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Walkthrough: Creating a Margin Glyph


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The latest version of this topic can be found at Walkthrough: Creating a Margin Glyph.

You can customize the appearance of editor margins by using custom editor extensions. This walkthrough puts a custom glyph on the indicator margin whenever the word "todo" appears in a code comment.

Starting in Visual Studio 2015, you do not install the Visual Studio SDK from the download center. It is included as an optional feature in Visual Studio setup. You can also install the VS SDK later on. For more information, see Installing the Visual Studio SDK.

  1. Create a C# VSIX project. (In the New Project dialog, select Visual C# / Extensibility, then VSIX Project.) Name the solution TodoGlyphTest.

  2. Add an Editor Classifier project item. For more information, see Creating an Extension with an Editor Item Template.

  3. Delete the existing class files.

Define a glyph by implementing the IGlyphFactory interface.

To define the glyph

  1. Add a class file and name it TodoGlyphFactory.

  2. Add the following using declarations.

    Imports System.ComponentModel.Composition
    Imports System.Windows
    Imports System.Windows.Shapes
    Imports System.Windows.Media
    Imports System.Windows.Controls
    Imports Microsoft.VisualStudio.Text
    Imports Microsoft.VisualStudio.Text.Editor
    Imports Microsoft.VisualStudio.Text.Formatting
    Imports Microsoft.VisualStudio.Text.Tagging
    Imports Microsoft.VisualStudio.Utilities

  3. Add a class named TodoGlyphFactory that implements IGlyphFactory.

    Friend Class TodoGlyphFactory
        Implements IGlyphFactory

  4. Add a private field that defines the dimensions of the glyph.

        Const m_glyphSize As Double = 16.0

  5. Implement GenerateGlyph by defining the glyph user interface (UI) element. TodoTag is defined later in this walkthrough.

        Public Function GenerateGlyph(ByVal line As IWpfTextViewLine, ByVal tag As IGlyphTag) As System.Windows.UIElement Implements IGlyphFactory.GenerateGlyph
            ' Ensure we can draw a glyph for this marker.
            If tag Is Nothing OrElse Not (TypeOf tag Is TodoTag) Then
                Return Nothing
            End If
            Dim ellipse As Ellipse = New Ellipse()
            ellipse.Fill = Brushes.LightBlue
            ellipse.StrokeThickness = 2
            ellipse.Stroke = Brushes.DarkBlue
            ellipse.Height = m_glyphSize
            ellipse.Width = m_glyphSize
            Return ellipse
        End Function

  6. Add a class named TodoGlyphFactoryProvider that implements IGlyphFactoryProvider. Export this class with a NameAttribute of "TodoGlyph", an OrderAttribute of After VsTextMarker, a ContentTypeAttribute of "code", and a TagTypeAttribute of TodoTag.

        <Export(GetType(IGlyphFactoryProvider)), Name("TodoGlyph"), Order(After:="VsTextMarker"), ContentType("code"), TagType(GetType(TodoTag))>
        Friend NotInheritable Class TodoGlyphFactoryProvider
            Implements IGlyphFactoryProvider

  7. Implement the GetGlyphFactory method by instantiating the TodoGlyphFactory.

            Public Function GetGlyphFactory(ByVal view As IWpfTextView, ByVal margin As IWpfTextViewMargin) As IGlyphFactory Implements IGlyphFactoryProvider.GetGlyphFactory
                Return New TodoGlyphFactory()
            End Function

Define the relationship between the UI element that you defined in the previous steps and the indicator margin by creating a tag type and tagger, and exporting it by using a tagger provider.

