Walkthrough: Highlighting Text

Article
04/21/2015

You can add different visual effects to the editor by creating Managed Extensibility Framework (MEF) component parts. This walkthrough shows how to highlight every occurrence of the current word in a text file. If a word occurs more than one time in a text file, and you position the caret in one occurrence, every occurrence is highlighted.

Prerequisites

To follow this walkthrough, you must install the Visual Studio 2013 SDK. For more information, see Visual Studio Software Development Kit (SDK).

Creating a MEF Project

To create a MEF project

Create an Editor Classifier project. Name the solution HighlightWordTest.
Open the source.extension.vsixmanifest file in the VSIX Manifest Editor.
Make sure that the Assets tab contains a MEF Component content type and that Project is set to the name of the project.
Save and close source.extension.vsixmanifest.
Delete the existing class files.

Defining a TextMarkerTag

The first step in highlighting text is to subclass TextMarkerTag and define its appearance.

To define a TextMarkerTag and a MarkerFormatDefinition

Add a class file and name it HighlightWordTag.

Import the following namespaces.

Imports System
Imports System.Collections.Generic
Imports System.ComponentModel.Composition
Imports System.Linq
Imports System.Threading
Imports System.Windows.Media
Imports Microsoft.VisualStudio.Text
Imports Microsoft.VisualStudio.Text.Classification
Imports Microsoft.VisualStudio.Text.Editor
Imports Microsoft.VisualStudio.Text.Operations
Imports Microsoft.VisualStudio.Text.Tagging
Imports Microsoft.VisualStudio.Utilities

using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.Linq;
using System.Threading;
using System.Windows.Media;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Classification;
using Microsoft.VisualStudio.Text.Editor;
using Microsoft.VisualStudio.Text.Operations;
using Microsoft.VisualStudio.Text.Tagging;
using Microsoft.VisualStudio.Utilities;

Create a class that inherits from TextMarkerTag and name it HighlightWordTag.

Friend Class HighlightWordTag
    Inherits TextMarkerTag

internal class HighlightWordTag : TextMarkerTag

Create a second class that inherits from MarkerFormatDefinition, and name it HighlightWordFormatDefinition. In order to use this format definition for your tag, you must export it with the following attributes:

NameAttribute: tags use this to reference this format
UserVisibleAttribute: this causes the format to appear in the UI

<Export(GetType(EditorFormatDefinition))>
<Name("MarkerFormatDefinition/HighlightWordFormatDefinition")>
<UserVisible(True)>
Friend Class HighlightWordFormatDefinition
    Inherits MarkerFormatDefinition

[Export(typeof(EditorFormatDefinition))]
[Name("MarkerFormatDefinition/HighlightWordFormatDefinition")]
[UserVisible(true)]
internal class HighlightWordFormatDefinition : MarkerFormatDefinition

In the constructor for HighlightWordFormatDefinition, define its display name and appearance. The Background property defines the fill color, while the Foreground property defines the border color.

Public Sub New()
    Me.BackgroundColor = Colors.LightBlue
    Me.ForegroundColor = Colors.DarkBlue
    Me.DisplayName = "Highlight Word" 
    Me.ZOrder = 5
End Sub

public HighlightWordFormatDefinition()
{
    this.BackgroundColor = Colors.LightBlue;
    this.ForegroundColor = Colors.DarkBlue;
    this.DisplayName = "Highlight Word";
    this.ZOrder = 5;
}

In the constructor for HighlightWordTag, pass in the name of the format definition you just created.

Public Sub New()
    MyBase.New("MarkerFormatDefinition/HighlightWordFormatDefinition")
End Sub

public HighlightWordTag() : base("MarkerFormatDefinition/HighlightWordFormatDefinition") { }

Implementing an ITagger

The next step is to implement the ITagger<T> interface. This interface assigns, to a given text buffer, tags that provide text highlighting and other visual effects.

To implement a tagger

Create a class that implements ITagger<T> of type HighlightWordTag, and name it HighlightWordTagger.

