BREAKING CHANGE: Fixes #5366. Make View.Text notifications CWP-compliant and non-virtual

Examples/ReactiveExample/LoginView.cs

@@ -48,9 +48,9 @@ public LoginView (LoginViewModel viewModel)
                     .BindTo (unInput, x => x.Text)
                     .DisposeWith (_disposable);
 
-                unInput
-                    .Events ()
-                    .TextChanged
+                Observable.FromEventPattern (
+                        h => unInput.TextChanged += h,
+                        h => unInput.TextChanged -= h)
                     .Select (_ => unInput.Text)
                     .DistinctUntilChanged ()
                     .BindTo (ViewModel, x => x.Username)
@@ -79,9 +79,9 @@ public LoginView (LoginViewModel viewModel)
                     .BindTo (pwInput, x => x.Text)
                     .DisposeWith (_disposable);
 
-                pwInput
-                    .Events ()
-                    .TextChanged
+                Observable.FromEventPattern (
+                        h => pwInput.TextChanged += h,
+                        h => pwInput.TextChanged -= h)
                     .Select (_ => pwInput.Text)
                     .DistinctUntilChanged ()
                     .BindTo (ViewModel, x => x.Password)

Terminal.Gui/ViewBase/Adornment/ArrangerButton.cs

@@ -108,6 +108,7 @@ public ArrangeButtons ButtonType
             }
 
             _buttonType = value;
+            SetTextDirect (GetButtonGlyph ());
             ApplyOrientationAndDirection ();
             SetupKeyBindings ();
         }
@@ -123,19 +124,15 @@ public ArrangeButtons ButtonType
     public NavigationDirection Direction { get; set; }
 
     /// <inheritdoc/>
-    public override string Text
-    {
-        get =>
-            ButtonType switch
-            {
-                ArrangeButtons.Move => $"{Glyphs.Move}",
-                ArrangeButtons.AllSize => $"{Glyphs.SizeBottomRight}",
-                ArrangeButtons.LeftSize or ArrangeButtons.RightSize => $"{Glyphs.SizeHorizontal}",
-                ArrangeButtons.TopSize or ArrangeButtons.BottomSize => $"{Glyphs.SizeVertical}",
-                _ => base.Text
-            };
-        set => base.Text = value;
-    }
+    private string GetButtonGlyph () =>
+        ButtonType switch
+        {
+            ArrangeButtons.Move => $"{Glyphs.Move}",
+            ArrangeButtons.AllSize => $"{Glyphs.SizeBottomRight}",
+            ArrangeButtons.LeftSize or ArrangeButtons.RightSize => $"{Glyphs.SizeHorizontal}",
+            ArrangeButtons.TopSize or ArrangeButtons.BottomSize => $"{Glyphs.SizeVertical}",
+            _ => Text
+        };
 
     /// <summary>
     ///     Sets <see cref="Orientation"/> and <see cref="Direction"/> based on <see cref="ButtonType"/>.

Terminal.Gui/ViewBase/Adornment/TitleView.cs

@@ -112,7 +112,12 @@ protected override bool OnGettingAttributeForRole (in VisualRole role, ref Attri
     public NavigationDirection Direction { get; set; }
 
     /// <inheritdoc/>
-    public override string Text { get => base.Text; set => base.Text = Title = value; }
+    protected override void OnTextChanged ()
+    {
+        Title = Text;
+
+        base.OnTextChanged ();
+    }
 
     /// <summary>
     ///     Binds the appropriate arrow keys to their directional <see cref="Command"/> based on

Terminal.Gui/ViewBase/View.Text.cs

@@ -1,14 +1,11 @@
+using System.ComponentModel;
+
 namespace Terminal.Gui.ViewBase;
 
 public partial class View // Text Property APIs
 {
     private string _text = string.Empty;
 
-    /// <summary>
-    ///     Called when the <see cref="Text"/> has changed. Fires the <see cref="TextChanged"/> event.
-    /// </summary>
-    public void OnTextChanged () => TextChanged?.Invoke (this, EventArgs.Empty);
-
     /// <summary>
     ///     Gets or sets whether trailing spaces at the end of word-wrapped lines are preserved
     ///     or not when <see cref="Text.TextFormatter.WordWrap"/> is enabled.
@@ -50,9 +47,19 @@ public bool PreserveTrailingSpaces
     ///         If <see cref="View.Width"/> or <see cref="View.Height"/> are using <see cref="DimAutoStyle.Text"/>,
     ///         the <see cref="GetContentSize ()"/> will be adjusted to fit the text.
     ///     </para>
-    ///     <para>When the text changes, the <see cref="TextChanged"/> is fired.</para>
+    ///     <para>
+    ///         Setting <see cref="Text"/> to the same value as the current value is a no-op; neither
+    ///         <see cref="TextChanging"/> nor <see cref="TextChanged"/> will be raised.
+    ///     </para>
+    ///     <para>
+    ///         Before the text is changed, the <see cref="TextChanging"/> CWP hook is invoked. If cancelled,
+    ///         the text remains unchanged and <see cref="TextChanged"/> is not raised.
+    ///     </para>
+    ///     <para>
+    ///         After the text is changed, the <see cref="TextChanged"/> event is raised.
+    ///     </para>
     /// </remarks>
-    public virtual string Text
+    public string Text
     {
         get => _text;
         set
@@ -62,14 +69,107 @@ public virtual string Text
                 return;
             }
 
