diff --git a/OpenCover.UI/OpenCover.UI.VS2013.csproj b/OpenCover.UI/OpenCover.UI.VS2013.csproj
index 54988b8..f3262c3 100644
--- a/OpenCover.UI/OpenCover.UI.VS2013.csproj
+++ b/OpenCover.UI/OpenCover.UI.VS2013.csproj
@@ -179,6 +179,7 @@
     <Compile Include="Glyphs\LineCoverageGlyphFactoryProvider.cs" />
     <Compile Include="Helpers\LineCoverageState.cs" />
     <Compile Include="Settings.cs" />
+    <Compile Include="Tagger\ClassificationTypes.cs" />
     <Compile Include="Tagger\LineCoverageTag.cs" />
     <Compile Include="Tagger\LineCoverageTagger.cs" />
     <Compile Include="Commands\CodeCoverageToolWindowCommand.cs" />
diff --git a/OpenCover.UI/OpenCover.UI.csproj b/OpenCover.UI/OpenCover.UI.csproj
index 0d04014..7b58371 100644
--- a/OpenCover.UI/OpenCover.UI.csproj
+++ b/OpenCover.UI/OpenCover.UI.csproj
@@ -179,6 +179,7 @@
     <Compile Include="Glyphs\LineCoverageGlyphFactoryProvider.cs" />
     <Compile Include="Helpers\LineCoverageState.cs" />
     <Compile Include="Settings.cs" />
+    <Compile Include="Tagger\ClassificationTypes.cs" />
     <Compile Include="Tagger\LineCoverageTag.cs" />
     <Compile Include="Tagger\LineCoverageTagger.cs" />
     <Compile Include="Commands\CodeCoverageToolWindowCommand.cs" />
diff --git a/OpenCover.UI/Settings.cs b/OpenCover.UI/Settings.cs
index 95e2c4b..d823a23 100644
--- a/OpenCover.UI/Settings.cs
+++ b/OpenCover.UI/Settings.cs
@@ -1,11 +1,6 @@
-using Microsoft.VisualStudio.Settings;
-using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Linq;
+using System.ComponentModel;
 using System.Runtime.CompilerServices;
-using System.Text;
-using System.Threading.Tasks;
+using Microsoft.VisualStudio.Settings;
 
 namespace OpenCover.UI
 {
@@ -29,8 +24,8 @@ public Settings(WritableSettingsStore configurationSettingsStore)
         {
             _store = configurationSettingsStore;
 
-            _showLinesColored = _store.GetBoolean(SETTINGS_PATH, "ShowLinesColored", false);
-            _showCoverageGlyphs = _store.GetBoolean(SETTINGS_PATH, "ShowCoverageGlyphs", true);
+            _showLinesColored = _store.GetBoolean(SETTINGS_PATH, SettingNames.ShowLinesColored, false);
+            _showCoverageGlyphs = _store.GetBoolean(SETTINGS_PATH, SettingNames.ShowCoverageGlyphs, true);
         }
 
         /// <summary>
@@ -89,5 +84,11 @@ private void WriteBoolean(bool value, [CallerMemberName] string propertyName = n
 