Friend Class HighlightWordTagger
    Implements ITagger(Of HighlightWordTag)

internal class HighlightWordTagger : ITagger<HighlightWordTag>

Add the following private fields and properties to the class:

An ITextView, which corresponds to the current text view.
An ITextBuffer, which corresponds to the text buffer that underlies the text view.
An ITextSearchService, which is used to find text.
An ITextStructureNavigator, which has methods for navigating within text spans.
A NormalizedSnapshotSpanCollection, which contains the set of words to highlight.
A SnapshotSpan, which corresponds to the current word.
A SnapshotPoint, which corresponds to the current position of the caret.
A lock object.

Private _View As ITextView
Private Property View() As ITextView
    Get 
        Return _View
    End Get 
    Set(ByVal value As ITextView)
        _View = value
    End Set 
End Property 
Private _SourceBuffer As ITextBuffer
Private Property SourceBuffer() As ITextBuffer
    Get 
        Return _SourceBuffer
    End Get 
    Set(ByVal value As ITextBuffer)
        _SourceBuffer = value
    End Set 
End Property 
Private _TextSearchService As ITextSearchService
Private Property TextSearchService() As ITextSearchService
    Get 
        Return _TextSearchService
    End Get 
    Set(ByVal value As ITextSearchService)
        _TextSearchService = value
    End Set 
End Property 
Private _TextStructureNavigator As ITextStructureNavigator
Private Property TextStructureNavigator() As ITextStructureNavigator
    Get 
        Return _TextStructureNavigator
    End Get 
    Set(ByVal value As ITextStructureNavigator)
        _TextStructureNavigator = value
    End Set 
End Property 
Private _WordSpans As NormalizedSnapshotSpanCollection
Private Property WordSpans() As NormalizedSnapshotSpanCollection
    Get 
        Return _WordSpans
    End Get 
    Set(ByVal value As NormalizedSnapshotSpanCollection)
        _WordSpans = value
    End Set 
End Property 
Private _CurrentWord As System.Nullable(Of SnapshotSpan)
Private Property CurrentWord() As System.Nullable(Of SnapshotSpan)
    Get 
        Return _CurrentWord
    End Get 
    Set(ByVal value As System.Nullable(Of SnapshotSpan))
        _CurrentWord = value
    End Set 
End Property 
Private _RequestedPoint As SnapshotPoint
Private Property RequestedPoint() As SnapshotPoint
    Get 
        Return _RequestedPoint
    End Get 
    Set(ByVal value As SnapshotPoint)
        _RequestedPoint = value
    End Set 
End Property 
Private updateLock As New Object()

ITextView View { get; set; }
ITextBuffer SourceBuffer { get; set; }
ITextSearchService TextSearchService { get; set; }
ITextStructureNavigator TextStructureNavigator { get; set; }
NormalizedSnapshotSpanCollection WordSpans { get; set; }
SnapshotSpan? CurrentWord { get; set; }
SnapshotPoint RequestedPoint { get; set; }
object updateLock = new object();

Add a constructor that initializes the properties listed earlier and adds LayoutChanged and PositionChanged event handlers.

Public Sub New(ByVal view As ITextView, ByVal sourceBuffer As ITextBuffer, ByVal textSearchService As ITextSearchService, ByVal textStructureNavigator As ITextStructureNavigator)
    Me.View = view
    Me.SourceBuffer = sourceBuffer
    Me.TextSearchService = textSearchService
    Me.TextStructureNavigator = textStructureNavigator
    Me.WordSpans = New NormalizedSnapshotSpanCollection()
    Me.CurrentWord = Nothing 
    AddHandler Me.View.Caret.PositionChanged, AddressOf CaretPositionChanged
    AddHandler Me.View.LayoutChanged, AddressOf ViewLayoutChanged
End Sub

public HighlightWordTagger(ITextView view, ITextBuffer sourceBuffer, ITextSearchService textSearchService,
ITextStructureNavigator textStructureNavigator)
{
    this.View = view;
    this.SourceBuffer = sourceBuffer;
    this.TextSearchService = textSearchService;
    this.TextStructureNavigator = textStructureNavigator;
    this.WordSpans = new NormalizedSnapshotSpanCollection();
    this.CurrentWord = null;
    this.View.Caret.PositionChanged += CaretPositionChanged;
    this.View.LayoutChanged += ViewLayoutChanged;
}

The event handlers both call the UpdateAtCaretPosition method.

