递归函数最初使用’outer’XmlWriter,写入缩进的XML,直到它看到TextBlock元素.当它遇到TextBlock元素时,它创建’inner’XmlWriter对象,将TextBlock元素的子元素写入它.它还将空格写入“内部”XmlWriter.

当写入TextBlock元素的“内部”XmlWriter对象完成时,写入器写入的文本将使用WriteRaw方法写入“外部”XmlWriter.

这种方法的优点是没有对XML进行后处理.后处理XML是非常困难的,并确保您已正确处理所有案例,包括CData节点中的任意文本等.所有XML仅使用XmlWriter类编写,从而确保始终写入有效的XML .唯一的例外是使用WriteRaw方法编写的特制白色空间,可实现所需的缩进行为.

一个关键点是“内部”XmlWriter对象的一致性级别设置为ConformanceLevel.Fragment,因为“内部”XmlWriter需要编写没有根元素的XML.

为了实现Run元素所需的格式化(即相邻的Run元素在它们之间没有无关紧要的空格),代码使用GroupAdjacent扩展方法.前段时间,我在the GroupAdjacent extension method for VB写了一篇博文.

当您使用指定的示例XML运行代码时,它会输出：

<Canvas>
  <Grid>
    <TextBlock>
      <Run Text="r" /><Run Text="u" /><Run Text="n" />
    </TextBlock>
    <TextBlock>
      <Run Text="far a" /><Run Text="way" /><Run Text=" from me" />
    </TextBlock>
  </Grid>
  <Grid>
    <TextBlock>
      <Run Text="I" /><Run Text=" " /><Run Text="want" />
      <LineBreak />
    </TextBlock>
    <TextBlock>
      <LineBreak />
      <Run Text="...thi" /><Run Text="s to" />
      <LineBreak />
      <Run Text=" work" />
    </TextBlock>
  </Grid>
</Canvas>

以下是VB.NET示例程序的完整列表.另外,我写了一篇博客文章Custom Formatting of XML using LINQ to XML,它提供了等效的C#代码.

`

Imports System.Text
Imports System.Xml

Public Class GroupOfAdjacent(Of TElement,TKey)
    Implements IEnumerable(Of TElement)

    Private _key As TKey
    Private _groupList As List(Of TElement)

    Public Property GroupList() As List(Of TElement)
        Get
            Return _groupList
        End Get
        Set(ByVal value As List(Of TElement))
            _groupList = value
        End Set
    End Property

    Public ReadOnly Property Key() As TKey
        Get
            Return _key
        End Get
    End Property

    Public Function GetEnumerator() As System.Collections.Generic.IEnumerator(Of TElement) _
            Implements System.Collections.Generic.IEnumerable(Of TElement).GetEnumerator
        Return _groupList.GetEnumerator
    End Function

    Public Function GetEnumerator1() As System.Collections.IEnumerator _
            Implements System.Collections.IEnumerable.GetEnumerator
        Return _groupList.GetEnumerator
    End Function

    Public Sub New(ByVal key As TKey)
        _key = key
        _groupList = New List(Of TElement)
    End Sub
End Class

Module Module1
    <System.Runtime.CompilerServices.Extension()> _
    Public Function GroupAdjacent(Of TElement,TKey)(ByVal source As IEnumerable(Of TElement),_
                ByVal keySelector As Func(Of TElement,TKey)) As List(Of GroupOfAdjacent(Of TElement,TKey))
        Dim lastKey As TKey = Nothing
        Dim currentGroup As GroupOfAdjacent(Of TElement,TKey) = Nothing
        Dim allGroups As List(Of GroupOfAdjacent(Of TElement,TKey)) = New List(Of GroupOfAdjacent(Of TElement,TKey))()
        For Each item In source
            Dim thisKey As TKey = keySelector(item)
            If lastKey IsNot Nothing And Not thisKey.Equals(lastKey) Then
                allGroups.Add(currentGroup)
            End If
            If Not thisKey.Equals(lastKey) Then
                currentGroup = New GroupOfAdjacent(Of TElement,TKey)(keySelector(item))
            End If
            currentGroup.GroupList.Add(item)
            lastKey = thisKey
        Next
        If lastKey IsNot Nothing Then
            allGroups.Add(currentGroup)
        End If
        Return allGroups
    End Function