-            _text = value;
+            if (OnTextChanging (value))
+            {
+                return;
+            }
 
-            UpdateTextFormatterText ();
-            SetNeedsLayout ();
-            OnTextChanged ();
+            SetTextDirect (value);
+
+            RaiseTextChanged ();
         }
     }
 
+    /// <summary>
+    ///     Sets the <see cref="Text"/> backing field directly without raising <see cref="TextChanging"/>
+    ///     or <see cref="TextChanged"/> events and without invoking the <see cref="OnTextChanging"/>
+    ///     or <see cref="OnTextChanged"/> virtual methods.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         Use this method in derived views that maintain an internal text model (e.g., an editor
+    ///         buffer) and need to keep <see cref="Text"/> in sync after internal edits without
+    ///         re-entering the CWP flow.
+    ///     </para>
+    /// </remarks>
+    /// <param name="value">The new text value to store.</param>
+    protected void SetTextDirect (string value)
+    {
+        _text = value;
+        UpdateTextFormatterText ();
+        SetNeedsLayout ();
+    }
+
+    /// <summary>
+    ///     Called before the <see cref="Text"/> changes. Invokes the <see cref="TextChanging"/> event, which can
+    ///     be cancelled.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         The base implementation raises the <see cref="TextChanging"/> event. Override in derived views
+    ///         to perform validation or fire control-specific pre-change events.
+    ///     </para>
+    /// </remarks>
+    /// <param name="newText">The proposed new text value.</param>
+    /// <returns><see langword="true"/> if the text change should be cancelled; otherwise <see langword="false"/>.</returns>
+    protected virtual bool OnTextChanging (string newText)
+    {
+        CancelEventArgs args = new ();
+        TextChanging?.Invoke (this, args);
+
+        return args.Cancel;
+    }
+
+    /// <summary>
+    ///     Raised when the <see cref="Text"/> is about to change. Set <see cref="CancelEventArgs.Cancel"/> to
+    ///     <see langword="true"/> to prevent the change.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         This is a signal-only notification at the <see cref="View"/> level. It does not carry old or new
+    ///         text values. Derived controls that need richer text-edit semantics may expose their own specific events.
+    ///     </para>
+    /// </remarks>
+    public event EventHandler<CancelEventArgs>? TextChanging;
+
+    /// <summary>
+    ///     Called after the <see cref="Text"/> has been changed.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         Override in derived views to react to text changes. The base implementation is empty.
+    ///         The <see cref="TextChanged"/> event is raised by the caller after this method returns.
+    ///     </para>
+    /// </remarks>
+    protected virtual void OnTextChanged () { }
+
+    /// <summary>
+    ///     Invokes the CWP post-change workflow for <see cref="Text"/>: calls <see cref="OnTextChanged"/>
+    ///     then raises <see cref="TextChanged"/>.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         Derived views that bypass the base <see cref="Text"/> setter (e.g., using <c>new</c>) should
+    ///         call this method after mutating text to participate in the CWP workflow.
+    ///     </para>
+    /// </remarks>
+    protected internal void RaiseTextChanged ()
+    {
+        OnTextChanged ();
+        TextChanged?.Invoke (this, EventArgs.Empty);
+    }
+
+    /// <summary>
+    ///     Raised after the <see cref="Text"/> has been changed.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         This is a signal-only notification at the <see cref="View"/> level. It does not carry old or new
+    ///         text values. Derived controls that need richer text-edit semantics may expose their own specific events.
+    ///     </para>
+    /// </remarks>
+    public event EventHandler? TextChanged;
+
     /// <summary>
     ///     Gets or sets how the View's <see cref="Text"/> is aligned horizontally when drawn. Changing this property will
     ///     redisplay the <see cref="View"/>.
@@ -92,11 +192,6 @@ public Alignment TextAlignment
         }
     }
 
-    /// <summary>
-    ///     Text changed event, raised when the text has changed.
-    /// </summary>
-    public event EventHandler? TextChanged;
-
     /// <summary>
     ///     Gets or sets the direction of the View's <see cref="Text"/>. Changing this property will redisplay the
     ///     <see cref="View"/>.