Private Sub ViewLayoutChanged(ByVal sender As Object, ByVal e As TextViewLayoutChangedEventArgs)
    ' If a new snapshot wasn't generated, then skip this layout 
    If e.NewSnapshot IsNot e.OldSnapshot Then
        UpdateAtCaretPosition(View.Caret.Position)
    End If 
End Sub 

Private Sub CaretPositionChanged(ByVal sender As Object, ByVal e As CaretPositionChangedEventArgs)
    UpdateAtCaretPosition(e.NewPosition)
End Sub

void ViewLayoutChanged(object sender, TextViewLayoutChangedEventArgs e)
{
    // If a new snapshot wasn't generated, then skip this layout 
    if (e.NewSnapshot != e.OldSnapshot)
    {
        UpdateAtCaretPosition(View.Caret.Position);
    }
}

void CaretPositionChanged(object sender, CaretPositionChangedEventArgs e)
{
    UpdateAtCaretPosition(e.NewPosition);
}

You must also add a TagsChanged event that will be called by the update method.

Public Event TagsChanged(ByVal sender As Object, ByVal e As SnapshotSpanEventArgs) _
    Implements ITagger(Of HighlightWordTag).TagsChanged

public event EventHandler<SnapshotSpanEventArgs> TagsChanged;

The UpdateAtCaretPosition() method finds every word in the text buffer that is identical to the word where the cursor is positioned and constructs a list of SnapshotSpan objects that correspond to the occurrences of the word. It then calls SynchronousUpdate, which raises the TagsChanged event.

Private Sub UpdateAtCaretPosition(ByVal caretPosition As CaretPosition)
    Dim point As System.Nullable(Of SnapshotPoint) = caretPosition.Point.GetPoint(SourceBuffer, caretPosition.Affinity)

    If Not point.HasValue Then 
        Exit Sub 
    End If 

    ' If the new caret position is still within the current word (and on the same snapshot), we don't need to check it 
    If CurrentWord.HasValue AndAlso CurrentWord.Value.Snapshot Is View.TextSnapshot AndAlso point.Value > CurrentWord.Value.Start AndAlso point.Value < CurrentWord.Value.[End] Then 
        Exit Sub 
    End If

    RequestedPoint = point.Value
    UpdateWordAdornments()
End Sub 

Private Sub UpdateWordAdornments()
    Dim currentRequest As SnapshotPoint = RequestedPoint
    Dim wordSpans As New List(Of SnapshotSpan)()
    'Find all words in the buffer like the one the caret is on 
    Dim word As TextExtent = TextStructureNavigator.GetExtentOfWord(currentRequest)
    Dim foundWord As Boolean = True 
    'If we've selected something not worth highlighting, we might have missed a "word" by a little bit 
    If Not WordExtentIsValid(currentRequest, word) Then 
        'Before we retry, make sure it is worthwhile 
        If word.Span.Start <> currentRequest OrElse currentRequest = currentRequest.GetContainingLine().Start OrElse Char.IsWhiteSpace((currentRequest - 1).GetChar()) Then
            foundWord = False 
        Else 
            ' Try again, one character previous.  
            'If the caret is at the end of a word, pick up the word.
            word = TextStructureNavigator.GetExtentOfWord(currentRequest - 1)

            'If the word still isn't valid, we're done 
            If Not WordExtentIsValid(currentRequest, word) Then
                foundWord = False 
            End If 
        End If 
    End If 

    If Not foundWord Then 
        'If we couldn't find a word, clear out the existing markers
        SynchronousUpdate(currentRequest, New NormalizedSnapshotSpanCollection(), Nothing)
        Exit Sub 
    End If 

    Dim currentWord__1 As SnapshotSpan = word.Span
    'If this is the current word, and the caret moved within a word, we're done. 
    If CurrentWord.HasValue AndAlso currentWord__1 = CurrentWord Then 
        Exit Sub 
    End If 

