Walkthrough: Creating a Margin Glyph

Article
03/07/2013

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 2012 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

Create a Visual C# or Visual Basic Editor Classifier project. Name the solution TodoGlyphTest.
Open the Source.extension.vsixmanifest file in the VSIX Manifest Editor.
Make sure that the Content heading contains a MEF Component content type and that the Path is set to TodoGlyphTest.dll.
Save and close Source.extension.vsixmanifest.
Remove the existing class files.

Defining the Glyph

Define a glyph by implementing the IGlyphFactory interface.

To define the glyph

Add a class file and name it TodoGlyphFactory.

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;

Add a class named TodoGlyphFactory that implements IGlyphFactory.

Friend Class TodoGlyphFactory
    Implements IGlyphFactory

internal class TodoGlyphFactory : IGlyphFactory

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

Const m_glyphSize As Double = 16.0

const double m_glyphSize = 16.0;

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;
}

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

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

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

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;

Add a class named TodoTag.

Friend Class TodoTag
    Implements IGlyphTag

    Public Sub New()
        MyBase.New()
    End Sub 
End Class

internal class TodoTag : IGlyphTag

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

Friend Class TodoTagger
    Implements ITagger(Of TodoTag)

internal class TodoTagger : ITagger<TodoTag>

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";

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;
}

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());
                }
            }
        }
    }
}

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;

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

Import the IClassifierAggregatorService.

<Import()>
Friend AggregatorService As IClassifierAggregatorService

[Import]
internal IClassifierAggregatorService AggregatorService;

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

Build the solution.
Run the project by pressing F5. A second instance of Visual Studio is instantiated.
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.)
Open a code file that has comments. Add the word "todo" to one of the comment sections.
A light blue circle that has a dark blue outline should appear in the indicator margin to the left of the code window.

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