XmlNodeType.Element:
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if (reader.Name == "Child") {
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XElement el = XElement.ReadFrom(reader) as XElement;
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if (el != null)
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yield return el;
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}
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break;
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}
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// Get the current node and advance the reader to the next
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if (XNode.ReadFrom(reader) is XElement el)
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yield return el;
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}
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else if (!reader.Read())
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break;
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}
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}
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static void Main(string[] args)
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{
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string markup = @"<Root>
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<Child Key=""01"">
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<GrandChild>aaa</GrandChild>
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</Child>
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<Child Key=""02"">
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<GrandChild>bbb</GrandChild>
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</Child>
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<Child Key=""03"">
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<GrandChild>ccc</GrandChild>
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</Child>
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</Root>";
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IEnumerable<string> grandChildData =
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from el in StreamRootChildDoc(new StringReader(markup))
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where (int)el.Attribute("Key") > 1
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select (string)el.Element("GrandChild");
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foreach (string str in grandChildData) {
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Console.WriteLine(str);
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}
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}
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string markup = """
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<Root>
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<Child Key="01">
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<GrandChild>aaa</GrandChild>
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</Child>
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<Child Key="02">
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<GrandChild>bbb</GrandChild>
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</Child>
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<Child Key="03">
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<GrandChild>ccc</GrandChild>
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</Child>
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</Root>
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""";
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IEnumerable<string> grandChildData =
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from el in StreamRootChildDoc(new StringReader(markup))
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where (int)el.Attribute("Key") > 1
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select (string)el.Element("GrandChild");
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foreach (string str in grandChildData)
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Console.WriteLine(str);
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```
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```vb
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Module Module1
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Sub Main()
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Dim markup = "<Root>" &
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" <Child Key=""01"">" &
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" <GrandChild>aaa</GrandChild>" &
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" </Child>" &
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" <Child Key=""02"">" &
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" <GrandChild>bbb</GrandChild>" &
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" </Child>" &
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" <Child Key=""03"">" &
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" <GrandChild>ccc</GrandChild>" &
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" </Child>" &
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"</Root>"
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Dim grandChildData =
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From el In New StreamRootChildDoc(New IO.StringReader(markup))
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Where CInt(el.@Key) > 1
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Select el.<GrandChild>.Value
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For Each s In grandChildData
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Console.WriteLine(s)
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Next
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End Sub
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End Module
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Public Class StreamRootChildDoc
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Implements IEnumerable(Of XElement)
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Imports System.Xml
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Private _stringReader As IO.StringReader
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Public Sub New(ByVal stringReader As IO.StringReader)
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_stringReader = stringReader
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End Sub
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Public Function GetEnumerator() As IEnumerator(Of XElement) Implements IEnumerable(Of XElement).GetEnumerator
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Return New StreamChildEnumerator(_stringReader)
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End Function
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Module Module1
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Public Function GetEnumerator1() As IEnumerator Implements IEnumerable.GetEnumerator
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Return Me.GetEnumerator()
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End Function
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End Class
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Public Iterator Function StreamRootChildDoc(stringReader As IO.StringReader) As IEnumerable(Of XElement)
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Using reader As XmlReader = XmlReader.Create(stringReader)
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reader.MoveToContent()
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Public Class StreamChildEnumerator
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Implements IEnumerator(Of XElement)
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' Parse the file and display each of the nodes.
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While True
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Private _current As XElement
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Private _reader As Xml.XmlReader
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Private _stringReader As IO.StringReader
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' If the current node is an element and named "Child"
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If reader.NodeType = XmlNodeType.Element And reader.Name = "Child" Then
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Public Sub New(ByVal stringReader As IO.StringReader)
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_stringReader = stringReader
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_reader = Xml.XmlReader.Create(_stringReader)
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_reader.MoveToContent()
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End Sub
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' Get the current node and advance the reader to the next
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Dim el As XElement = TryCast(XNode.ReadFrom(reader), XElement)
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Public ReadOnly Property Current As XElement Implements IEnumerator(Of XElement).Current
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Get
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Return _current
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End Get
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End Property
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Public ReadOnly Property Current1 As Object Implements IEnumerator.Current
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Get
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Return Me.Current
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End Get
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End Property
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Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
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While _reader.Read()
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Select Case _reader.NodeType
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Case Xml.XmlNodeType.Element
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Dim el = TryCast(XElement.ReadFrom(_reader), XElement)
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If el IsNot Nothing Then
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_current = el
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Return True
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If (el IsNot Nothing) Then
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Yield el
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End If
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End Select
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End While
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Return False
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ElseIf Not reader.Read() Then
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Exit While
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End If
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End While
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End Using
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End Function
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Public Sub Reset() Implements IEnumerator.Reset
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_reader = Xml.XmlReader.Create(_stringReader)
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_reader.MoveToContent()
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End Sub
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Sub Main()
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#Region "IDisposable Support"
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Dim markup = "<Root>
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<Child Key=""01"">
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<GrandChild>aaa</GrandChild>
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</Child>
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<Child Key=""02"">
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<GrandChild>bbb</GrandChild>
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</Child>
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<Child Key=""03"">
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<GrandChild>ccc</GrandChild>
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</Child>
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</Root>"
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Private disposedValue As Boolean ' To detect redundant calls
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Dim grandChildData =
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From el In StreamRootChildDoc(New IO.StringReader(markup))
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Where CInt(el.@Key) > 1
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Select el.<GrandChild>.Value
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' IDisposable
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Protected Overridable Sub Dispose(ByVal disposing As Boolean)
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If Not Me.disposedValue Then
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If disposing Then
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_reader.Close()
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End If
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End If
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Me.disposedValue = True
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End Sub
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For Each s In grandChildData
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Console.WriteLine(s)
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Next
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Public Sub Dispose() Implements IDisposable.Dispose
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Dispose(True)
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GC.SuppressFinalize(Me)
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End Sub
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#End Region
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End Class
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End Module
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```
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This example produces the following output:

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