    'Find the new spans 
    Dim findData As New FindData(currentWord__1.GetText(), currentWord__1.Snapshot)
    findData.FindOptions = FindOptions.WholeWord Or FindOptions.MatchCase

    wordSpans.AddRange(TextSearchService.FindAll(findData))

    'If another change hasn't happened, do a real update 
    If currentRequest = RequestedPoint Then
        SynchronousUpdate(currentRequest, New NormalizedSnapshotSpanCollection(wordSpans), currentWord__1)
    End If 
End Sub 
Private Shared Function WordExtentIsValid(ByVal currentRequest As SnapshotPoint, ByVal word As TextExtent) As Boolean 
    Return word.IsSignificant AndAlso currentRequest.Snapshot.GetText(word.Span).Any(Function(c) Char.IsLetter(c))
End Function

void UpdateAtCaretPosition(CaretPosition caretPosition)
{
    SnapshotPoint? point = caretPosition.Point.GetPoint(SourceBuffer, caretPosition.Affinity);

    if (!point.HasValue)
        return;

    // If the new caret position is still within the current word (and on the same snapshot), we don't need to check it 
    if (CurrentWord.HasValue
        && CurrentWord.Value.Snapshot == View.TextSnapshot
        && point.Value >= CurrentWord.Value.Start
        && point.Value <= CurrentWord.Value.End)
    {
        return;
    }

    RequestedPoint = point.Value;
    UpdateWordAdornments();
}

void UpdateWordAdornments()
{
    SnapshotPoint currentRequest = RequestedPoint;
    List<SnapshotSpan> wordSpans = new List<SnapshotSpan>();
    //Find all words in the buffer like the one the caret is on
    TextExtent word = TextStructureNavigator.GetExtentOfWord(currentRequest);
    bool foundWord = true;
    //If we've selected something not worth highlighting, we might have missed a "word" by a little bit
    if (!WordExtentIsValid(currentRequest, word))
    {
        //Before we retry, make sure it is worthwhile 
        if (word.Span.Start != currentRequest
             || currentRequest == currentRequest.GetContainingLine().Start
             || char.IsWhiteSpace((currentRequest - 1).GetChar()))
        {
            foundWord = false;
        }
        else
        {
            // Try again, one character previous.  
            //If the caret is at the end of a word, pick up the word.
            word = TextStructureNavigator.GetExtentOfWord(currentRequest - 1);

            //If the word still isn't valid, we're done 
            if (!WordExtentIsValid(currentRequest, word))
                foundWord = false;
        }
    }

    if (!foundWord)
    {
        //If we couldn't find a word, clear out the existing markers
        SynchronousUpdate(currentRequest, new NormalizedSnapshotSpanCollection(), null);
        return;
    }

    SnapshotSpan currentWord = word.Span;
    //If this is the current word, and the caret moved within a word, we're done. 
    if (CurrentWord.HasValue && currentWord == CurrentWord)
        return;

    //Find the new spans
    FindData findData = new FindData(currentWord.GetText(), currentWord.Snapshot);
    findData.FindOptions = FindOptions.WholeWord | FindOptions.MatchCase;

    wordSpans.AddRange(TextSearchService.FindAll(findData));

    //If another change hasn't happened, do a real update 
    if (currentRequest == RequestedPoint)
        SynchronousUpdate(currentRequest, new NormalizedSnapshotSpanCollection(wordSpans), currentWord);
}
static bool WordExtentIsValid(SnapshotPoint currentRequest, TextExtent word)
{
    return word.IsSignificant
        && currentRequest.Snapshot.GetText(word.Span).Any(c => char.IsLetter(c));
}

The SynchronousUpdate performs a synchronous update on the WordSpans and CurrentWord properties, and raises the TagsChanged event.