To define a todo tag and tagger

  1. Add a new class file to the project and name it TodoTagger.

  2. Add the following imports.

    Imports System
    Imports System.Collections.Generic
    Imports System.ComponentModel.Composition
    Imports Microsoft.VisualStudio.Text
    Imports Microsoft.VisualStudio.Text.Tagging
    Imports Microsoft.VisualStudio.Text.Editor
    Imports Microsoft.VisualStudio.Text.Classification
    Imports Microsoft.VisualStudio.Utilities

  3. Add a class named TodoTag.

    Friend Class TodoTag
        Implements IGlyphTag
        Public Sub New()
        End Sub
    End Class

  4. Modify the class named TodoTagger that implements ITagger<T> of type TodoTag.

    Friend Class TodoTagger
        Implements ITagger(Of TodoTag)

  5. To the TodoTagger class, add private fields for an IClassifier and for the text to find in the classification spans.

        Private m_classifier As IClassifier
        Private Const m_searchText As String = "todo"

  6. Add a constructor that sets the classifier.

        Friend Sub New(ByVal classifier As IClassifier)
            m_classifier = classifier
        End Sub

  7. Implement the GetTags method by finding all the classification spans whose names include the word "comment" and whose text includes the search text. Whenever the search text is found, yield back a new TagSpan<T> of type TodoTag.

        Private Function GetTags(ByVal spans As NormalizedSnapshotSpanCollection) As IEnumerable(Of ITagSpan(Of TodoTag)) Implements ITagger(Of TodoTag).GetTags
            Dim list As List(Of ITagSpan(Of TodoTag))
            list = New List(Of ITagSpan(Of TodoTag))()
            For Each span As SnapshotSpan In spans
                'look at each classification span \
                For Each classification As ClassificationSpan In m_classifier.GetClassificationSpans(span)
                    'if the classification is a comment
                    If classification.ClassificationType.Classification.ToLower().Contains("comment") Then
                        'if the word "todo" is in the comment,
                        'create a new TodoTag TagSpan
                        Dim index As Integer = classification.Span.GetText().ToLower().IndexOf(m_searchText)
                        If index <> -1 Then
                            list.Add(New TagSpan(Of TodoTag)(New SnapshotSpan(classification.Span.Start + index, m_searchText.Length), New TodoTag()))
                        End If
                    End If
                Next classification
            Next span
            Return list
        End Function

  8. Declare a TagsChanged event.

        Public Event TagsChanged(ByVal sender As Object, ByVal e As Microsoft.VisualStudio.Text.SnapshotSpanEventArgs) Implements Microsoft.VisualStudio.Text.Tagging.ITagger(Of TodoTag).TagsChanged

  9. Add a class named TodoTaggerProvider that implements ITaggerProvider, and export it with a ContentTypeAttribute of "code" and a TagTypeAttribute of TodoTag.

    <Export(GetType(ITaggerProvider)), ContentType("code"), TagType(GetType(TodoTag))>
    Friend Class TodoTaggerProvider
        Implements ITaggerProvider

  10. Import the IClassifierAggregatorService.

        Friend AggregatorService As IClassifierAggregatorService

  11. Implement the CreateTagger<T> method by instantiating the TodoTagger.

        Public Function CreateTagger(Of T As Microsoft.VisualStudio.Text.Tagging.ITag)(ByVal buffer As Microsoft.VisualStudio.Text.ITextBuffer) As Microsoft.VisualStudio.Text.Tagging.ITagger(Of T) Implements Microsoft.VisualStudio.Text.Tagging.ITaggerProvider.CreateTagger
            If buffer Is Nothing Then
                Throw New ArgumentNullException("buffer")
            End If
            Return TryCast(New TodoTagger(AggregatorService.GetClassifier(buffer)), ITagger(Of T))
        End Function

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

To build and test the TodoGlyphTest solution

  1. Build the solution.

  2. Run the project by pressing F5. A second instance of Visual Studio is instantiated.

  3. Make sure that the indicator margin is showing. (On the Tools menu, click Options. On the Text Editor page, make sure that Indicator margin is selected.)

  4. Open a code file that has comments. Add the word "todo" to one of the comment sections.

  5. A light blue circle that has a dark blue outline should appear in the indicator margin to the left of the code window.