From d22282c15155b74f04fb2f70351191104e3c7e3a Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Wed, 1 May 2019 14:53:14 +0200
Subject: [PATCH 1/2] Added failing tests for #2470.

---
 .../Data/BindingTests.cs                      | 22 ++++++++++++++
 .../Xaml/BindingTests.cs                      | 29 ++++++++++++++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs b/tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs
index baa1bca76a..d19accb0ad 100644
--- a/tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs
+++ b/tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs
@@ -100,6 +100,28 @@ namespace Avalonia.Markup.UnitTests.Data
             Assert.Equal("baz", target.Text);
         }
 
+        [Fact]
+        public void OneWayToSource_Binding_Should_React_To_DataContext_Changed()
+        {
+            var target = new TextBlock { Text = "bar" };
+            var binding = new Binding
+            {
+                Path = "Foo",
+                Mode = BindingMode.OneWayToSource,
+            };
+
+            target.Bind(TextBox.TextProperty, binding);
+
+            var source = new Source { Foo = "foo" };
+            target.DataContext = source;
+
+            Assert.Equal("bar", source.Foo);
+            target.Text = "baz";
+            Assert.Equal("baz", source.Foo);
+            source.Foo = "quz";
+            Assert.Equal("baz", target.Text);
+        }
+
         [Fact]
         public void Default_BindingMode_Should_Be_Used()
         {
diff --git a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BindingTests.cs b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BindingTests.cs
index fef9dfb675..14abebcdb5 100644
--- a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BindingTests.cs
+++ b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BindingTests.cs
@@ -329,6 +329,33 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 
                 Assert.Equal("Hello world", textBlock.Text); 
             }
-        } 
+        }
+
+        [Fact]
+        public void Binding_OneWayToSource_Works()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        ShowInTaskbar='{Binding ShowInTaskbar, Mode=OneWayToSource}'>
+</Window>";
+                var loader = new AvaloniaXamlLoader();
+                var window = (Window)loader.Load(xaml);
+                var viewModel = new WindowViewModel();
+
+                window.DataContext = viewModel;
+                window.ApplyTemplate();
+
+                Assert.True(window.ShowInTaskbar);
+                Assert.True(viewModel.ShowInTaskbar);
+            }
+        }
+
+        private class WindowViewModel
+        {
+            public bool ShowInTaskbar { get; set; }
+        }
     }
 }

From 197d7d4904b4767d882c676232cad67ffe3fd566 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Wed, 1 May 2019 14:54:20 +0200
Subject: [PATCH 2/2] Update OneWayToSource binding when DataContext changes.

Fixes #2470
---
 src/Avalonia.Base/Data/BindingOperations.cs         | 6 +++++-
 src/Avalonia.Base/Data/Core/PropertyAccessorNode.cs | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Base/Data/BindingOperations.cs b/src/Avalonia.Base/Data/BindingOperations.cs
index ca148659e6..15de6c4d0d 100644
--- a/src/Avalonia.Base/Data/BindingOperations.cs
+++ b/src/Avalonia.Base/Data/BindingOperations.cs
@@ -65,7 +65,11 @@ namespace Avalonia.Data
                         return Disposable.Empty;
                     }
                 case BindingMode.OneWayToSource:
-                    return target.GetObservable(property).Subscribe(binding.Subject);
+                    return Observable.CombineLatest(
+                        binding.Observable,
+                        target.GetObservable(property),
+                        (_, v) => v)
+                    .Subscribe(x => binding.Subject.OnNext(x));
                 default:
                     throw new ArgumentException("Invalid binding mode.");
             }
diff --git a/src/Avalonia.Base/Data/Core/PropertyAccessorNode.cs b/src/Avalonia.Base/Data/Core/PropertyAccessorNode.cs
index a916142675..df8f46a7d7 100644
--- a/src/Avalonia.Base/Data/Core/PropertyAccessorNode.cs
+++ b/src/Avalonia.Base/Data/Core/PropertyAccessorNode.cs
@@ -59,8 +59,8 @@ namespace Avalonia.Data.Core
                     $"Could not find a matching property accessor for {PropertyName}.");
             }
 
-            accessor.Subscribe(ValueChanged);
             _accessor = accessor;
+            accessor.Subscribe(ValueChanged);
         }
 
         protected override void StopListeningCore()