Walkthrough: Outlining

You can implement language-based features such as outlining by defining the kinds of text regions you want to expand or collapse. You can define regions in the context of a language service, or you can define your own file name extension and content type and apply the region definition to only that type, or you can apply the region definitions to an existing content type (such as "text"). This walkthrough shows how to define and display outlining regions.

To complete this walkthrough, you must install the Visual Studio 2010 SDK.


For more information about the Visual Studio SDK, see Visual Studio Integration SDK. To find out how to download the Visual Studio SDK, see Visual Studio Extensibility Developer Center on the MSDN Web site.

To create a MEF project

  1. Create an Editor Classifier project. Name the solution OutlineRegionTest.

  2. Open the source.extension.vsixmanifest file in the VSIX Manifest Editor.

  3. Make sure that the Content heading contains a MEF Component content type and that the Path is set to OutlineRegionTest.dll.

  4. Save and close source.extension.vsixmanifest.

  5. Delete the existing class files.

Outlining regions are marked by a kind of tag (OutliningRegionTag). This tag provides the standard outlining behavior. The outlined region can be expanded or collapsed. The outlined region is marked by a PLUS SIGN if it is collapsed or a MINUS SIGN if it is expanded, and the expanded region is demarcated by a vertical line.

The following steps show how to define a tagger that creates outlining regions for all the regions that are delimited by "[" and "]".

To implement an outlining tagger

  1. Add a class file and name it OutliningTagger.

  2. Import the following namespaces.

    Imports System
    Imports System.Collections.Generic
    Imports System.Linq
    Imports System.Text
    Imports System.ComponentModel.Composition
    Imports Microsoft.VisualStudio.Text.Outlining
    Imports Microsoft.VisualStudio.Text.Tagging
    Imports Microsoft.VisualStudio.Utilities
    Imports Microsoft.VisualStudio.Text
  3. Create a class named OutliningTagger, and have it implement ITagger(Of T):

    Friend NotInheritable Class OutliningTagger
        Implements ITagger(Of IOutliningRegionTag)
  4. Add some fields to track the text buffer and snapshot and to accumulate the sets of lines that should be tagged as outlining regions. This code includes a list of Region objects (to be defined later) that represent the outlining regions.

    'the characters that start the outlining region
    Private startHide As String = "["
    'the characters that end the outlining region
    Private endHide As String = "]"
    'the characters that are displayed when the region is collapsed
    Private ellipsis As String = "..."
    'the contents of the tooltip for the collapsed span
    Private hoverText As String = "hover text"
    Private buffer As ITextBuffer
    Private snapshot As ITextSnapshot
    Private regions As List(Of Region)
  5. Add a tagger constructor that initializes the fields, parses the buffer, and adds an event handler to the Changed event.

    Public Sub New(ByVal buffer As ITextBuffer)
        Me.buffer = buffer
        Me.snapshot = buffer.CurrentSnapshot
        Me.regions = New List(Of Region)()
        AddHandler Me.buffer.Changed, AddressOf BufferChanged
    End Sub
  6. Implement the GetTags method, which instantiates the tag spans. This example assumes that the spans in the NormalizedSpanCollection passed in to the method are contiguous, although this may not always be the case. This method instantiates a new tag span for each of the outlining regions.

    Public Function GetTags(ByVal spans As NormalizedSnapshotSpanCollection) As IEnumerable(Of ITagSpan(Of IOutliningRegionTag)) Implements ITagger(Of Microsoft.VisualStudio.Text.Tagging.IOutliningRegionTag).GetTags
        If spans.Count = 0 Then
            Return Nothing
            Exit Function
        End If
        Dim currentRegions As List(Of Region) = Me.regions
        Dim currentSnapshot As ITextSnapshot = Me.snapshot
        Dim entire As SnapshotSpan = New SnapshotSpan(spans(0).Start, spans(spans.Count - 1).[End]).TranslateTo(currentSnapshot, SpanTrackingMode.EdgeExclusive)
        Dim startLineNumber As Integer = entire.Start.GetContainingLine().LineNumber
        Dim endLineNumber As Integer = entire.[End].GetContainingLine().LineNumber
        Dim list As List(Of ITagSpan(Of IOutliningRegionTag))
        list = New List(Of ITagSpan(Of IOutliningRegionTag))()
        For Each region In currentRegions
            If region.StartLine <= endLineNumber AndAlso region.EndLine >= startLineNumber Then
                Dim startLine = currentSnapshot.GetLineFromLineNumber(region.StartLine)
                Dim endLine = currentSnapshot.GetLineFromLineNumber(region.EndLine)
                'the region starts at the beginning of the "[", and goes until the *end* of the line that contains the "]".
                list.Add(New TagSpan(Of IOutliningRegionTag)(New SnapshotSpan(startLine.Start + region.StartOffset, endLine.End),
                New OutliningRegionTag(False, False, ellipsis, hoverText)))
            End If
        Return list
    End Function
  7. Declare a TagsChanged event handler.

