Send a single Text change nofication when TextBlock.SelectedText is changed. (#5508)

* Added failing tests for #838.

* Fix Text events when setting SelectedText.

Only raise a single property changed event on `Text` when setting `SelectedText`. It's a bit ugly but the whole of `TextBox` needs a refactor...

Fixes #838.

src/Avalonia.Controls/TextBox.cs

@@ -642,15 +642,31 @@ namespace Avalonia.Controls
 
             if (!string.IsNullOrEmpty(input))
             {
-                DeleteSelection();
-                caretIndex = CaretIndex;
-                text = Text ?? string.Empty;
-                SetTextInternal(text.Substring(0, caretIndex) + input + text.Substring(caretIndex));
-                CaretIndex += input.Length;
-                ClearSelection();
-                if (IsUndoEnabled)
+                var oldText = _text;
+
+                _ignoreTextChanges = true;
+
+                try
                 {
-                    _undoRedoHelper.DiscardRedo();
+                    DeleteSelection(false);
+                    caretIndex = CaretIndex;
+                    text = Text ?? string.Empty;
+                    SetTextInternal(text.Substring(0, caretIndex) + input + text.Substring(caretIndex));
+                    CaretIndex += input.Length;
+                    ClearSelection();
+                    if (IsUndoEnabled)
+                    {
+                        _undoRedoHelper.DiscardRedo();
+                    }
+
+                    if (_text != oldText)
+                    {
+                        RaisePropertyChanged(TextProperty, oldText, _text);
+                    }
+                }
+                finally
+                {
+                    _ignoreTextChanges = false;
                 }
             }
         }
@@ -1285,7 +1301,7 @@ namespace Avalonia.Controls
             CaretIndex = SelectionEnd;
         }
 
-        private bool DeleteSelection()
+        private bool DeleteSelection(bool raiseTextChanged = true)
         {
             if (!IsReadOnly)
             {
@@ -1297,7 +1313,7 @@ namespace Avalonia.Controls
                     var start = Math.Min(selectionStart, selectionEnd);
                     var end = Math.Max(selectionStart, selectionEnd);
                     var text = Text;
-                    SetTextInternal(text.Substring(0, start) + text.Substring(end));
+                    SetTextInternal(text.Substring(0, start) + text.Substring(end), raiseTextChanged);
                     CaretIndex = start;
                     ClearSelection();
                     return true;
@@ -1348,16 +1364,23 @@ namespace Avalonia.Controls
             return i;
         }
 
-        private void SetTextInternal(string value)
+        private void SetTextInternal(string value, bool raiseTextChanged = true)
         {
-            try
+            if (raiseTextChanged)
             {
-                _ignoreTextChanges = true;
-                SetAndRaise(TextProperty, ref _text, value);
+                try
+                {
+                    _ignoreTextChanges = true;
+                    SetAndRaise(TextProperty, ref _text, value);
+                }
+                finally
+                {
+                    _ignoreTextChanges = false;
+                }
             }
-            finally
+            else
             {
-                _ignoreTextChanges = false;
+                _text = value;
             }
         }
 

tests/Avalonia.Controls.UnitTests/TextBoxTests.cs

@@ -784,6 +784,54 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Setting_SelectedText_Should_Fire_Single_Text_Changed_Notification()
+        {
+            using (UnitTestApplication.Start(Services))
+            {
+                var target = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    Text = "0123",
+                    AcceptsReturn = true,
+                    AcceptsTab = true,
+                    SelectionStart = 1,
+                    SelectionEnd = 3,
+                };
+
+                var values = new List<string>();
+                target.GetObservable(TextBox.TextProperty).Subscribe(x => values.Add(x));
+
+                target.SelectedText = "A";
+
+                Assert.Equal(new[] { "0123", "0A3" }, values);
+            }
+        }
+
+        [Fact]
+        public void Entering_Text_With_SelectedText_Should_Fire_Single_Text_Changed_Notification()
+        {
+            using (UnitTestApplication.Start(Services))
+            {
+                var target = new TextBox
+                {
+                    Template = CreateTemplate(),
+                    Text = "0123",
+                    AcceptsReturn = true,
+                    AcceptsTab = true,
+                    SelectionStart = 1,
+                    SelectionEnd = 3,
+                };
+
+                var values = new List<string>();
+                target.GetObservable(TextBox.TextProperty).Subscribe(x => values.Add(x));
+
+                RaiseTextEvent(target, "A");
+
+                Assert.Equal(new[] { "0123", "0A3" }, values);
+            }
+        }
+
         private static TestServices FocusServices => TestServices.MockThreadingInterface.With(
             focusManager: new FocusManager(),
             keyboardDevice: () => new KeyboardDevice(),