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.

Prerequisites

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

Note

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

Creating a Managed Extensibility Framework (MEF) Project

To create a MEF project

1. Create a Visual C# or Visual Basic Editor Classifier project. Name the solution TodoGlyphTest.

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 TodoGlyphTest.dll.

4. Save and close Source.extension.vsixmanifest.

5. Remove 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 imports.

   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
   

   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;
   

3. Add a class named TodoGlyphFactory that implements IGlyphFactory.

   Friend Class TodoGlyphFactory
       Implements IGlyphFactory
   

   internal class TodoGlyphFactory : IGlyphFactory
   

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

   Const m_glyphSize As Double = 16.0
   

   const double m_glyphSize = 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
   

   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;
   }
   

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
   

   [Export(typeof(IGlyphFactoryProvider))]
   [Name("TodoGlyph")]
   [Order(After = "VsTextMarker")]
   [ContentType("code")]
   [TagType(typeof(TodoTag))]
   internal sealed class TodoGlyphFactoryProvider : 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
   

   public IGlyphFactory GetGlyphFactory(IWpfTextView view, IWpfTextViewMargin margin)
   {
       return new TodoGlyphFactory();
   }
   

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 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
   

   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;
   

3. Add a class named TodoTag.

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

   internal class TodoTag : IGlyphTag
   

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

   Friend Class TodoTagger
       Implements ITagger(Of TodoTag)
   

   internal class TodoTagger : ITagger<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"
   

   private IClassifier m_classifier;
   private const string m_searchText = "todo";
   

6. Add a constructor that sets the classifier.

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

   internal TodoTagger(IClassifier classifier)
   {
       m_classifier = classifier;
   }
   

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
   

   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());
                   }
               }
           }
       }
   }
   

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
   

   public event EventHandler<SnapshotSpanEventArgs> 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
   

   [Export(typeof(ITaggerProvider))]
   [ContentType("code")]
   [TagType(typeof(TodoTag))]
   class TodoTaggerProvider : ITaggerProvider
   

10. Import the IClassifierAggregatorService.

    <Import()>
    Friend AggregatorService As IClassifierAggregatorService
    

    [Import]
    internal IClassifierAggregatorService AggregatorService;
    

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
    

    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>;
    }
    

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.