Private Sub SynchronousUpdate(ByVal currentRequest As SnapshotPoint, ByVal newSpans As NormalizedSnapshotSpanCollection, ByVal newCurrentWord As System.Nullable(Of SnapshotSpan))
    SyncLock updateLock
        If currentRequest <> RequestedPoint Then 
            Exit Sub 
        End If

        WordSpans = newSpans
        CurrentWord = newCurrentWord

        RaiseEvent TagsChanged(Me, New SnapshotSpanEventArgs(New SnapshotSpan(SourceBuffer.CurrentSnapshot, 0, SourceBuffer.CurrentSnapshot.Length)))
    End SyncLock 
End Sub

void SynchronousUpdate(SnapshotPoint currentRequest, NormalizedSnapshotSpanCollection newSpans, SnapshotSpan? newCurrentWord)
{
    lock (updateLock)
    {
        if (currentRequest != RequestedPoint)
            return;

        WordSpans = newSpans;
        CurrentWord = newCurrentWord;

        var tempEvent = TagsChanged;
        if (tempEvent != null)
            tempEvent(this, new SnapshotSpanEventArgs(new SnapshotSpan(SourceBuffer.CurrentSnapshot, 0, SourceBuffer.CurrentSnapshot.Length)));
    }
}

You must implement the GetTags method. This method takes a collection of SnapshotSpan objects and returns an enumeration of tag spans.

In C#, implement this method as a yield iterator, which enables lazy evaluation (that is, evaluation of the set only when individual items are accessed) of the tags. In Visual Basic, add the tags to a list and return the list.

Here the method returns a TagSpan<T> object that has a "blue" TextMarkerTag, which provides a blue background.

Public Function GetTags(ByVal spans As NormalizedSnapshotSpanCollection) As IEnumerable(Of ITagSpan(Of HighlightWordTag)) Implements ITagger(Of HighlightWordTag).GetTags
    If CurrentWord Is Nothing Then 
        Return Nothing 
        Exit Function 
    End If 

    ' Hold on to a "snapshot" of the word spans and current word, so that we maintain the same 
    ' collection throughout 
    Dim currentWord__1 As SnapshotSpan = CurrentWord.Value
    Dim wordSpans__2 As NormalizedSnapshotSpanCollection = WordSpans

    If spans.Count = 0 OrElse WordSpans.Count = 0 Then 
        Return Nothing 
        Exit Function 
    End If 

    ' If the requested snapshot isn't the same as the one our words are on, translate our spans to the expected snapshot 
    If spans(0).Snapshot IsNot wordSpans__2(0).Snapshot Then
        wordSpans__2 = New NormalizedSnapshotSpanCollection(wordSpans__2.[Select](Function(span) span.TranslateTo(spans(0).Snapshot, SpanTrackingMode.EdgeExclusive)))

        currentWord__1 = currentWord__1.TranslateTo(spans(0).Snapshot, SpanTrackingMode.EdgeExclusive)
    End If 
    'in order to emulate the C# yield return functionality, 
    'create a list and add all the relevant spans to it, then return the list 
    Dim list As List(Of TagSpan(Of HighlightWordTag))
    list = New List(Of TagSpan(Of HighlightWordTag))()

    If spans.OverlapsWith(New NormalizedSnapshotSpanCollection(currentWord__1)) Then
        list.Add(New TagSpan(Of HighlightWordTag)(CurrentWord, New HighlightWordTag()))
    End If 

    For Each span As SnapshotSpan In NormalizedSnapshotSpanCollection.Overlap(spans, wordSpans__2)
        list.Add(New TagSpan(Of HighlightWordTag)(span, New HighlightWordTag()))
    Next 
    Return List
End Function

public IEnumerable<ITagSpan<HighlightWordTag>> GetTags(NormalizedSnapshotSpanCollection spans)
{
    if (CurrentWord == null)
        yield break;

    // Hold on to a "snapshot" of the word spans and current word, so that we maintain the same
    // collection throughout
    SnapshotSpan currentWord = CurrentWord.Value;
    NormalizedSnapshotSpanCollection wordSpans = WordSpans;

    if (spans.Count == 0 || wordSpans.Count == 0)
        yield break;

    // If the requested snapshot isn't the same as the one our words are on, translate our spans to the expected snapshot 
    if (spans[0].Snapshot != wordSpans[0].Snapshot)
    {
        wordSpans = new NormalizedSnapshotSpanCollection(
            wordSpans.Select(span => span.TranslateTo(spans[0].Snapshot, SpanTrackingMode.EdgeExclusive)));

        currentWord = currentWord.TranslateTo(spans[0].Snapshot, SpanTrackingMode.EdgeExclusive);
    }

