Wpf: Fix TextBox.Text so it clears the undo buffer when set

src/Eto.Wpf/Forms/Controls/TextBoxHandler.cs

@@ -298,55 +298,53 @@ public string Text
 				var oldText = Text;
 				CurrentText = null;
 				var newText = value ?? string.Empty;
-				TextBox.BeginChange();
-				if (newText != oldText)
-				{
-					var args = new TextChangingEventArgs(oldText, newText, false);
-					Callback.OnTextChanging(Widget, args);
-					if (args.Cancel)
-					{
-						TextBox.EndChange();
-						return;
-					}
+				if (newText == oldText)
+					return;
 
-					var needsTextChanged = TextBox.Text == newText;
+				var args = new TextChangingEventArgs(oldText, newText, false);
+				Callback.OnTextChanging(Widget, args);
+				if (args.Cancel)
+					return;
 
-					// Improve performance when setting text often
-					// See https://github.com/dotnet/wpf/issues/5887#issuecomment-1604577981
-					var endNoGCRegion = EnableNoGCRegion
-						&& GCSettings.LatencyMode != GCLatencyMode.NoGCRegion;
+				var needsTextChanged = TextBox.Text == newText;
 
-					try
-					{
-						endNoGCRegion &= GC.TryStartNoGCRegion(1000000); // is this magic number reasonable??
-					}
-					catch
-					{
-						// Ignore any exceptions, they can apparently still happen even though we check the LatencyMode above
-						endNoGCRegion = false;
-					}
+				// Improve performance when setting text often
+				// See https://github.com/dotnet/wpf/issues/5887#issuecomment-1604577981
+				var endNoGCRegion = EnableNoGCRegion
+					&& GCSettings.LatencyMode != GCLatencyMode.NoGCRegion;
 
-					try 
-					{
-						TextBox.Text = newText; 
-					}
-					finally
-					{
-						if (endNoGCRegion && GCSettings.LatencyMode == GCLatencyMode.NoGCRegion)
-							GC.EndNoGCRegion();
-					}
-
-					if (needsTextChanged)
-					{
-						Callback.OnTextChanged(Widget, EventArgs.Empty);
-					}
+				try
+				{
+					endNoGCRegion &= GC.TryStartNoGCRegion(1000000); // is this magic number reasonable??
 				}
+				catch
+				{
+					// Ignore any exceptions, they can apparently still happen even though we check the LatencyMode above
+					endNoGCRegion = false;
+				}
+
+				try 
+				{
+					TextBox.Text = newText; 
+				}
+				finally
+				{
+					if (endNoGCRegion && GCSettings.LatencyMode == GCLatencyMode.NoGCRegion)
+						GC.EndNoGCRegion();
+				}
+
 				if (value != null && AutoSelectMode == AutoSelectMode.Never && !HasFocus)
 				{
+					TextBox.BeginChange();
 					TextBox.SelectionStart = value.Length;
 					TextBox.SelectionLength = 0;
+					TextBox.EndChange();
+				}
+
+				if (needsTextChanged)
+				{
+					Callback.OnTextChanged(Widget, EventArgs.Empty);
 				}
-				TextBox.EndChange();
 			}
 		}
 

test/Eto.Test/UnitTests/Forms/Controls/TextBoxTests.cs

@@ -6,6 +6,34 @@ namespace Eto.Test.UnitTests.Forms.Controls
 	public abstract class TextBoxBase<T> : TestBase
 		where T: TextBox, new()
 	{
+		[Test, ManualTest]
+		public void SettingTextShouldClearUndoBuffer()
+		{
+			ManualForm("Try typing and undo/redo, then press the button to reset. After reset, it should not undo to previous values", form =>
+			{
+				var textBox = new T();
+				textBox.Text = "Hello";
+				textBox.SelectAll();
+
+				var button = new Button { Text = "Click Me" };
+				button.Click += (sender, e) =>
+				{
+					textBox.Text = "Thanks, now try to undo";
+					textBox.Focus();
+				};
+
+				return new TableLayout
+				{
+					Spacing = new Size(5, 5),
+					Padding = 10,
+					Rows = {
+						textBox,
+						button
+					}
+				};
+			});
+		}
+
 		[Test, ManualTest]
 		public void CaretIndexShouldStartInInitialPosition()
 		{