    Public Event TagsChanged As EventHandler(Of SnapshotSpanEventArgs) Implements ITagger(Of IOutliningRegionTag).TagsChanged
  8. Add a BufferChanged event handler that responds to Changed events by parsing the text buffer.

    Private Sub BufferChanged(ByVal sender As Object, ByVal e As TextContentChangedEventArgs)
        ' If this isn't the most up-to-date version of the buffer, then ignore it for now (we'll eventually get another change event).
        If e.After IsNot buffer.CurrentSnapshot Then
            Exit Sub
        End If
    End Sub
  9. Add a method that parses the buffer. The example given here is for illustration only. It synchronously parses the buffer into nested outlining regions.

    Private Sub ReParse()
        Dim newSnapshot As ITextSnapshot = buffer.CurrentSnapshot
        Dim newRegions As New List(Of Region)()
        'keep the current (deepest) partial region, which will have
        ' references to any parent partial regions.
        Dim currentRegion As PartialRegion = Nothing
        For Each line In newSnapshot.Lines
            Dim regionStart As Integer = -1
            Dim text As String = line.GetText()
            'lines that contain a "[" denote the start of a new region.
            If text.IndexOf(startHide, StringComparison.Ordinal) <> -1 Then
                regionStart = text.IndexOf(startHide, StringComparison.Ordinal)
                Dim currentLevel As Integer = If((currentRegion IsNot Nothing), currentRegion.Level, 1)
                Dim newLevel As Integer
                If Not TryGetLevel(text, regionStart, newLevel) Then
                    newLevel = currentLevel + 1
                End If
                'levels are the same and we have an existing region;
                'end the current region and start the next
                If currentLevel = newLevel AndAlso currentRegion IsNot Nothing Then
                    Dim newRegion = New Region()
                    newRegion.Level = currentRegion.Level
                    newRegion.StartLine = currentRegion.StartLine
                    newRegion.StartOffset = currentRegion.StartOffset
                    newRegion.EndLine = line.LineNumber
                    currentRegion = New PartialRegion()
                    currentRegion.Level = newLevel
                    currentRegion.StartLine = line.LineNumber
                    currentRegion.StartOffset = regionStart
                    currentRegion.PartialParent = currentRegion.PartialParent
                    'this is a new (sub)region
                    currentRegion = New PartialRegion()
                    currentRegion.Level = newLevel
                    currentRegion.StartLine = line.LineNumber
                    currentRegion.StartOffset = regionStart
                    currentRegion.PartialParent = currentRegion
                End If
                'lines that contain "]" denote the end of a region
            ElseIf (text.IndexOf(endHide, StringComparison.Ordinal)) <> -1 Then
                regionStart = text.IndexOf(endHide, StringComparison.Ordinal)
                Dim currentLevel As Integer = If((currentRegion IsNot Nothing), currentRegion.Level, 1)
                Dim closingLevel As Integer
                If Not TryGetLevel(text, regionStart, closingLevel) Then
                    closingLevel = currentLevel
                End If
                'the regions match
                If currentRegion IsNot Nothing AndAlso currentLevel = closingLevel Then
                    Dim newRegion As Region
                    newRegion = New Region()
                    newRegion.Level = currentLevel
                    newRegion.StartLine = currentRegion.StartLine
                    newRegion.StartOffset = currentRegion.StartOffset
                    newRegion.EndLine = line.LineNumber
                    currentRegion = currentRegion.PartialParent
                End If
            End If
        'determine the changed span, and send a changed event with the new spans
        Dim oldSpans As New List(Of Span)(Me.regions.[Select](Function(r) AsSnapshotSpan(r, Me.snapshot).TranslateTo(newSnapshot, SpanTrackingMode.EdgeExclusive).Span))
        Dim newSpans As New List(Of Span)(newRegions.[Select](Function(r) AsSnapshotSpan(r, newSnapshot).Span))
        Dim oldSpanCollection As New NormalizedSpanCollection(oldSpans)
        Dim newSpanCollection As New NormalizedSpanCollection(newSpans)
        'the changed regions are regions that appear in one set or the other, but not both.
        Dim removed As NormalizedSpanCollection = NormalizedSpanCollection.Difference(oldSpanCollection, newSpanCollection)
        Dim changeStart As Integer = Integer.MaxValue
        Dim changeEnd As Integer = -1
        If removed.Count > 0 Then
            changeStart = removed(0).Start
            changeEnd = removed(removed.Count - 1).[End]
        End If
        If newSpans.Count > 0 Then
            changeStart = Math.Min(changeStart, newSpans(0).Start)
            changeEnd = Math.Max(changeEnd, newSpans(newSpans.Count - 1).[End])
        End If
        Me.snapshot = newSnapshot
        Me.regions = newRegions
        If changeStart <= changeEnd Then
            Dim snap As ITextSnapshot = Me.snapshot
            RaiseEvent TagsChanged(Me, New SnapshotSpanEventArgs(New SnapshotSpan(Me.snapshot, Span.FromBounds(changeStart, changeEnd))))
        End If
    End Sub
  10. The following helper method gets an integer that represents the level of the outlining, such that 1 is the leftmost brace pair.