    // First, yield back the word the cursor is under (if it overlaps) 
    // Note that we'll yield back the same word again in the wordspans collection; 
    // the duplication here is expected. 
    if (spans.OverlapsWith(new NormalizedSnapshotSpanCollection(currentWord)))
        yield return new TagSpan<HighlightWordTag>(currentWord, new HighlightWordTag());

    // Second, yield all the other words in the file 
    foreach (SnapshotSpan span in NormalizedSnapshotSpanCollection.Overlap(spans, wordSpans))
    {
        yield return new TagSpan<HighlightWordTag>(span, new HighlightWordTag());
    }
}

Creating a Tagger Provider

To create your tagger, you must implement a IViewTaggerProvider. This class is a MEF component part, so you must set the correct attributes so that this extension is recognized.

Note

For more information about MEF, see Managed Extensibility Framework (MEF).

To create a tagger provider

Create a class named HighlightWordTaggerProvider that implements IViewTaggerProvider, and export it with a ContentTypeAttribute of "text" and a TagTypeAttribute of TextMarkerTag.

<Export(GetType(IViewTaggerProvider))>
<ContentType("text")>
<TagType(GetType(TextMarkerTag))>
Friend Class HighlightWordTaggerProvider
    Implements IViewTaggerProvider

[Export(typeof(IViewTaggerProvider))]
[ContentType("text")]
[TagType(typeof(TextMarkerTag))]
internal class HighlightWordTaggerProvider : IViewTaggerProvider

You must import two editor services, the ITextSearchService and the ITextStructureNavigatorSelectorService, to instantiate the tagger.

Private _TextSearchService As ITextSearchService
<Import()> _
Friend Property TextSearchService() As ITextSearchService
    Get 
        Return _TextSearchService
    End Get 
    Set(ByVal value As ITextSearchService)
        _TextSearchService = value
    End Set 
End Property 

Private _TextStructureNavigatorSelector As ITextStructureNavigatorSelectorService
<Import()>
Friend Property TextStructureNavigatorSelector() As ITextStructureNavigatorSelectorService
    Get 
        Return _TextStructureNavigatorSelector
    End Get 
    Set(ByVal value As ITextStructureNavigatorSelectorService)
        _TextStructureNavigatorSelector = value
    End Set 
End Property

[Import]
internal ITextSearchService TextSearchService { get; set; }

[Import]
internal ITextStructureNavigatorSelectorService TextStructureNavigatorSelector { get; set; }

Implement the CreateTagger<T> method to return an instance of HighlightWordTagger.

Public Function CreateTagger(Of T As ITag)(ByVal textView As ITextView, ByVal buffer As ITextBuffer) As ITagger(Of T) Implements IViewTaggerProvider.CreateTagger
    'provide highlighting only on the top buffer 
    If textView.TextBuffer IsNot buffer Then 
        Return Nothing 
    End If 

    Dim textStructureNavigator As ITextStructureNavigator = TextStructureNavigatorSelector.GetTextStructureNavigator(buffer)

    Return TryCast(New HighlightWordTagger(textView, buffer, TextSearchService, textStructureNavigator), ITagger(Of T))
End Function

public ITagger<T> CreateTagger<T>(ITextView textView, ITextBuffer buffer) where T : ITag
{
    //provide highlighting only on the top buffer 
    if (textView.TextBuffer != buffer)
        return null;

    ITextStructureNavigator textStructureNavigator =
        TextStructureNavigatorSelector.GetTextStructureNavigator(buffer);

    return new HighlightWordTagger(textView, buffer, TextSearchService, textStructureNavigator) as ITagger<T>;
}

Building and Testing the Code

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

To build and test the HighlightWordTest solution

Build the solution.
When you run this project in the debugger, a second instance of Visual Studio is instantiated.
Create a text file and type some text in which the words are repeated, for example, "hello hello hello".
Position the cursor in one of the occurrences of "hello". Every occurrence should be highlighted in blue.

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