Fix caret handles not updating to the latest caret points (#18794)

* fix caret handles not updating to the latest caret points

* Update TextSelectionCanvas.cs

src/Avalonia.Controls/Presenters/TextPresenter.cs

@@ -455,14 +455,14 @@ namespace Avalonia.Controls.Presenters
 
         internal (Point, Point) GetCaretPoints()
         {
-            var x = Math.Floor(_caretBounds.X) + 0.5;
-            var y = Math.Floor(_caretBounds.Y) + 0.5;
-            var b = Math.Ceiling(_caretBounds.Bottom) - 0.5;
-
             var caretIndex = _lastCharacterHit.FirstCharacterIndex + _lastCharacterHit.TrailingLength;
             var lineIndex = TextLayout.GetLineIndexFromCharacterIndex(caretIndex, _lastCharacterHit.TrailingLength > 0);
             var textLine = TextLayout.TextLines[lineIndex];
 
+            var x = Math.Floor(_caretBounds.X) + 0.5;
+            var y = Math.Floor(_caretBounds.Y) + 0.5;
+            var b = Math.Ceiling(_caretBounds.Bottom) - 0.5;
+
             if (_caretBounds.X > 0 && _caretBounds.X >= textLine.WidthIncludingTrailingWhitespace)
             {
                 x -= 1;

src/Avalonia.Controls/Primitives/TextSelectionCanvas.cs

@@ -262,6 +262,21 @@ namespace Avalonia.Controls.Primitives
         {
             if (_presenter == textPresenter)
                 return;
+
+            if (_textBox != null)
+            {
+                _textBox.RemoveHandler(TextBox.TextChangingEvent, TextChanged);
+                _textBox.RemoveHandler(KeyDownEvent, TextBoxKeyDown);
+                _textBox.RemoveHandler(PointerReleasedEvent, TextBoxPointerReleased);
+                _textBox.RemoveHandler(Gestures.HoldingEvent, TextBoxHolding);
+
+                _textBox.PropertyChanged -= TextBoxPropertyChanged;
+                _textBox.EffectiveViewportChanged -= TextBoxEffectiveViewportChanged;
+                _textBox.SizeChanged -= TextBox_SizeChanged;
+
+                _textBox = null;
+            }
+
             _presenter = textPresenter;
             if (_presenter != null)
             {
@@ -279,22 +294,6 @@ namespace Avalonia.Controls.Primitives
                     _textBox.SizeChanged += TextBox_SizeChanged;
                 }
             }
-            else
-            {
-                if (_textBox != null)
-                {
-                    _textBox.RemoveHandler(TextBox.TextChangingEvent, TextChanged);
-                    _textBox.RemoveHandler(KeyDownEvent, TextBoxKeyDown);
-                    _textBox.RemoveHandler(PointerReleasedEvent, TextBoxPointerReleased);
-                    _textBox.RemoveHandler(Gestures.HoldingEvent, TextBoxHolding);
-
-                    _textBox.PropertyChanged -= TextBoxPropertyChanged;
-                    _textBox.EffectiveViewportChanged -= TextBoxEffectiveViewportChanged;
-                    _textBox.SizeChanged -= TextBox_SizeChanged;
-                }
-
-                _textBox = null;
-            }
         }
 
         private void TextBox_SizeChanged(object? sender, SizeChangedEventArgs e)