Terminal.Gui/Views/Button.cs

@@ -170,13 +170,18 @@ private void SetMouseBindings (MouseFlags? mouseHoldRepeat)
 
     private void Button_TitleChanged (object? sender, EventArgs<string> e)
     {
-        base.Text = e.Value;
+        SetTextDirect (e.Value);
         TextFormatter.HotKeySpecifier = HotKeySpecifier;
         _interiorTextFormatter.HotKeySpecifier = HotKeySpecifier;
     }
 
     /// <inheritdoc/>
-    public override string Text { get => Title; set => base.Text = Title = value; }
+    protected override void OnTextChanged ()
+    {
+        Title = Text;
+
+        base.OnTextChanged ();
+    }
 
     /// <inheritdoc/>
     public override Rune HotKeySpecifier

Terminal.Gui/Views/CheckBox.cs

@@ -63,12 +63,17 @@ protected override void OnActivated (ICommandContext? commandContext)
 
     private void Checkbox_TitleChanged (object? sender, EventArgs<string> e)
     {
-        base.Text = e.Value;
+        SetTextDirect (e.Value);
         TextFormatter.HotKeySpecifier = HotKeySpecifier;
     }
 
     /// <inheritdoc/>
-    public override string Text { get => Title; set => base.Text = Title = value; }
+    protected override void OnTextChanged ()
+    {
+        Title = Text;
+
+        base.OnTextChanged ();
+    }
 
     /// <inheritdoc/>
     public override Rune HotKeySpecifier { get => base.HotKeySpecifier; set => TextFormatter.HotKeySpecifier = base.HotKeySpecifier = value; }

Terminal.Gui/Views/Code.cs

@@ -13,19 +13,11 @@ public Code ()
     }
 
     /// <summary>Gets or sets the source text to render.</summary>
-    public override string Text
+    protected override void OnTextChanged ()
     {
-        get => base.Text;
-        set
-        {
-            if (base.Text == value)
-            {
-                return;
-            }
+        UpdateStyledLines ();
 
-            base.Text = value;
-            UpdateStyledLines ();
-        }
+        base.OnTextChanged ();
     }
 
     /// <summary>Gets or sets the language hint used for syntax highlighting.</summary>

Terminal.Gui/Views/Color/ColorPicker.cs

@@ -153,16 +153,26 @@ protected override bool OnDrawingContent (DrawContext? context)
     protected virtual void OnValueChanged (ValueChangedEventArgs<Color?> args) { }
 
     /// <inheritdoc/>
-    public override string Text
+    protected override bool OnTextChanging (string newText)
     {
-        get => SelectedColor.ToString ();
-        set
+        // Reject text that cannot be parsed as a valid color
+        if (!_colorNameResolver.TryParseColor (newText, out _))
         {
-            if (_colorNameResolver.TryParseColor (value, out Color newColor))
-            {
-                SelectedColor = newColor;
-            }
+            return true;
+        }
+
+        return base.OnTextChanging (newText);
+    }
+
+    /// <inheritdoc/>
+    protected override void OnTextChanged ()
+    {
+        if (_colorNameResolver.TryParseColor (Text, out Color newColor))
+        {
+            SelectedColor = newColor;
         }
+
+        base.OnTextChanged ();
     }
 
     /// <summary>
@@ -288,6 +298,9 @@ private void SetSelectedColor (Color value, bool syncBars)
             // Do the work
             _selectedColor = value;
 
+            // Keep Text in sync with the new color
+            SetTextDirect (_selectedColor.ToString ());
+
             // CWP: Fire ValueChanged
             ValueChangedEventArgs<Color?> changedArgs = new (oldValue, value);
             OnValueChanged (changedArgs);

Terminal.Gui/Views/DatePicker.cs

@@ -47,16 +47,26 @@ public CultureInfo? Culture
     }
 
     /// <inheritdoc/>
-    public override string Text
+    protected override bool OnTextChanging (string newText)
     {
-        get => Value.ToString (Format);
-        set
+        // Reject text that cannot be parsed as a valid DateTime
+        if (!DateTime.TryParse (newText, out _))
         {
-            if (DateTime.TryParse (value, out DateTime result))
-            {
-                Value = result;
-            }
+            return true;
+        }
+
+        return base.OnTextChanging (newText);
+    }
+
+    /// <inheritdoc/>
+    protected override void OnTextChanged ()
+    {
+        if (DateTime.TryParse (Text, out DateTime result))
+        {
+            Value = result;
         }
+
+        base.OnTextChanged ();
     }
 
     #region IValue<DateTime> Implementation
@@ -90,6 +100,9 @@ public DateTime Value
 
             _date = value;
 
+            // Keep Text in sync with the new date value
+            SetTextDirect (_date.ToString (Format));
+
             // Propagate value to embedded editor
             _dateEditor?.Value = value;