             _store.SetBoolean(SETTINGS_PATH, propertyName, value);
         }
+
+        public static class SettingNames
+        {
+            public const string ShowLinesColored = "ShowLinesColored";
+            public const string ShowCoverageGlyphs = "ShowCoverageGlyphs";
+        }
     }
 }
diff --git a/OpenCover.UI/Tagger/ClassificationTypes.cs b/OpenCover.UI/Tagger/ClassificationTypes.cs
new file mode 100644
index 0000000..543d2b4
--- /dev/null
+++ b/OpenCover.UI/Tagger/ClassificationTypes.cs
@@ -0,0 +1,8 @@
+namespace OpenCover.UI.Tagger
+{
+    public static class ClassificationTypes
+    {
+        public const string TextBackgroundCovered = "text-background-covered";
+        public const string TextBackgroundNotCovered = "text-background-notcovered";
+    }
+}
diff --git a/OpenCover.UI/Tagger/LineCoverageTag.cs b/OpenCover.UI/Tagger/LineCoverageTag.cs
index c51cef1..cca709a 100644
--- a/OpenCover.UI/Tagger/LineCoverageTag.cs
+++ b/OpenCover.UI/Tagger/LineCoverageTag.cs
@@ -1,9 +1,4 @@
 using Microsoft.VisualStudio.Text.Editor;
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 namespace OpenCover.UI.Tagger
 {    
diff --git a/OpenCover.UI/Tagger/LineCoverageTagger.cs b/OpenCover.UI/Tagger/LineCoverageTagger.cs
index f54eeb5..dedbe1a 100644
--- a/OpenCover.UI/Tagger/LineCoverageTagger.cs
+++ b/OpenCover.UI/Tagger/LineCoverageTagger.cs
@@ -1,11 +1,9 @@
 using System;
 using System.Collections.Generic;
-using System.ComponentModel.Composition;
+using System.ComponentModel;
 using Microsoft.VisualStudio.Text;
-using Microsoft.VisualStudio.Text.Tagging;
-using Microsoft.VisualStudio.Text.Editor;
 using Microsoft.VisualStudio.Text.Classification;
-using Microsoft.VisualStudio.Utilities;
+using Microsoft.VisualStudio.Text.Tagging;
 using OpenCover.UI.Views;
 
 namespace OpenCover.UI.Tagger
@@ -91,9 +89,9 @@ IEnumerable<ITagSpan<LineCoverageTag>> ITagger<LineCoverageTag>.GetTags(Normaliz
         /// </summary>
         /// <param name="sender"></param>
         /// <param name="e"></param>
-        void OnSettingsChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
+        void OnSettingsChanged(object sender, PropertyChangedEventArgs e)
         {
-            if (e.PropertyName == "ShowCoverageGlyphs")
+            if (e.PropertyName == Settings.SettingNames.ShowCoverageGlyphs)
                 RaiseAllTagsChanged();
         }
 
diff --git a/OpenCover.UI/Tagger/TextBackground.cs b/OpenCover.UI/Tagger/TextBackground.cs
index 716121d..a5fc62c 100644
--- a/OpenCover.UI/Tagger/TextBackground.cs
+++ b/OpenCover.UI/Tagger/TextBackground.cs
@@ -14,7 +14,7 @@ namespace OpenCover.UI.Tagger
 	public static class CoveredTextBackgroundTypeExports
 	{
 		[Export(typeof(ClassificationTypeDefinition))]
-		[Name("text-background-covered")]
+        [Name(ClassificationTypes.TextBackgroundCovered)]
 		public static ClassificationTypeDefinition OrdinaryClassificationType;
 	}
 
@@ -24,7 +24,7 @@ public static class CoveredTextBackgroundTypeExports
 	public static class NotCoveredTextBackgroundTypeExports
 	{
 		[Export(typeof(ClassificationTypeDefinition))]
-		[Name("text-background-notcovered")]
+        [Name(ClassificationTypes.TextBackgroundNotCovered)]
 		public static ClassificationTypeDefinition OrdinaryClassificationType;
 	}
 