    Public Sub WriteStartElement(ByVal writer As XmlWriter,ByVal e As XElement)
        Dim ns As XNamespace = e.Name.Namespace
        writer.WriteStartElement(e.GetPrefixOfNamespace(ns),_
            e.Name.LocalName,ns.NamespaceName)
        For Each a In e.Attributes
            ns = a.Name.Namespace
            Dim localName As String = a.Name.LocalName
            Dim namespaceName As String = ns.NamespaceName
            writer.WriteAttributeString( _
                e.GetPrefixOfNamespace(ns),_
                localName,_
                IIf(namespaceName.Length = 0 And localName = "xmlns",_
                    XNamespace.Xmlns.NamespaceName,namespaceName),a.Value)
        Next
    End Sub

    Public Sub WriteElement(ByVal writer As XmlWriter,ByVal e As XElement)
        If (e.Name = "TextBlock") Then
            WriteStartElement(writer,e)
            writer.WriteRaw(Environment.NewLine)

            ' Create an XML writer that outputs no insignificant white space so that we can
            ' write to it and explicitly control white space.
            Dim settings As XmlWriterSettings = New XmlWriterSettings()
            settings.Indent = False
            settings.OmitXmlDeclaration = True
            settings.ConformanceLevel = ConformanceLevel.Fragment
            Dim sb As StringBuilder = New StringBuilder()
            Using newXmlWriter As XmlWriter = XmlWriter.Create(sb,settings)
                ' Group adjacent runs so that they can be output with no whitespace between them
                Dim groupedRuns = e.Nodes().GroupAdjacent( _
                    Function(n) As Boolean?
                        If TypeOf n Is XElement Then
                            Dim element As XElement = n
                            If element.Name = "Run" Then
                                Return True
                            End If
                            Return False
                        End If
                        Return False
                    End Function)
                For Each g In groupedRuns
                    If g.Key = True Then
                        ' Write white space so that the line of Run elements is properly indented.
                        newXmlWriter.WriteRaw("".PadRight((e.Ancestors().Count() + 1) * 2))
                        For Each run In g
                            run.WriteTo(newXmlWriter)
                        Next
                        newXmlWriter.WriteRaw(Environment.NewLine)
                    Else
                        For Each g2 In g
                            ' Write some white space so that each child element is properly indented.
                            newXmlWriter.WriteRaw("".PadRight((e.Ancestors().Count() + 1) * 2))
                            g2.WriteTo(newXmlWriter)
                            newXmlWriter.WriteRaw(Environment.NewLine)
                        Next
                    End If
                Next
            End Using
            writer.WriteRaw(sb.ToString())
            writer.WriteRaw("".PadRight(e.Ancestors().Count() * 2))
            writer.WriteEndElement()
        Else
            WriteStartElement(writer,e)
            For Each n In e.Nodes
                If TypeOf n Is XElement Then
                    Dim element = n
                    WriteElement(writer,element)
                    Continue For
                End If
                n.WriteTo(writer)
            Next
            writer.WriteEndElement()
        End If
    End Sub

    Function ToStringWithCustomWhiteSpace(ByVal element As XElement) As String
        ' Create XmlWriter that indents.
        Dim settings As XmlWriterSettings = New XmlWriterSettings()
        settings.Indent = True
        settings.OmitXmlDeclaration = True
        Dim sb As StringBuilder = New StringBuilder()
        Using xmlWriter As XmlWriter = xmlWriter.Create(sb,settings)
            WriteElement(xmlWriter,element)
        End Using
        Return sb.ToString()
    End Function

    Sub Main()
        Dim myXML As XElement = _
            <Canvas>
                <Grid>
                    <TextBlock>
                        <Run Text='r'/>
                        <Run Text='u'/>
                        <Run Text='n'/>
                    </TextBlock>
                    <TextBlock>
                        <Run Text='far a'/>
                        <Run Text='way'/>
                        <Run Text=' from me'/>
                    </TextBlock>
                </Grid>
                <Grid>
                    <TextBlock>
                        <Run Text='I'/>
                        <Run Text=' '/>
                        <Run Text='want'/>
                        <LineBreak/>
                    </TextBlock>
                    <TextBlock>
                        <LineBreak/>
                        <Run Text='...thi'/>
                        <Run Text='s to'/>
                        <LineBreak/>
                        <Run Text=' work'/>
                    </TextBlock>
                </Grid>
            </Canvas>
        Console.Write(ToStringWithCustomWhiteSpace(myXML))
        Console.ReadLine()
    End Sub

End Module

`