TextBox programmatic Undo/Redo & CanUndo/CanRedo

src/Avalonia.Controls/TextBox.cs

@@ -17,7 +17,6 @@ using Avalonia.Controls.Metadata;
 using Avalonia.Media.TextFormatting;
 using Avalonia.Media.TextFormatting.Unicode;
 using Avalonia.Automation.Peers;
-using System.Diagnostics;
 using Avalonia.Threading;
 
 namespace Avalonia.Controls
@@ -166,6 +165,18 @@ namespace Avalonia.Controls
                 (o, v) => o.UndoLimit = v,
                 unsetValue: -1);
 
+        /// <summary>
+        /// Defines the <see cref="CanUndo"/> property
+        /// </summary>
+        public static readonly DirectProperty<TextBox, bool> CanUndoProperty =
+            AvaloniaProperty.RegisterDirect<TextBox, bool>(nameof(CanUndo), x => x.CanUndo);
+
+        /// <summary>
+        /// Defines the <see cref="CanRedo"/> property
+        /// </summary>
+        public static readonly DirectProperty<TextBox, bool> CanRedoProperty =
+            AvaloniaProperty.RegisterDirect<TextBox, bool>(nameof(CanRedo), x => x.CanRedo);
+
         /// <summary>
         /// Defines the <see cref="CopyingToClipboard"/> event.
         /// </summary>
@@ -232,6 +243,8 @@ namespace Avalonia.Controls
         private bool _canPaste;
         private string _newLine = Environment.NewLine;
         private static readonly string[] invalidCharacters = new String[1] { "\u007f" };
+        private bool _canUndo;
+        private bool _canRedo;
 
         private int _wordSelectionStart = -1;
         private int _selectedTextChangesMadeSinceLastUndoSnapshot;
@@ -590,6 +603,24 @@ namespace Avalonia.Controls
             }
         }
 
+        /// <summary>
+        /// Gets a value that indicates whether the undo stack has an action that can be undone
+        /// </summary>
+        public bool CanUndo
+        {
+            get => _canUndo;
+            private set => SetAndRaise(CanUndoProperty, ref _canUndo, value);
+        }
+
+        /// <summary>
+        /// Gets a value that indicates whether the redo stack has an action that can be redone
+        /// </summary>
+        public bool CanRedo
+        {
+            get => _canRedo;
+            private set => SetAndRaise(CanRedoProperty, ref _canRedo, value);
+        }
+
         public event EventHandler<RoutedEventArgs>? CopyingToClipboard
         {
             add => AddHandler(CopyingToClipboardEvent, value);
@@ -943,30 +974,13 @@ namespace Avalonia.Controls
             }
             else if (Match(keymap.Undo) && IsUndoEnabled)
             {
-                try
-                {
-                    SnapshotUndoRedo();
-                    _isUndoingRedoing = true;
-                    _undoRedoHelper.Undo();
-                }
-                finally
-                {
-                    _isUndoingRedoing = false;
-                }
+                Undo();
 
                 handled = true;
             }
             else if (Match(keymap.Redo) && IsUndoEnabled)
             {
-                try
-                {
-                    _isUndoingRedoing = true;
-                    _undoRedoHelper.Redo();
-                }
-                finally
-                {
-                    _isUndoingRedoing = false;
-                }
+                Redo();
 
                 handled = true;
             }
@@ -1703,5 +1717,60 @@ namespace Avalonia.Controls
                 }
             }
         }
+
+        /// <summary>
+        /// Undoes the first action in the undo stack
+        /// </summary>
+        public void Undo()
+        {
+            if (IsUndoEnabled && CanUndo)
+            {
+                try
+                {
+                    SnapshotUndoRedo();
+                    _isUndoingRedoing = true;
+                    _undoRedoHelper.Undo();
+                }
+                finally
+                {
+                    _isUndoingRedoing = false;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Reapplies the first item on the redo stack
+        /// </summary>
+        public void Redo()
+        {
+            if (IsUndoEnabled && CanRedo)
+            {
+                try
+                {
+                    _isUndoingRedoing = true;
+                    _undoRedoHelper.Redo();
+                }
+                finally
+                {
+                    _isUndoingRedoing = false;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Called from the UndoRedoHelper when the undo stack is modified
+        /// </summary>
+        void UndoRedoHelper<UndoRedoState>.IUndoRedoHost.OnUndoStackChanged()
+        {
+            CanUndo = _undoRedoHelper.CanUndo;
+        }
+
+        /// <summary>
+        /// Called from the UndoRedoHelper when the redo stack is modified
+        /// </summary>
+        void UndoRedoHelper<UndoRedoState>.IUndoRedoHost.OnRedoStackChanged()
+        {
+            CanRedo = _undoRedoHelper.CanRedo;
+        }           
     }
 }

src/Avalonia.Controls/Utils/UndoRedoHelper.cs

@@ -14,6 +14,10 @@ namespace Avalonia.Controls.Utils
         public interface IUndoRedoHost
         {
             TState UndoRedoState { get; set; }
+
+            void OnUndoStackChanged();
+
+            void OnRedoStackChanged();
         }
 
 
@@ -28,6 +32,10 @@ namespace Avalonia.Controls.Utils
         /// </summary>
         public int Limit { get; set; } = 10;
 
+        public bool CanUndo => _currentNode?.Previous != null;
+
+        public bool CanRedo => _currentNode?.Next != null;
+
         public UndoRedoHelper(IUndoRedoHost host)
         {
             _host = host;
@@ -39,6 +47,8 @@ namespace Avalonia.Controls.Utils
             {
                 _currentNode = _currentNode.Previous;
                 _host.UndoRedoState = _currentNode.Value;
+                _host.OnUndoStackChanged();
+                _host.OnRedoStackChanged();
             }
         }
 
@@ -72,6 +82,8 @@ namespace Avalonia.Controls.Utils
         {
             while (_currentNode?.Next != null)
                 _states.Remove(_currentNode.Next);
+
+            _host.OnRedoStackChanged();
         }
 
         public void Redo()
@@ -80,6 +92,8 @@ namespace Avalonia.Controls.Utils
             {
                 _currentNode = _currentNode.Next;
                 _host.UndoRedoState = _currentNode.Value;
+                _host.OnRedoStackChanged();
+                _host.OnUndoStackChanged();
             }
         }
 
@@ -94,6 +108,9 @@ namespace Avalonia.Controls.Utils
                 _currentNode = _states.Last;
                 if (Limit != -1 && _states.Count > Limit)
                     _states.RemoveFirst();
+
+                _host.OnUndoStackChanged();
+                _host.OnRedoStackChanged();
             }
         }
 
@@ -101,6 +118,9 @@ namespace Avalonia.Controls.Utils
         {
             _states.Clear();
             _currentNode = null;
+
+            _host.OnUndoStackChanged();
+            _host.OnRedoStackChanged();
         }
     }
 }