@@ -32,8 +32,8 @@ public static class NotCoveredTextBackgroundTypeExports
 	/// Class defining background color for covered classes
 	/// </summary>
 	[Export(typeof(EditorFormatDefinition))]
-	[ClassificationType(ClassificationTypeNames = "text-background-covered")]
-	[Name("text-background-covered")]
+    [ClassificationType(ClassificationTypeNames = ClassificationTypes.TextBackgroundCovered)]
+    [Name(ClassificationTypes.TextBackgroundCovered)]
 	[UserVisible(true)]
 	[Order(After = Priority.High)]
 	public sealed class CoveredTextBackground : ClassificationFormatDefinition
@@ -52,8 +52,8 @@ public CoveredTextBackground()
 	/// Class defining background color for covered classes
 	/// </summary>
 	[Export(typeof(EditorFormatDefinition))]
-	[ClassificationType(ClassificationTypeNames = "text-background-notcovered")]
-	[Name("text-background-notcovered")]
+    [ClassificationType(ClassificationTypeNames = ClassificationTypes.TextBackgroundNotCovered)]
+    [Name(ClassificationTypes.TextBackgroundNotCovered)]
 	[UserVisible(true)]
 	[Order(After = Priority.High)]
 	public sealed class NotCoveredTextBackground : ClassificationFormatDefinition
diff --git a/OpenCover.UI/Tagger/TextTagger.cs b/OpenCover.UI/Tagger/TextTagger.cs
index 1aec564..2889911 100644
--- a/OpenCover.UI/Tagger/TextTagger.cs
+++ b/OpenCover.UI/Tagger/TextTagger.cs
@@ -1,19 +1,18 @@
 //
 // This source code is released under the GPL License; Please read license.md file for more details.
 //
-using Microsoft.VisualStudio.Shell;
+
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
 using Microsoft.VisualStudio.Text;
 using Microsoft.VisualStudio.Text.Classification;
 using Microsoft.VisualStudio.Text.Editor;
+using Microsoft.VisualStudio.Text.Formatting;
 using Microsoft.VisualStudio.Text.Operations;
 using Microsoft.VisualStudio.Text.Tagging;
 using OpenCover.UI.Glyphs;
 using OpenCover.UI.Helper;
-using OpenCover.UI.Helpers;
-using OpenCover.UI.Views;
-using System;
-using System.Collections.Generic;
-using System.Linq;
 
 namespace OpenCover.UI.Tagger
 {
@@ -95,7 +94,7 @@ public IEnumerable<ITagSpan<ClassificationTag>> GetTags(NormalizedSnapshotSpanCo
 
             foreach (var span in spansToSerach)
 			{
-				var covered = _spanCoverage.ContainsKey(span) ? _spanCoverage[span] : false;
+				var covered = _spanCoverage.ContainsKey(span) && _spanCoverage[span];
 				var tag = covered ? new ClassificationTag(_coveredType) : new ClassificationTag(_notCoveredType);
 				yield return new TagSpan<ClassificationTag>(span, tag);
 			}
@@ -119,22 +118,26 @@ public static TextTagger GetTagger(ITextView view)
         /// </summary>
         /// <param name="sender"></param>
         /// <param name="e"></param>
-        void OnSettingsChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
+        void OnSettingsChanged(object sender, PropertyChangedEventArgs e)
         {
-            if (e.PropertyName == "ShowLinesColored")
+            if (e.PropertyName == Settings.SettingNames.ShowLinesColored)
                 RaiseAllTagsChanged();
         }
 
         private void OnViewClosed(object sender, EventArgs e)
         {
-            _instances.Remove(sender as ITextView);
+            var key = sender as ITextView;
+            if (key != null)
+            {
+                _instances.Remove(key);
+            }
         }
 
-        /// <summary>
+	    /// <summary>
         /// Show spans for line only
         /// </summary>
         /// <param name="line"></param>
-        internal void ShowForLine(Microsoft.VisualStudio.Text.Formatting.IWpfTextViewLine line)
+        internal void ShowForLine(IWpfTextViewLine line)
         {
             _lineSpans = LineCoverageGlyphFactory.GetSpansForLine(line, _currentSpans);
             RaiseAllTagsChanged();
diff --git a/OpenCover.UI/Tagger/TextTaggerProvider.cs b/OpenCover.UI/Tagger/TextTaggerProvider.cs
index daa2810..66890ac 100644
--- a/OpenCover.UI/Tagger/TextTaggerProvider.cs
+++ b/OpenCover.UI/Tagger/TextTaggerProvider.cs
@@ -54,9 +54,9 @@ public ITagger<T> CreateTagger<T>(ITextView textView, ITextBuffer buffer) where
 
             // create new instance
             if (instance == null)
-            {                
-                var coveredClassType = Registry.GetClassificationType("text-background-covered");
-                var notCoveredClassType = Registry.GetClassificationType("text-background-notcovered");
+            {
+                var coveredClassType = Registry.GetClassificationType(ClassificationTypes.TextBackgroundCovered);
+                var notCoveredClassType = Registry.GetClassificationType(ClassificationTypes.TextBackgroundNotCovered);
                 instance = new TextTagger(textView, TextSearchService, coveredClassType, notCoveredClassType);
             }