The HighLigth word feature stopped working after the window was split and unsplit or after the preview margin was shown because these all share the same buffer.

We now add a counter to the SameWordHighlighterTagger and when the Counter reaches zero then the tagger stops tagging.
Also added a HighlightWord tagger to the example project that tags words inside text documents.

Author: RobertvanderHulst

demo/VSSDK.TestExtension/MEF/HighlightWord.cs

@@ -0,0 +1,29 @@
+using Microsoft.VisualStudio.Text.Operations;
+using Microsoft.VisualStudio.Text.Tagging;
+using Microsoft.VisualStudio.Utilities;
+using Community.VisualStudio.Toolkit;
+using System.ComponentModel.Composition;
+using Microsoft.VisualStudio.Text.Editor;
+
+namespace TestExtension.MEF
+{
+    /// <summary>
+    /// This class demonstrates a HighlightWord tagger for text files
+    /// and it only highlights whole words starting with a Letter
+    /// </summary>
+    [Export(typeof(IViewTaggerProvider))]
+    [ContentType("Text")]
+    [TagType(typeof(TextMarkerTag))]
+    [TextViewRole(PredefinedTextViewRoles.PrimaryDocument)]
+    internal class HighlightWordTaggerProvider : SameWordHighlighterBase
+    {
+        public override FindOptions FindOptions => FindOptions.WholeWord;
+        public override bool ShouldHighlight(string text)
+        {
+            if (text?.Length > 0)
+                return char.IsLetter(text[0]);
+            return false;
+        }
+
+    }
+}

demo/VSSDK.TestExtension/VSSDK.TestExtension.csproj

@@ -61,6 +61,7 @@
     <Compile Include="Commands\RunnerWindowCommand.cs" />
     <Compile Include="Commands\ThemeWindowCommand.cs" />
     <Compile Include="Commands\UnloadSelectedProject.cs" />
+    <Compile Include="MEF\HighlightWord.cs" />
     <Compile Include="MEF\TextViewCreationListener.cs" />
     <Compile Include="Options\General.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />

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

@@ -10,6 +10,7 @@
 
 namespace Community.VisualStudio.Toolkit
 {
+
     /// <summary>
     /// A base class for providing same-word highlighting.
     /// </summary>
@@ -48,8 +49,11 @@ public ITagger<T> CreateTagger<T>(ITextView textView, ITextBuffer buffer) where
         {
             ITextStructureNavigator? navigator = _textStructureNavigatorSelector?.GetTextStructureNavigator(textView.TextBuffer);
 
-            return (ITagger<T>)buffer.Properties.GetOrCreateSingletonProperty(() =>
+            var tagger = textView.Properties.GetOrCreateSingletonProperty(() =>
                 new SameWordHighlighterTagger(textView, buffer, _textSearchService, navigator, this));
+            tagger.Counter += 1;
+
+            return (ITagger<T>)tagger;
         }
     }
 
@@ -60,6 +64,7 @@ public HighlightWordTag(string tagName) : base(tagName) { }
 
     internal class SameWordHighlighterTagger : ITagger<HighlightWordTag>, IDisposable
     {
+        internal int Counter;
         private readonly ITextView _view;
         private readonly ITextBuffer _buffer;
         private readonly ITextSearchService? _textSearchService;
@@ -83,6 +88,7 @@ public SameWordHighlighterTagger(ITextView view, ITextBuffer sourceBuffer, IText
             _currentWord = null;
             _view.Caret.PositionChanged += CaretPositionChanged;
             _view.LayoutChanged += ViewLayoutChanged;
+            Counter = 0;
         }
 
         private void ViewLayoutChanged(object sender, TextViewLayoutChangedEventArgs e)
@@ -226,11 +232,14 @@ public void Dispose()
         {
             if (!_isDisposed)
             {
-                _view.Caret.PositionChanged -= CaretPositionChanged;
-                _view.LayoutChanged -= ViewLayoutChanged;
+                this.Counter -= 1;
+                if (this.Counter == 0)
+                {
+                    _view.Caret.PositionChanged -= CaretPositionChanged;
+                    _view.LayoutChanged -= ViewLayoutChanged;
+                    _isDisposed = true;
+                }
             }
-
-            _isDisposed = true;
         }
 
         public event EventHandler<SnapshotSpanEventArgs>? TagsChanged;