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Walkthrough: Creating a Margin Glyph

Note

This article applies to Visual Studio 2015. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here

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.

Prerequisites

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.

Creating a MEF Project

  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.

Defining the Glyph

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.

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

    internal class TodoGlyphFactory : IGlyphFactory
    
    Friend Class TodoGlyphFactory
        Implements IGlyphFactory
    
  4. Add a private field that defines the dimensions of the glyph.

    const double m_glyphSize = 16.0;
    
    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 UIElement GenerateGlyph(IWpfTextViewLine line, IGlyphTag tag)
    {
        // Ensure we can draw a glyph for this marker.
        if (tag == null || !(tag is TodoTag))
        {
            return null;
        }
    
        System.Windows.Shapes.Ellipse ellipse = new Ellipse();
        ellipse.Fill = Brushes.LightBlue;
        ellipse.StrokeThickness = 2;
        ellipse.Stroke = Brushes.DarkBlue;
        ellipse.Height = m_glyphSize;
        ellipse.Width = m_glyphSize;
    
        return ellipse;
    }
    
    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(typeof(IGlyphFactoryProvider))]
    [Name("TodoGlyph")]
    [Order(After = "VsTextMarker")]
    [ContentType("code")]
    [TagType(typeof(TodoTag))]
    internal sealed class TodoGlyphFactoryProvider : IGlyphFactoryProvider
    
    <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 IGlyphFactory GetGlyphFactory(IWpfTextView view, IWpfTextViewMargin margin)
    {
        return new TodoGlyphFactory();
    }
    
    Public Function GetGlyphFactory(ByVal view As IWpfTextView, ByVal margin As IWpfTextViewMargin) As IGlyphFactory Implements IGlyphFactoryProvider.GetGlyphFactory
        Return New TodoGlyphFactory()
    End Function
    

Defining a Todo Tag and Tagger

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.

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

    internal class TodoTag : IGlyphTag
    
    Friend Class TodoTag
        Implements IGlyphTag
    
        Public Sub New()
            MyBase.New()
        End Sub
    End Class
    
  4. Modify the class named TodoTagger that implements ITagger<T> of type TodoTag.

    internal class TodoTagger : ITagger<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 IClassifier m_classifier;
    private const string m_searchText = "todo";
    
    Private m_classifier As IClassifier
    Private Const m_searchText As String = "todo"
    
  6. Add a constructor that sets the classifier.

    internal TodoTagger(IClassifier classifier)
    {
        m_classifier = 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.

    IEnumerable<ITagSpan<TodoTag>> ITagger<TodoTag>.GetTags(NormalizedSnapshotSpanCollection spans)
    {
        foreach (SnapshotSpan span in spans)
        {
            //look at each classification span \
            foreach (ClassificationSpan classification in m_classifier.GetClassificationSpans(span))
            {
                //if the classification is a comment
                if (classification.ClassificationType.Classification.ToLower().Contains("comment"))
                {
                    //if the word "todo" is in the comment,
                    //create a new TodoTag TagSpan
                    int index = classification.Span.GetText().ToLower().IndexOf(m_searchText);
                    if (index != -1)
                    {
                        yield return new TagSpan<TodoTag>(new SnapshotSpan(classification.Span.Start + index, m_searchText.Length), new 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 EventHandler<SnapshotSpanEventArgs> TagsChanged;
    
    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(typeof(ITaggerProvider))]
    [ContentType("code")]
    [TagType(typeof(TodoTag))]
    class TodoTaggerProvider : ITaggerProvider
    
    <Export(GetType(ITaggerProvider)), ContentType("code"), TagType(GetType(TodoTag))>
    Friend Class TodoTaggerProvider
        Implements ITaggerProvider
    
  10. Import the IClassifierAggregatorService.

    [Import]
    internal IClassifierAggregatorService AggregatorService;
    
    <Import()>
    Friend AggregatorService As IClassifierAggregatorService
    
  11. Implement the CreateTagger method by instantiating the TodoTagger.

    public ITagger<T> CreateTagger<T>(ITextBuffer buffer) where T : ITag
    {
        if (buffer == null)
        {
            throw new ArgumentNullException("buffer");
        }
    
        return new TodoTagger(AggregatorService.GetClassifier(buffer)) as ITagger<T>;
    }
    
    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
    

Building and Testing the Code

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.