Make sure only a single SameWordHighlighter is attached to a textbuffer.

Each TextView will register its events itself with the tagger from the textbuffer and when the textview is closed then the events are unregistered again.
The previous implementation was allocating way too many samewordhighlighters.
Also changed the color for the same word highlighters in the example code.

demo/VSSDK.TestExtension/MEF/HighlightWord.cs

@@ -4,9 +4,25 @@
 using Community.VisualStudio.Toolkit;
 using System.ComponentModel.Composition;
 using Microsoft.VisualStudio.Text.Editor;
-
+using Microsoft.VisualStudio.Text.Classification;
+using System.Windows.Media;
 namespace TestExtension.MEF
 {
+
+    [Export(typeof(EditorFormatDefinition))]
+    [Name("MarkerFormatDefinition/HighlightWordFormatDefinition")]
+    [UserVisible(true)]
+    internal class HighlightWordFormatDefinition : MarkerFormatDefinition
+    {
+        public HighlightWordFormatDefinition()
+        {
+            this.BackgroundColor = Colors.LightBlue;
+            this.ForegroundColor = Colors.DarkBlue;
+            this.DisplayName = "Highlight Word";
+            this.ZOrder = 5;
+        }
+    }
+
     /// <summary>
     /// This class demonstrates a HighlightWord tagger for text files
     /// and it only highlights whole words starting with a Letter

src/toolkit/Community.VisualStudio.Toolkit.Shared/MEF/SameWordHighlighterBase.cs

@@ -49,9 +49,9 @@ public ITagger<T> CreateTagger<T>(ITextView textView, ITextBuffer buffer) where
         {
             ITextStructureNavigator? navigator = _textStructureNavigatorSelector?.GetTextStructureNavigator(textView.TextBuffer);
 
-            var tagger = textView.Properties.GetOrCreateSingletonProperty(() =>
+            var tagger = buffer.Properties.GetOrCreateSingletonProperty(() =>
                 new SameWordHighlighterTagger(textView, buffer, _textSearchService, navigator, this));
-            tagger.Counter += 1;
+            tagger.RegisterEvents(textView);
 
             return (ITagger<T>)tagger;
         }
@@ -62,10 +62,9 @@ internal class HighlightWordTag : TextMarkerTag
         public HighlightWordTag(string tagName) : base(tagName) { }
     }
 
-    internal class SameWordHighlighterTagger : ITagger<HighlightWordTag>, IDisposable
+    internal class SameWordHighlighterTagger : ITagger<HighlightWordTag>
     {
         internal int Counter;
-        private readonly ITextView _view;
         private readonly ITextBuffer _buffer;
         private readonly ITextSearchService? _textSearchService;
         private readonly ITextStructureNavigator? _textStructureNavigator;
@@ -74,30 +73,52 @@ internal class SameWordHighlighterTagger : ITagger<HighlightWordTag>, IDisposabl
         private SnapshotSpan? _currentWord;
         private SnapshotPoint _requestedPoint;
         private bool _isDisposed;
+        private string _fileName="";
         private readonly object _syncLock = new();
 
         public SameWordHighlighterTagger(ITextView view, ITextBuffer sourceBuffer, ITextSearchService? textSearchService,
             ITextStructureNavigator? textStructureNavigator, SameWordHighlighterBase tagger)
         {
-            _view = view;
+            _fileName = sourceBuffer.GetFileName();
+            System.Diagnostics.Debug.WriteLine("Create new tagger for "+_fileName);
             _buffer = sourceBuffer;
             _textSearchService = textSearchService;
             _textStructureNavigator = textStructureNavigator;
             _tagger = tagger;
             _wordSpans = new NormalizedSnapshotSpanCollection();
             _currentWord = null;
-            _view.Caret.PositionChanged += CaretPositionChanged;
-            _view.LayoutChanged += ViewLayoutChanged;
             Counter = 0;
         }
 
+        internal void RegisterEvents(ITextView textView)
+        {
+
+            textView.Caret.PositionChanged += CaretPositionChanged;
+            textView.LayoutChanged += ViewLayoutChanged;
+            textView.Closed += TextView_Closed;
+            Counter += 1;
+            System.Diagnostics.Debug.WriteLine($"RegisterEvents {_fileName}: #{Counter} ");
+        }
+        internal void UnRegisterEvents(ITextView textView)
+        {
+            textView.Caret.PositionChanged -= CaretPositionChanged;
+            textView.LayoutChanged -= ViewLayoutChanged;
+            textView.Closed -= TextView_Closed;
+            Counter -= 1;
+            System.Diagnostics.Debug.WriteLine($"UnRegisterEvents {_fileName}: #{Counter} ");
+        }
         private void ViewLayoutChanged(object sender, TextViewLayoutChangedEventArgs e)
         {
             if (e.NewSnapshot != e.OldSnapshot)
             {
-                UpdateAtCaretPosition(_view.Caret.Position);
+                var view = (ITextView)sender;
+                UpdateAtCaretPosition(view.Caret.Position);
             }
         }
+        private void TextView_Closed(object sender, EventArgs e)
+        {
+            UnRegisterEvents((ITextView)sender);
+        }
 
         private void CaretPositionChanged(object sender, CaretPositionChangedEventArgs e)
         {
@@ -228,20 +249,6 @@ public IEnumerable<ITagSpan<HighlightWordTag>> GetTags(NormalizedSnapshotSpanCol
             }
         }
 
-        public void Dispose()
-        {
-            if (!_isDisposed)
-            {
-                this.Counter -= 1;
-                if (this.Counter == 0)
-                {
-                    _view.Caret.PositionChanged -= CaretPositionChanged;
-                    _view.LayoutChanged -= ViewLayoutChanged;
-                    _isDisposed = true;
-                }
-            }
-        }
-
         public event EventHandler<SnapshotSpanEventArgs>? TagsChanged;
     }
 }