Turn TextArea.OverstrikeMode into a dependency property.

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/Caret.cs

@@ -53,6 +53,13 @@ namespace ICSharpCode.AvalonEdit.Editing
 			textView.ScrollOffsetChanged += TextView_ScrollOffsetChanged;
 		}
 		
+		internal void UpdateIfVisible()
+		{
+			if (visible) {
+				Show();
+			}
+		}
+		
 		void TextView_VisualLinesChanged(object sender, EventArgs e)
 		{
 			if (visible) {
@@ -414,8 +421,7 @@ namespace ICSharpCode.AvalonEdit.Editing
 		{
 			if (textView != null && textView.Document != null) {
 				VisualLine visualLine = textView.GetOrConstructVisualLine(textView.Document.GetLineByNumber(position.Line));
-				return (this.textView.Options.AllowOverstrikeMode && this.textArea.OverstrikeMode)
-					? CalcCaretOverstrikeRectangle(visualLine) : CalcCaretRectangle(visualLine);
+				return textArea.OverstrikeMode ? CalcCaretOverstrikeRectangle(visualLine) : CalcCaretRectangle(visualLine);
 			} else {
 				return Rect.Empty;
 			}
@@ -470,12 +476,7 @@ namespace ICSharpCode.AvalonEdit.Editing
 			if (caretAdorner != null && textView != null) {
 				VisualLine visualLine = textView.GetVisualLine(position.Line);
 				if (visualLine != null) {
-					Rect caretRect;
-					if (this.textView.Options.AllowOverstrikeMode && this.textArea.OverstrikeMode) {
-						caretRect = CalcCaretOverstrikeRectangle(visualLine);
-					} else {
-						caretRect = CalcCaretRectangle(visualLine);
-					}
+					Rect caretRect = this.textArea.OverstrikeMode ? CalcCaretOverstrikeRectangle(visualLine) : CalcCaretRectangle(visualLine);
 					// Create Win32 caret so that Windows knows where our managed caret is. This is necessary for
 					// features like 'Follow text editing' in the Windows Magnifier.
 					if (!hasWin32Caret) {

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/CaretLayer.cs

@@ -94,12 +94,13 @@ namespace ICSharpCode.AvalonEdit.Editing
 				if (caretBrush == null)
 					caretBrush = (Brush)textView.GetValue(TextBlock.ForegroundProperty);
 				
-				if (this.textArea.Options.AllowOverstrikeMode && this.textArea.OverstrikeMode) {
+				if (this.textArea.OverstrikeMode) {
 					SolidColorBrush scBrush = caretBrush as SolidColorBrush;
 					if (scBrush != null) {
 						Color brushColor = scBrush.Color;
 						Color newColor = Color.FromArgb(100, brushColor.R, brushColor.G, brushColor.B);
 						caretBrush = new SolidColorBrush(newColor);
+						caretBrush.Freeze();
 					}
 				}
 				

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/TextArea.cs

@@ -25,6 +25,7 @@ using System.Linq;
 using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Controls.Primitives;
+using System.Windows.Documents;
 using System.Windows.Input;
 using System.Windows.Media;
 using System.Windows.Threading;
@@ -882,8 +883,8 @@ namespace ICSharpCode.AvalonEdit.Editing
 				if (e.Text == "\n" || e.Text == "\r" || e.Text == "\r\n")
 					ReplaceSelectionWithNewLine();
 				else {
-					if (overstrikeMode && Selection.IsEmpty && Document.GetLineByNumber(Caret.Line).EndOffset > Caret.Offset)
-						Selection = Selection.Create(this, Caret.Offset, Caret.Offset+e.Text.Length);
+					if (OverstrikeMode && Selection.IsEmpty && Document.GetLineByNumber(Caret.Line).EndOffset > Caret.Offset)
+						EditingCommands.SelectRightByCharacter.Execute(null, this);
 					ReplaceSelectionWithText(e.Text);
 				}
 				OnTextEntered(e);
@@ -971,11 +972,8 @@ namespace ICSharpCode.AvalonEdit.Editing
 		{
 			base.OnPreviewKeyDown(e);
 			
-			if (!this.Options.AllowOverstrikeMode) {
-				this.overstrikeMode = false;
-			} else if (!e.Handled && e.Key == Key.Insert) {
-				this.overstrikeMode = !this.overstrikeMode;
-				this.caret.Show();
+			if (!e.Handled && e.Key == Key.Insert && this.Options.AllowToggleOverstrikeMode) {
+				this.OverstrikeMode = !this.OverstrikeMode;
 				e.Handled = true;
 				return;
 			}
@@ -1047,11 +1045,19 @@ namespace ICSharpCode.AvalonEdit.Editing
 		
 		#region Overstrike mode
 		
-		bool overstrikeMode = false;
+		/// <summary>
+		/// The <see cref="OverstrikeMode"/> dependency property.
+		/// </summary>
+		public static readonly DependencyProperty OverstrikeModeProperty =
+			DependencyProperty.Register("OverstrikeMode", typeof(bool), typeof(TextArea),
+			                            new FrameworkPropertyMetadata(Boxes.False));
 		
-		public bool OverstrikeMode
-		{
-			get { return this.overstrikeMode; }
+		/// <summary>
+		/// Gets/Sets whether overstrike mode is active.
+		/// </summary>
+		public bool OverstrikeMode {
+			get { return (bool)GetValue(OverstrikeModeProperty); }
+			set { SetValue(OverstrikeModeProperty, value); }
 		}
 		
 		#endregion
@@ -1073,6 +1079,8 @@ namespace ICSharpCode.AvalonEdit.Editing
 			    || e.Property == SelectionCornerRadiusProperty)
 			{
 				textView.Redraw();
+			} else if (e.Property == OverstrikeModeProperty) {
+				caret.UpdateIfVisible();
 			}
 		}
 		

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/TextEditorOptions.cs

@@ -478,18 +478,18 @@ namespace ICSharpCode.AvalonEdit
 			}
 		}
 		
-		bool allowOverstrikeMode = false;
+		bool allowToggleOverstrikeMode = false;
 		
 		/// <summary>
-		/// Gets/Sets if the user is allowed to switch to overstrike mode.
+		/// Gets/Sets if the user is allowed to enable/disable overstrike mode.
 		/// </summary>
 		[DefaultValue(false)]
-		public bool AllowOverstrikeMode {
-			get { return allowOverstrikeMode; }
+		public bool AllowToggleOverstrikeMode {
+			get { return allowToggleOverstrikeMode; }
 			set {
-				if (allowOverstrikeMode != value) {
-					allowOverstrikeMode = value;
-					OnPropertyChanged("AllowOverstrikeMode");
+				if (allowToggleOverstrikeMode != value) {
+					allowToggleOverstrikeMode = value;
+					OnPropertyChanged("AllowToggleOverstrikeMode");
 				}
 			}
 		}