Don't modify text due to binding when typing.

If a TextBox is e.g. bound to an int and the user types "02" then the
TextBox text should be "02" - not the value that comes back from the
binding which will be "2".

src/Avalonia.Controls/TextBox.cs

@@ -90,6 +90,7 @@ namespace Avalonia.Controls
         private bool _canScrollHorizontally;
         private TextPresenter _presenter;
         private UndoRedoHelper<UndoRedoState> _undoRedoHelper;
+        private bool _ignoreTextChanges;
 
         static TextBox()
         {
@@ -184,7 +185,13 @@ namespace Avalonia.Controls
         public string Text
         {
             get { return _text; }
-            set { SetAndRaise(TextProperty, ref _text, value); }
+            set
+            {
+                if (!_ignoreTextChanges)
+                {
+                    SetAndRaise(TextProperty, ref _text, value);
+                }
+            }
         }
 
         public TextAlignment TextAlignment
@@ -247,7 +254,7 @@ namespace Avalonia.Controls
                     DeleteSelection();
                     caretIndex = CaretIndex;
                     text = Text ?? string.Empty;
-                    Text = text.Substring(0, caretIndex) + input + text.Substring(caretIndex);
+                    SetTextInternal(text.Substring(0, caretIndex) + input + text.Substring(caretIndex));
                     CaretIndex += input.Length;
                     SelectionStart = SelectionEnd = CaretIndex;
                     _undoRedoHelper.DiscardRedo();
@@ -355,7 +362,7 @@ namespace Avalonia.Controls
                 case Key.Back:
                     if (!DeleteSelection() && CaretIndex > 0)
                     {
-                        Text = text.Substring(0, caretIndex - 1) + text.Substring(caretIndex);
+                        SetTextInternal(text.Substring(0, caretIndex - 1) + text.Substring(caretIndex));
                         --CaretIndex;
                     }
 
@@ -364,7 +371,7 @@ namespace Avalonia.Controls
                 case Key.Delete:
                     if (!DeleteSelection() && caretIndex < text.Length)
                     {
-                        Text = text.Substring(0, caretIndex) + text.Substring(caretIndex + 1);
+                        SetTextInternal(text.Substring(0, caretIndex) + text.Substring(caretIndex + 1));
                     }
 
                     break;
@@ -598,7 +605,7 @@ namespace Avalonia.Controls
                     var start = Math.Min(selectionStart, selectionEnd);
                     var end = Math.Max(selectionStart, selectionEnd);
                     var text = Text;
-                    Text = text.Substring(0, start) + text.Substring(end);
+                    SetTextInternal(text.Substring(0, start) + text.Substring(end));
                     SelectionStart = SelectionEnd = CaretIndex = start;
                     return true;
                 }
@@ -645,6 +652,19 @@ namespace Avalonia.Controls
             return i;
         }
 
+        private void SetTextInternal(string value)
+        {
+            try
+            {
+                _ignoreTextChanges = true;
+                SetAndRaise(TextProperty, ref _text, value);
+            }
+            finally
+            {
+                _ignoreTextChanges = false;
+            }
+        }
+
         UndoRedoState UndoRedoHelper<UndoRedoState>.IUndoRedoHost.UndoRedoState
         {
             get { return new UndoRedoState(Text, CaretIndex); }

tests/Avalonia.Controls.UnitTests/TextBoxTests.cs

@@ -1,7 +1,14 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Avalonia.Controls.Presenters;
+using Avalonia.Controls.Templates;
 using Avalonia.Data;
+using Avalonia.Input;
+using Avalonia.Markup.Xaml.Data;
+using Avalonia.Platform;
+using Avalonia.UnitTests;
+using Moq;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests
@@ -15,5 +22,63 @@ namespace Avalonia.Controls.UnitTests
                 BindingMode.TwoWay,
                 TextBox.TextProperty.GetMetadata(typeof(TextBox)).DefaultBindingMode);
         }
+
+        [Fact]
+        public void Typing_Beginning_With_0_Should_Not_Modify_Text_When_Bound_To_Int()
+        {
+            using (UnitTestApplication.Start(Services))
+            {
+                var source = new Class1();
+                var target = new TextBox
+                {
+                    DataContext = source,
+                    Template = CreateTemplate(),
+                };
+
+                target.ApplyTemplate();
+                target.Bind(TextBox.TextProperty, new Binding(nameof(Class1.Foo), BindingMode.TwoWay));
+
+                Assert.Equal("0", target.Text);
+
+                target.CaretIndex = 1;
+                target.RaiseEvent(new TextInputEventArgs
+                {
+                    RoutedEvent = InputElement.TextInputEvent,
+                    Text = "2",
+                });
+
+                Assert.Equal("02", target.Text);
+            }
+        }
+
+        private static TestServices Services => TestServices.MockThreadingInterface.With(
+            standardCursorFactory: Mock.Of<IStandardCursorFactory>());
+
+        private IControlTemplate CreateTemplate()
+        {
+            return new FuncControlTemplate<TextBox>(control =>
+                new TextPresenter
+                {
+                    Name = "PART_TextPresenter",
+                    [!!TextPresenter.TextProperty] = new Binding
+                    {
+                        Path = "Text",
+                        Mode = BindingMode.TwoWay,
+                        Priority = BindingPriority.TemplatedParent,
+                        RelativeSource = new RelativeSource(RelativeSourceMode.TemplatedParent),
+                    },
+                });
+        }
+
+        private class Class1 : NotifyingBase
+        {
+            private int _foo;
+
+            public int Foo
+            {
+                get { return _foo; }
+                set { _foo = value; RaisePropertyChanged(); }
+            }
+        }
     }
 }