    Private Shared Function TryGetLevel(ByVal text As String, ByVal startIndex As Integer, ByRef level As Integer) As Boolean
        level = -1
        If text.Length > startIndex + 3 Then
            If Integer.TryParse(text.Substring(startIndex + 1), level) Then
                Return True
            End If
        End If
        Return False
    End Function
  11. The following helper method translates a Region (defined later in this topic) into a SnapshotSpan.

    Private Shared Function AsSnapshotSpan(ByVal region As Region, ByVal snapshot As ITextSnapshot) As SnapshotSpan
        Dim startLine = snapshot.GetLineFromLineNumber(region.StartLine)
        Dim endLine = If((region.StartLine = region.EndLine), startLine, snapshot.GetLineFromLineNumber(region.EndLine))
        Return New SnapshotSpan(startLine.Start + region.StartOffset, endLine.[End])
    End Function
  12. The following code is for illustration only. It defines a PartialRegion class that contains the line number and offset of the start of an outlining region, and also a reference to the parent region (if any). This enables the parser to set up nested outlining regions. A derived Region class contains a reference to the line number of the end of an outlining region.

    Private Class PartialRegion
        Private _StartLine As Integer
        Public Property StartLine() As Integer
                Return _StartLine
            End Get
            Set(ByVal value As Integer)
                _StartLine = value
            End Set
        End Property
        Private _StartOffset As Integer
        Public Property StartOffset() As Integer
                Return _StartOffset
            End Get
            Set(ByVal value As Integer)
                _StartOffset = value
            End Set
        End Property
        Private _Level As Integer
        Public Property Level() As Integer
                Return _Level
            End Get
            Set(ByVal value As Integer)
                _Level = value
            End Set
        End Property
        Private _PartialParent As PartialRegion
        Public Property PartialParent() As PartialRegion
                Return _PartialParent
            End Get
            Set(ByVal value As PartialRegion)
                _PartialParent = value
            End Set
        End Property
    End Class
    Private Class Region
        Inherits PartialRegion
        Private _EndLine As Integer
        Public Property EndLine() As Integer
                Return _EndLine
            End Get
            Set(ByVal value As Integer)
                _EndLine = value
            End Set
        End Property
    End Class

You must export a tagger provider for your tagger. The tagger provider creates an OutliningTagger for a buffer of the "text" content type, or else returns an OutliningTagger if the buffer already has one.

To implement a tagger provider

  1. Create a class named OutliningTaggerProvider that implements ITaggerProvider, and export it with the ContentType and TagType attributes.

    <Export(GetType(ITaggerProvider))> _
    <TagType(GetType(IOutliningRegionTag))> _
    <ContentType("text")> _
    Friend NotInheritable Class OutliningTaggerProvider
        Implements ITaggerProvider
  2. Implement the CreateTagger(Of T) method by adding an OutliningTagger to the properties of the buffer.

    Public Function CreateTagger(Of T As ITag)(ByVal buffer As ITextBuffer) As ITagger(Of T) Implements ITaggerProvider.CreateTagger
        'create a single tagger for each buffer.
        Dim sc As Func(Of ITagger(Of T)) = Function() TryCast(New OutliningTagger(buffer), ITagger(Of T))
        Return buffer.Properties.GetOrCreateSingletonProperty(Of ITagger(Of T))(sc)
    End Function

To test this code, build the OutlineRegionTest solution and run it in the experimental instance.

To build and test the OutlineRegionTest solution

  1. Build the solution.

  2. When you run this project in the debugger, a second instance of Visual Studio is instantiated.

  3. Create a text file. Type some text that includes both the opening brace and the closing brace.

  4. There should be an outlining region that includes both braces. You should be able to click the MINUS SIGN to the left of the open brace to collapse the outlining region. When the region is collapsed, the ellipsis symbol (...) should appear to the left of the collapsed region, and a popup containing the text hover text should appear when you move the pointer over the ellipsis.

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